Aesculapian Snakes in London

Page originally created in July 2011 and last updated: 25th October 2024

Inner-city Serpent  -  3.5ft adult female Aesculapian Snake at Regent's Canal, London, 2016

Aesculapian Snake  (Zamenis longissimus, previously Elaphe longissima & Coluber longissimus)

Here in the UK we have three native snake species and two introduced species of snake that have established breeding colonies at specific sites. The five snake species found are:

Native:    Adder / Northern Viper (Vipera berus),     Barred Grass Snake (Natrix helvetica),     Smooth Snake (Coronella austriaca)  

Introduced:    Aesculapian Snake (Zamenis longissimus),    Eastern Romanian Grass Snake (Natrix natrix persa)

The fourth snake is the introduced Aesculapian Rat Snake. Aesculapian Snakes are originally from mainland Europe, but small colonies are currently established in two specific parts of the UK. Aesculapian Snakes haven't been resident in the UK for at least 20,000 years, and probably more than 120,000 years, and they are now considered by Natural England to be non-native to the UK. However, there are two well established breeding colonies of Aesculapian Snakes here in Great Britain that have been in existence now for over 35 years. The oldest introduced colony of Aesculapian Snakes in the UK, is in Colwyn Bay, North Wales. The second colony is in Camden, Central London, in England. Outside of the UK the nearest populations of wild and native Aesculapian Snakes are found in northern France.

These long slender Rat Snakes, of the Colubridae family, are Old World Snakes and are one of Europe's longest snakes. They regularly grow to a length of 140-160cm. In warmer parts of Europe they can reach up to 180cm and have even reached 225cm on one occasion. This easily makes them the longest snake found in the UK, and one of the longest in Europe. The maximum weight for males is usually around 890 grams and 550 grams for females. These snakes are usually found across southern, central and eastern Europe and prefer the same method of incubating their eggs as our native Grass Snakes, using warm damp moist areas of rotting vegetation, such as hay piles and compost heaps, to provide the necessary heat. Aesculapian Snakes are the only semi-arboreal snake in Europe. Not only are they are excellent climbers but are equally at home high up in trees and bushes as they are on the ground. They can on occasion be found basking on the canopies of trees and tall bushes, or on roof-tops of buildings in their native range. In Europe they are regularly encountered on the edges of Beech and Oak forests at lower altitudes, as well as open grass fields and meadows surrounded by bushes, and dry stone walls. They can also be found in shrubs that border lakes and river banks.

Male Aesculapian Snake at Regents Canal, London. 2020

So where did they come from and how did the two separate populations of Aesculapian Snakes end up here in the UK? 

1) Colwyn Bay population of Aesculapian Snakes in North Wales.

In 2006 the Welsh colony of Aesculapian Snakes was estimated at around 85 adult and 365 juvenile specimens, and originally came about during the early 1960's after a gravid female snake, affectionately referred to as "Old Essie" by the 2003 assistant curator Peter Dickinson, escaped from the Welsh Mountain Zoo at Colwyn Bay and laid her eggs within the grounds of the zoo. The offspring then successfully bred and the population has thrived ever since in and around the zoo grounds. The first feral snake born within the grounds of the Welsh Mountain Zoo was found crossing a pathway within the grounds of the zoo in 1963, and was quickly identified as an Aesculapian Snake. It is quite possible that this colony derived from more than just one escaped specimen though. According to the NNSS website the first official record of these snakes living wild in Colwyn Bay was in 1970. They were first reported by the press during the early '70's. Software analysis has however suggested that several individual specimens probably comprised the founder stock rather than just one specimen according to the 2009 book "The Naturalised Animals Of Britain & Ireland" by Christopher Lever. Since its introduction this colony has not spread far from the zoo in its 60 years of existence, confirming that this species probably has a low dispersal ability, and is reliant on woodland connectivity to travel. It is also very likely that due to the abundance of rodent prey surrounding the Colwyn Bay Zoo that these snakes are reluctant to leave this food-rich location. The main egg laying site for this snake population had long been suspected to be the manure dump at the Zoo. Ongoing studies revealed in 2021 that these snakes are using both the zoo's manure dump and offsite compost heaps as egg-laying sites.

The Welsh Mountain Zoo at Colwyn Bay was founded in 1963 by Robert Jackson. Robert Jackson was an importer and dealer of reptiles, amphibians, mammals and birds. One of the many species he sold in the 1950's & 60's was the Aesculapian Snake. See link here

The Colwyn Bay colony of Aesculapian Snakes is now the most northerly colony of this species currently found in existence anywhere in the world. Historically though the Aesculapian Snake's range once extended as far north as NW Denmark, which is even further north than Edinburgh would be in the UK.

2) London colony of Aesculapian Snakes.

I have personally been studying and photographing the Aesculapian Snakes in London for thirteen years now, since 2011. My sightings and observations have continually been added to the database held by Will Atkins, as have records that I have forwarded to Will from other sightings by members of the public. By 2018 the London population of Aesculapian Snakes had seen 50 different adult specimens recorded and photographed, and in 2013 this population was then estimated at around 40 specimens. However the number of these urbanised snakes seems to have fallen significantly in London over recent years. Between 2016 -2021 the number of sightings has seen a definite decline and there are serious concerns as to how many of this once thriving population of feral snakes may still exist in 2023. This population is confined to a small area of around two hectares in Central London, surrounded by busy roads, and could only spread beyond this range by travelling great distances along Regents Canal itself, or by crossing these busy roads. During 2022 and 2023 the number of sightings did seem to be increasing, but this may just be because theses snakes are becoming less fearful of humans due to constant exposure to high levels of human traffic along the canal tow-path at Regents Canal. Public awareness of the species has increased significantly in recent years, due to coverage from the British media, and from sightings being shared on social media platforms such as Facebook and TikTok. This has led to a huge increase in the number of people actively looking for these snakes to photograph for themselves.

With the feral population of London Aesculapian Snakes being found in, and very close to, the grounds of London Zoo it would be easy for one to jump to conclusions. But despite the obvious theory that the London population of Aesculapian Snakes must have derived from one or more escapees from London Zoo, this surprisingly isn't the case.

So if these snakes didn't originate as escapees from London Zoo then how did they get there? It is widely accepted that this population came about after about eight individual specimens of Aesculapian Snake were deliberately released along the banks of Regent's Canal in the mid 1980's from the "Centre For Life Studies", a building located at Zoological Gardens, Regents Park, NW1, adjacent to London Zoo, and rented by ILEA (Inner London Education Authority facility for scientific experiments). Within the circles of respected herpetologists, some still claim to know exactly which former ILEA staff member was responsible for releasing these snakes onto the banks of Regent's Canal. However some former ILEA employees insisted that these snakes escaped and were not deliberately released.

After repeated sightings of an unknown snake species along the banks of Regents Canal during the 1990s theses snakes were finally identified from photographs, and in 1998 reported to TESL by Ester Wenman, who was at that time the head keeper of reptiles at London Zoo. This growing population of Aesculapians in London became common knowledge amongst many herpetologists in April 2007, via a popular online British herpetology forum, Reptiles & Amphibians UK, and many herpetologists travelled to London to find and photograph these snakes for themselves.

In an interview with the Camden Review in 2010 David Bird, a former zoo curator, also told the reporter that the Aesculapian Snakes either escaped from or were deliberately released from the ILEA building: Camden Review article

Christopher Lever discussed the London Aesculapians in his 2009 book "The Naturalised Animals Of Britain & Ireland" by Christopher Lever", and Will Atkins & Tom Langton then went into more detail about the origins of the London Aesculapian Snakes in 2011 when they wrote a detailed account in The London Naturalist No.90, 2011 on pages 93-95, giving this summary:

"A second feral population has been extant since the mid 1980s along a canal embankment habitat in Camden, north London. This was first reported to TESL in 1998 by Ester Wenman, then head keeper of reptiles at London Zoo. Aesculapian snakes had apparently colonised the area during an experiment reported by the British Herpetological Society Legal Officer, Peter Curry, who was working there and keeping this species at the Inner London Education Authority Centre for Life Studies at the time that it was closed down around 1986. One account was that eight snakes had been released ‘on the quiet’ around the time of closure to try to form a population, several of which were recaptured, but some remained at large. Those caught initially were being euthanized but the view was then taken to leave the others ‘to take their chances’ where they were. Ten years later, in an aviary close to the embankment, fragments of juvenile Aesculapian snakes were found in a laughing thrush Garrulax sp. aviary, suggesting that the snakes had bred."  The article also states, “Several newly born snakes were found in the basement of a building around 30 metres from the embankment in 2010, and breeding in that year was also shown in 2011 with a young 2010 cohort snake being located. To this date this is the only example of a non-native snake species breeding successfully and forming populations in the wild in London and the UK as a whole.”

A ZSL reptile keeper, who was working at London Zoo at the time when these snakes were released, claims these snakes were actually "deliberately released quite a while before the ILEA building was shut down". He claimed that during the 1990's the Aesculapian Snakes that were found by ZSL staff on the south bank of the canal would be captured and re-released back on the north bank of the canal, where the ILEA building was. One herpetologist ,that claims to have been close friends with the ILEA staff member who released the snakes at Regents Canal, has gone into more detail about the origins of the London Aesculapian Snakes. In 2022 he has publicly stated: "The person responsible for their release was a personal friend of mine for many years. The original specimens were collected from the wild in Italy (when it was still legal to do this). We do not know precisely how many snakes were released but with a little more research, we should be able to trace the locality they were originally collected from."

Natural England were slow to accept the existence of the London Aesculapian Snake colony. In their 22nd May 2009 report "Horizon scanning for new  invasive non-native animal  species in England", they discussed the Welsh colony of Aesculapian Snakes and went on to comment on the London colony saying " There are also anecdotal reports of individuals of this species in central London".  

The London Naturalist No.99, 2020, page 96 & 97

In November 2020 the 99th edition of The London Naturalist published a lengthy update on the London Aesculapian Snake colony, by Will Atkins, The article was compiled using data based on Will's own sightings of the Aesculapian Snakes at London, as well as records that were submitted by myself and others. Will was the first to study these snakes and his knowledge during the earlier years of the London Aesculapian Snakes is second to none. His well written and in-depth article mentioned many points that I have also written about on this website. Will's views and opinions often echoed that of my own when discussing the conservation status and fears for the future of these snakes in the UK. 

Jason Steel photographing an adult female Aesculapian Snake along Regents Canal in London, UK in 2016. Photo taken by Australian photographer Diane Paine.

Are Aesculapian Snakes an invasive species, and are they a threat to our native wildlife?

The simple answer to this question is no, not at all. For a species to be classed as invasive it firstly needs to be spreading, which neither of the UK colonies are. Secondly, it needs to be having a detrimental effect on our native species, which these snakes are not.

Following ongoing studies of these Aesculapian Snake populations in the UK by herpetologists including Wolfgang Wüster and Tom Major in Bangor, Wales, & Will Atkins and myself in London, it is clear that the existence of these snakes has had very little if any negative impact on our native wildlife. This is largely because in the UK they feed almost entirely on common rodents, which are found in abundance around both zoos. Whilst Zamenis longissimus are considered to be generalist predators their primary prey in London is the Brown Rat, Rattus norvegicus. The Brown Rat is a non-native species in the UK that was accidentally introduced to the British Isles around 1720, as a stowaway aboard sailing ships.  LINK

In 2016 one adult Aesculapian Snake specimen that was handled by a fellow amateur herpetologist, and friend of mine, quickly regurgitated six newly born rat pups. At this size the rat pups are far too young to leave their nest so this supports the knowledge that the Aesculapian Snakes are actively hunting rodents in their own burrows and hideaways. In 2021 another adult female Aesculapian Snake specimen, that was handled, regurgitated two young Brown Rats of 55mm & 60mm in body-length. Analysis of Aesculapian Snake droppings has also found traces of mouse hair. (The London Naturalist No.90, 2011, page 95). In 2021 studies of the Welsh colony of Aesculapian Snakes, by Tom Major & Bangor University, have revealed that these snakes have on occasion fed on ground nesting birds at that site too. Hatchling snakes there have fed on very young rodent pups. LINK  It's been reported in Croatia, where these snakes are native, that adult Aesculapian Snakes can feed as often as every three days in the warmer months. LINK  In their native range Aesculapian Snakes have also been known on occasion to feed on the eggs of ground nesting birds too. However, no such ground-nesting avian species exist in the vicinity of the London Aesculapian Snakes.

These snakes also seem dependent on woodland habitat connectivity in order to spread. In 60+ years since their arrival in the UK neither of these two populations of Aesculapian Snakes have been able to spread further than the sites where they are established. In London there simply aren't the necessary dispersal corridors available for the Aesculapian Snakes to disperse any further than they already have along the banks of the canal. And the population's distribution and reproduction is severely limited by the scarcity of suitable egg-laying sites.

It is largely down to the cooling climate over the past 5000 years that has seen a decrease in the distribution and numbers of Aesculapian Snakes across their native range in Continental Europe. With the undeniable current climate change that is already here and taking place across the world, temperatures in recent years are now once again on the increase. It is likely that the natural range of the Aesculapian Snakes found in Europe will change in the future. As temperatures continue to rise it is likely that many reptile species in Continental Europe, including the Aesculapian Snakes, will attempt to move further north and once again inhabit areas where they were previously found, if they are not prevented from doing so by busy roads that divide the land and isolate reptile populations in so many places. In Austria, where the Aesculapian Snake is considered both native and endangered, the Aesculapian Snake has already been recorded since 2014 as expanding its range both further north and higher in altitude. Where previously it was only found up to 1000m above sea-level it has now increased its range to 1200m above sea level. The same behaviour is also being seen with Adders in Austria too. See link here.

With Aesculapian Snakes already present in the NW of France it is only the English Channel that prevents any possibility of theses snakes from returning to British soil of their own accord in future years. It is known from fossil records that Aesculapian Snakes have previously lived alongside our British native species in the past and given the opportunity could do so once again, probably without issue if they could reach our southern shores. Aesculapian Snakes are found across much of Europe living side-by-side with many of the same species of wildlife that we have in the UK without any issues so it is still very unlikely that Aesculapian Snakes could ever become a threat to other native species.

Adult female Aesculapian Snake at Regents Canal, London. 2016

Are these snakes dangerous to humans?

No, not at all. The Aesculapian Snake is non-venomous and not an aggressive species. It also lacks the size or strength to inflict any harm to either humans or pet cats & dogs. Unless you're a rodent, a small bird or a young lizard, then you're quite safe from these snakes, despite what the press would have you believe.

Very occasionally Aesculapian Snakes have been known to put on a fake threat display by rapidly shaking their tail and beating it against the ground to imitate a Rattlesnake. This is not something that I have ever witnessed myself but this behaviour was filmed by Priroda Sjevera in Montenegro, in July 2024. - LINK

Adult female Aesculapian Snake by Regent's Canal, London. 2016

Adult female Aesculapian Snake, Regent's Canal, London, 2016

3ft sub-adult / young adult female Aesculapian Snake, found on the north bank of Regents Canal, 30th April 2023

These elegant snakes range in colour from light golden-brown to dark brown with white flecks and a creamy yellow underside. Aesculapian Snakes have unkeeled scales that are very smooth to the touch, and this snake can have a very shiny appearance with an iridescent sheen in bright sunlight. The overall appearance of the London Aesculapian Snakes is often compared to that of a Twix wrapper.

Adult female Aesculapian Snake, Regent's Canal, London, 2016

Ulike all the other snake species found in Britain, it is the male Aesculapian Snake that is usually longer than the female. The female tends to have greater girth but the male tends to be longer. The female pictured above had a total body-length of just 3.5ft. A male specimen with equivalent girth would probably have been 5ft+ in length.

Adult female Aesculapian Snake, Regent's Canal, London

This adult female specimen at London exhibits several scars along her body. These may have been caused by attempted predation by birds, foxes, domestic cats, or by defensive rodents and some snakes have suffered as a result of encounters with local council workers or groundsmen using strimmers to cut the grass. Groundsmen workers at ZSL bear witness to Magpies being seen attacking these snakes on several occasions.

Adult female Aesculapian Snake, Regent's Canal, London

Will Atkins spent many years photographing and recording individual specimens of the Aesculapian Snake population in London from the summer of 2007 right up until around 2019. His photographic database allows him to identify individual snake specimens by studying unique scale markings on the head of each snake. This close-up shot of the snake's head shows the smooth un-keeled scales of the adult female Aesculapian Snake, which was identified from Will Atkin's database as snake number 15 of the London population.

This individual snake has been recorded on both sides of the canal. Whether it uses the footbridges or whether it swims across the canal is uncertain as these snakes have been filmed by members of the public on and adjacent to the footbridges. In 2011 I spoke to the owner of a canal-boat moored along Regent's Canal in 2011 who told me had had once seen a 6ft snake swimming in the middle of the Regent's Canal. Despite this species often being found in the vicinity of fresh water in Europe the Aesculapian Snake, unlike the Grass Snake, is not a species that is known to readily take to water unnecessarily, but does on rare occasion. LINK.  In other European countries, such as France, where the Aesculapian Snake is considered native, the typical range for a male specimen is around 1.14ha, however males have been known to travel distances of 2km in search of females during the mating season. Likewise females can travel similar distances in search of suitable egg-laying sites too. Early results in June & August 2021, from the ongoing radio-tagging of Aesculapian Snakes in Wales by Tom Major, has shown that these snakes move about a great deal. Those specimens being monitored in Wales are proving to spend a lot of time in, under and around buildings, where they're hunting for rodents.

For reference see page 3 here:  LINK 

Adult male Aesculapian Snake at Regents Canal, London, 24th May 2012.

Juvenile Aesculapians are usually pale yellow, with several rows of dark brown spots. They usually display a yellow collar behind their head, making them easy to confuse with juvenile Grass Snakes. However Juvenile Aesculapians can lack the dark collar that is nearly always adjacent to the yellow collar found on Grass Snakes. This yellow collar fades and then disappears as the Aesculapian Snake reaches maturity, unlike Grass Snakes which usually retain this yellow collar throughout most of their life, especially males. Juvenile Aesculapian Snakes also usually have a black mark behind the eye that runs to the neck. After their first winter the young juvenile Aesculapian Snakes quickly take on the adult colouration, but they retain the black eye-stripe for some time.

Like Grass Snakes the Aesculapian Snake is an egg-laying snake and adult females usually produce clutches of 5-20 eggs with 5-11 being common. These eggs are grooved and can be as large as a hen's eggs. 

The eggs hatch after 6-10 weeks, depending on the weather and incubation temperatures. Aesculapian Snake hatchlings are slightly larger than that of a Grass Snake, usually measuring around 15-20cm in length. The hatchlings can vary in size though and have been recorded ranging from 12-37cm in length in Europe. 

In London gravid females have been seen in mid-July and the same specimens have been seen again during the first week of August already having given birth. This puts egg-laying for Aesculapian Snakes in London at the end of July, which is the same as in Continental Europe where the Aesculapian Snakes are considered native.

Adult male Aesculapian Snake, at Regents Canal, London, May 2012.

Slithering along the branches of this tree, the Aesculapian Snake is a very competent climber. They use their strong prehensile tail to grasp a firm grip when climbing or when being handled.

Adult male Aesculapian Snake with a total length of 4 ft 5 inches, including tail. Regents Canal, London 2012.

The London Aesculapian Snake is not as timid as our native Grass Snake and can often be approached for photographs without disturbing it or causing it to flee. They rely heavily on their excellent camouflage and will often remain completely motionless until they are sure that they've been seen. Although usually a shy and secretive species, due to the high levels of human traffic that pass by the London Aesculapian Snakes everyday some specimens have become pretty fearless of human contact. 

There have been several occasions when these snakes have been spotted and filmed crossing both busy pathways and the canal bridges in the middle of the day when there are plenty of people about. There have been three videos posted on-line during 2019 and 2020 of an adult female Aesculapian Snake using a bridge over Regents Canal. It is possible that these are all videos of the same individual snake that has deemed it safer or easier to cross the canal via the bridge, even with people about, than risk crossing the busy canal by water.   

  VIDEO 1 (23rd April 2019)   -  VIDEO 2  -  VIDEO 3

Adult male Aesculapian Snake (Snake 27 on Will Atkins records),  at Regents Canal, London. 11th July 2011.

The snake pictured above was one of two specimens photographed high above the ground, basking in the canopy of a large bush at London in 2011. Aesculapian Snakes prefer slightly warmer temperatures to our native snakes and Aesculapians have been observed most often when temperatures have been between 16 - 25 degrees C, with 20-24 degrees being the favoured range.

Adult female Aesculapian Snake (Snake 7 on Will Atkins records), at Regents Canal, London. 11th July 2011. 

The second of two specimens photographed high above the ground basking in the canopy of a large bush at Regent's Canal, London in 2011.

Adult female Aesculapian Snake (Snake 7 on Will Atkins records), at Regents Canal, London. 11th July 2011. 

In their native countries Zamenis longissimus is considered a generalist predator but this species displays an ontogenetic shift in diet. Neonates and juveniles feed mainly on lizards and juvenile rodents. Occasionally they will also feed on amphibians and invertebrates too. Adult Zamenis longissimus feed almost entirely on small mammals, including mice, voles, shrews and rats, but these non-venomous constrictor snakes have also been known to eat lizards, small birds and eggs if necessary.

Like most snakes the Aesculapian Snake sheds its skin periodically in one complete slough. Apart from a noticeable dulling in colour and pattern, one obvious indication that a snake is due to slough is the clouding over and bluing of the scale covering the eye of the snake as pictured above. This eye-scale will sometimes shed first, and then the rest of the snake's skin will usually shed a few days later as a complete slough.

Do Aesculapian Snakes bite?

Aesculapian Snakes vary in temperament, but they are usually a fairly calm species. Many specimens do not bite even when handled. Some specimens do hiss and strike when handled but this is often with a closed mouth to serve as a warning. Others may make a strike and bite without attempting to inflict any real harm, just to get you to release them. It is reported that sometimes Aesculapian Snakes will inflate themselves in a threat display but this is not something I have witnessed myself. Other specimens can be very defensive though and will quickly bite if handled. I have found female specimens to be more likely to bite if handled, particularly in hot weather.

I must stress that there is no chance of being bitten by one of these snakes unless you try and pick one up! They will always flee rather than confront a human.

The bite marks shown in the both images above were inflicted by defensive adult female Aesculapian Snakes.  This account is by an amateur herpetologist who picked up a wild Aesculapian Snake along Regents Canal in 2016:  

"I spotted a large adult female Aesculapian Snake on the canal's edge, mosaic-basking amidst grass and dead twigs on the ground. Only a few inches of the scales on the middle of the snake's upper body were visible, as the rest of the snake was buried beneath the protection of the surrounding foliage. When I carefully picked up the snake to photograph the head for identification purposes, to my complete surprise, an angry, wide-mouthed head quickly spun round and latched onto my wrist. Having never experienced any signs of real aggression from Aesculapian Snakes during previous encounters, I was very surprised by how intent this snake was in defending itself from what it perceived to be a potential predator. It wasn't just biting me, It was rotating and twisting its entire body around in my hands whilst continuing to clamp its jaw around my wrist. It really meant business! After about 10 seconds it released the grip that its jaws had on my wrist, and it immediately turned its attention to my hand and began biting again. Then released, and then bit again! Then released, and then bit again!

It took me a while to realise that this snake, although drawing blood with every bite, was incapable of inflicting any real harm or pain on me. It had extremely sharp little teeth but lacked the sufficient clamping power in its jaws or the necessary tooth size to do me any real damage. After a few minutes, the snake also came to the same conclusion, and once it also realised that I wasn't actually a threat or causing it any harm it began to calm down. After a while it became quite docile and was content to slither around or just relax in my hands and enjoy the warmth for a while before being released back to the exact spot where it was found."

Although considered completely harmless many colubrid snakes have very slight traces of very mild venom in their saliva produced by the Duvernoy's gland. Studies on Garter Snakes have shown that this mild venom could aid subduing mammalian prey when the snake grasps and holds the prey in its jaws for several minutes. Even though Aesculapian Snakes have tiny teeth, and are incapable of causing any real harm or pain to humans, the small puncture wounds can cause quite a reasonable amount of blood to flow from the wound making it appear to be far worse than the superficial scratch that it actually is. Jonathan Cranfield, of Herpetologic, has commented that this "suggests that there are anticoagulant enzymes at work" from the Aesculapian Snake's saliva.

Read the paper by W & F Hayes here.

These Aesculapian Snakes living in London have made the news headlines many times over recent years but May 2014 saw a series of disgraceful reports by the British media about the Aesculapian Snake colonies found in the UK. These sensationalised and scaremongering stories were full of false information and inaccurate reports with ridiculous claims and headlines including the Daily Star's "KILLER snakes that are capable of crushing small children to death are on the loose in Britain! " the Daily Mail's "London hit by outbreak of invasive eight foot snakes that could kill cats or small dogs!" and the Metro's "Army of 6ft 6in snakes capable of killing young children on the loose in London"

Daily Star      Daily Mail       The Mirror (amended)       UK News Yahoo      International Business Times      Travel AOL      Metro      Hackney Gazette

Less dramatic reports from these news websites:

Camden New Journal      London Live      The Islington Tribune      Express      Independant      Daily Post      Vice (excellent article)

Being classed as a non-native species are the Aesculapian Snakes likely to be removed?

Despite these snakes posing very little, if any threat, to our native wildlife (excluding mice and young rats) in 2013 the Government agency 'LISI' (London Invasive Species Initiative) decided that these Aesculapian Snakes were a species of concern and called for the snakes to be eradicated in the UK, quoting them as a "Species of high impact or concern". You can download the list of "Species of concern in London". Thankfully LISI didn't rush in to eradicate these snakes and in 2014 it seemed they must have listened to experts who highlighted the low risk these snakes represented to native species. LISI responded to the sensationalized media stories run by the press at the time and released the following statement alleviating any unnecessary fears and stating that they had no immediate plans to remove these snakes from the wild, at least until further studies of their impact on native wildlife have been carried out. However as of 2023 ZSL have shown no interest in allowing formal studies of these snakes with the grounds of London Zoo, and Natural England have refused to grant any licences to study the Asesculapian Snakes in London.

 Killer snake headlines debunked

"There have been some interesting headlines over the weekend regarding Aesculapian snakes in London, such as the Daily Mirror’s ‘Colony of killer snakes ‘capable of crushing small children to death’ on loose in London’.

The London Invasive Species Initiative (LISI) has put together some information which we hope will clear up some inaccuracies. Below is our original statement, in response to a request for information on their population in London. Note that LISI is not calling for the eradication of the species in London, as reported in some media.

'The species of concern list for the Greater London area has been compiled by a range of industry professionals and land managers within London and is reviewed and updated quarterly. This list does indeed include the Aesculapian snakes that are being referred to, although no action that I am aware of has been taken to remove this population, nor does LISI have any plans to do so at present. This species is listed in the Wildlife and Countryside Act 1981 meaning it is illegal to allow the species to spread or escape into the wild. At present there is limited information on what effects the species may have on our local ecosystems and further information would be hugely valuable in developing appropriate management plans for this population’.

LISI would require further information and monitoring of this species before advising on any further action. With so many other invasive non-native species having a detrimental effect on our environment, it is not feasible to spend limited resources on a species that does not at present seem to be having a significant impact on our ecosystems.

As for the concern about people’s safety, when left alone Aesculapian snakes are a docile and non-venomous species. Please rest assured that your children will not risk being crushed by snakes whilst wandering through central London."

So what does the future hold for the London Aesculapian Snakes?

With many people incorrectly pointing the finger at ZSL being responsible for the escape of the original Aesculapian Snakes that founded the London snake population, in 2016 rather than attempting to remove the snakes from Regents Canal, based purely on my own observations, the action that appeared to have been taken was to lay high numbers of rodenticide bait traps in the areas that these snakes were known to use as feeding grounds. By reducing the available prey for the snakes it would have made it far harder for them to survive.  It's also highly likely that some snakes have been killed as a result of secondary poisoning after feeding on poisoned rodents at Regent's Canal. In May 2020 I was emailed after a member of the public found a dead adult Aesculapian Snake at Regents Canal. The dead snake showed no signs of injury and is quite likely to have died as a result of secondary poisoning. This reinforces my views that at least part of the blame for the dramatic reduction of Aesculapian Snakes at Regents Canal is likely to be due to these rodenticide bait traps used by ZSL. Bangor University have obtained a licence permitting the capture and re-release of the non-native Aesculapian Snakes found around the Welsh Mountain Zoo, as part of their ongoing studies of this species. Sadly ZSL have never been interested in applying for such a licence and Aesculapian Snakes, found within ZSL grounds by ZSL staff over the years, have often been captured and either euthanised or taken into captivity. ZSL have within their collection some dead and preserved Aesculapian Snake specimens that were once caught within their grounds.

3ft sub-adult / young adult female Aesculapian Snake, found on the north bank of Regents Canal, 30th April 2023

Aesculapian Snakes divide the community within the field of herpetology

Whether Zamenis Longissimus belongs in the UK or not has the community divided within the field of herpetology. Some "old school" herpetologists argue that because of their current non-native status under UK law these snakes do not belong in Britain and should be eradicated. Sadly this narrow-minded approach to conservation ignores all the evidence that Zamenis Longissimus is not an invasive species and poses no risk to the ecosystems where they have been introduced in Britain. 

The idea of accepting an introduced species, that hasn’t occurred naturally in the UK for many thousands of years, might be a little difficult for some people to get their head around. In fact the fossilised Aesculapian Snake remains, found at the Cudmore Grove archaeological site in Essex, were also found alongside the remains of Hippopotamus, a species which could also be found occurring naturally in the UK at that time in Britain’s history. Of course reintroducing hippos back into the wild here in the UK would be ridiculous right? So why is the Aesculapian Snake any different? The hippo now only occurs naturally in countries much further south, and thousands of miles from the UK, in areas with a habitat vastly different to that of the modern UK, which it shares with a multitude of species that are not found in our country. This situation is vastly different from the Aesculapian Snake though, which is not only still found in northern France, sharing its habitat with many of the other species currently found in the UK, but until fairly recently Aesculapian Snakes could also be found living as far north as NE Denmark, which is more northerly than any point in England. 

Until these naturalists and herpetologists, that are opposed to the Aesculapian Snakes, can open their minds to accepting Zamenis longissimus in the UK, we don’t stand much chance of getting through to politicians and others in positions of power here. This debate is brought up constantly, on the UK Amphibian and Reptile Groups Discussion Group on Facebook, whenever new sightings of the Aesculapian Snake are shared within the group. Some of these recent debates can be found here:  

12/05/2022     21/05/2022    02/06/2022    03/06/2022    03/06/2022    03/06/2022

During one of these Facebook debates on 4/06/2022, over the Aesculapian Snakes in the UK, Colin Melsom, a former employee of London Zoo during the 1980's, claimed that he was informed at the time by ILEA staff that the snakes released at Regents Canal were collected from southern Italy and were actually Zamenis lineatus, the Italian Aesculapian Snake, rather than Zamenis longissimus. This information is incorrect. One of the obvious and distinctive features of Zamenis lineatus is the copper red, or bright orange iris, a diagnostic feature that is commonly used to distinguish it from the Aesculapian snake Zamenis longissimus. I have been photographing the London Zamenis long enough to say with absolute certainty that none of this colony have ever shown this identifying feature of a red iris, indicative of Zamenis lineatus. Zamenis lineatus also display four dark lines that run the length of its body. Whilst these lines can fade in older specimens when this occurs the colour of the snake also fades and the result is a snake far paler than Zamenis longissimus. All the snakes at Regents Canal are definitely Zamenis longissimus.  LINK    LINK 2

August 2019 - As part of a debate on the future of Aesculapian Snakes in the UK, held on Facebook , world renown herpetologist Dr Wolfgang Wüster made the following comments in support of these snakes:

"I always get a chuckle out of these discussions of introduced species and the supposed threat they pose to natives. The underlying assumption (as in so much of the UK herp conservation scene) seems to be that the status quo, with our native species in the habitats they've always occupied, is still on the menu. Sorry folks, but that is just wishful thinking. Climate change is in progress, and we are seeing more of its effects every year. And while countries sign pious pledges in Kyoto, Paris and elsewhere, a look at the global scene right now (Trump, Bolsonaro etc.) suggests that it would take an unusual degree of optimism to believe that humanity has the collective will and the structures in place to significantly reduce emissions to the levels required to prevent the worst of climate change. We are in for a rough ride.

With climate change as forecast in any of the current humans-doing-too-little-too-late scenarios, not a single global ecosystem will be unaffected. "Nature", in the sense of environments unimpacted by humans, is effectively dead. There's a word for that: the Anthropocene. We are in it, and we are running the show. And since that is where we are, I suggest we would be better off owning it and trying to make the least worst of it, than pretending it's not happening,

For biodiversity, that means that the status quo is not an option. Organisms that can swim or fly will adjust their distributions accordingly under their own steam. It's already happening. Small terrestrial organisms generally don't have that choice in our fragmented landscape. So our options are to do nothing while we pretend that we don't want to interfere with a non-existent nature, while we watch the less adaptable species disappear and Britain's biodiversity decline, without any new diversity coming in to replace what is lost, OR we can decide to manage the situation and maintain overall biodiversity, and that could include welcoming non-native central European species that will now come under pressure in the southern parts of their distributions. The Aesculapian snake (as well as wall and green lizards and other Central European species) are perfect examples of that. They already interact with the same species as our natives in their current native range (so that chances of a disastrous impact are minimal even if they were to spread), and they are likely to end up having a hard time in parts of their native ranges. Why not welcome them here?
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Note that I am ABSOLUTELY NOT advocating a free-for-all! We don't want introduced bullfrogs, corn snakes, Russian ratsnakes, red-eared sliders or other species from the other side of the world to proliferate here. But species from neighbouring regions that would get here anyway but for the Channel? I really think we need to rethink our attitudes there, and take into account the bigger picture of where we are headed."  -  Dr Wolfgang Wüster

1935 32nd Edition, Zoological Society of London guide book

Britain was once part of the natural range of the Aesculapian Snake.  

Fossil remains of Aesculapian Snakes found in Suffolk & Essex

In the UK archaeologists have discovered ancient fossilised remains of Aesculapian Snake at three separate sites, located in both Suffolk and Essex (B.H.S. Bulletin no.50 1994). Fossils at all three sites date back to around the time of the warm end of the Hoxnian stage or the Chibanian stage, during the Late-Middle Pleistocene Period, which ended around 126,000 years ago. - LINK

So although currently considered a non-indigenous species scientists have now accepted that Britain was once part of the natural range of the Aesculapian Snake, when the climate was slightly warmer than it is now, before being driven south by the arrival of subsequent glacial periods. This topic is covered in the 1998 book "Pleistocene Amphibians and Reptiles in Britain and Europe" by Professor J. Alan Holman. Dating of ancient fossils, and DNA analysis of living specimens, has confirmed that the isolated Aesculapian Snake populations in Northern Europe are proof that the range of the Aesculapian Snake has regularly expanded and contracted slowly over long periods of time, when necessary to cope with changes in climate, as the Earth has warmed and cooled. See articles here: 1) Relics Of The Europe's Warm Past - Phylogeography Of The Aesculapian Snake   2) Isolated populations of Zamenis longissimus (Reptilia: Squamata) above the northern limit of the continuous range in Europe.

There remains several isolated populations of Aesculapian Snake, found at sites across Europe today, which are relics of the previous vast range of the Aesculapian Snake, from just 5000 years ago when the climate was warmer than it is today. - See article here: 2005 Action Plan for the Conservation of the Aesculapian Snake (Zamenis longissimus) in Europe - by David Bird & Paul Edgar 

Fossilised remains of Aesculapian Snakes have been found in the UK at these three archaeological sites: 

1) East Farm, Barnham, near Thetford, in Suffolk (discovered in 1994)  -  LINK  

2) Beeches Pit, West Stow, Suffolk (TL798719 discovered in 1991)    

3) Cudmore Grove, Essex (discovered in 1990). 

The British Herpetological Society Bulletin No.50 Winter 1994

In 1998 a book was published by Nick Ashton, of the British Museum, and others involved with the excavation work at the Barnham site, the author went into great detail about the history of, and the finds at, the East Farm site in Barnham, Suffolk: "Excavations at the Lower Palaeolithic Site at East Farm, Barnham, Suffolk 1989-94.- British Museum Occasional Paper 125.".  In this book it was revealed that the fossilised remains found at the Barnham site were widely accepted to date back to "OIS 11, between 364 and 427 ka BP".  The "OIS" are marine oxygen-isotope stages, or oxygen isotope stages, and are alternating warm and cool periods in the Earth's paleoclimate. The abbreviation "BP" means before present date. This dates the Zamenis longissimus fossils at the Barnham site to between 362,000 and 425,000 years BC, or approximately 364,000 and 427,000 years before now. Other dating methods used to date the fossils from the Barham site in 1998 indicated a minimum age of 300,000 years before present. During this warm inter-glacial period the land-mass of the UK was still joined to mainland Europe, and the Aesculapian Snake, and many other wildlife species, would have been able to expand and contract their natural range as the rising and cooling temperatures of the Earth dictated. - LINK

One might consider the possibility that these UK fossils are the remains of ancient feral populations of Aesculapian Snake, that either escaped from captivity or were deliberately released, as it is often reported that both the Greeks and the Romans kept Aesculapian Snakes in their temples for healing and fertility rituals. However, the Mycenaean civilisation of early Greece (1600BC - 1100BC) never made direct contact with Britain and the Romans did not come to Britain until 43AD, so if the fossils are dated correctly then this hypothesis can easily be ruled out as these fossils date back way further than either of these times.

Purchase "Pleistocene Amphibians and Reptiles in Britain and Europe" by Professor J. Alan Holman. 

The Aesculapian Snake is an ancient species of Old World Rat Snake. It is believed that the Aesculapian Snake first appeared on the Earth as far back as 3.2 - 4.9 Mya (3,200,000 and 4,900,000 years ago), based on fossil records from Poland. - LINK

The range of the Aesculapian Snake once stretched as far north as NE Denmark, which is further north than any of he Aesculapian Snake populations now found in both Wales and England. In fact the previously native Zamenis Longissimus colony in NE Denmark was further north than Edinburgh! Until around 6500 BC mainland Britain was joined by land to the European mainland allowing Aesculapian Snakes to travel north and extend their range as necessary when the climate warmed up. So why wouldn't this species have also once been resident in the UK as well?

Whilst Britain focuses its conservation efforts and reintroduction programs on other species, including the Sand Lizard, Natterjack Toad and Pool Frog, at sites across the UK, why are we not doing more to protect the well established and naturalized populations of Aesculapian Snake in the UK? And worse still why are government agencies even considering their deliberate eradication if this species was previously found in Britain anyway, and is not only critically endangered in much of its native range across Europe, but is currently also spreading its range further north once again as our climate warms?

Should these current introduced British populations of Aesculapian Snake therefore, whether intentionally released or accidentally escaped, now be considered as a reintroduction success story of a lost reptile species now returned to Britain once again? With many specimens of the London population of Aesculapian Snakes having already been poisoned, or captured and taken from the wild by reptile collectors, isn’t it about time this species was afforded the same level of protection by UK law as our other rare herpetofauna?

The fossilised remains of Aesculapian Snake that were found at the Cudmore Grove site in Essex, were one of 14 species of herptile found there. Seven of these species are no longer present in Britain but can still be found in Continental Europe. This further supports the evidence of a once warmer climate in Britain, more suited to Aesculapian Snakes and other herpetofauna. With so many other reptile and amphibian species also being found at the Cudmore Grove site this also supports the evidence that Aesculapian Snakes were one of many species of native reptiles and amphibians that could be found living in the area at that time rather than Aesculapian Snakes being an introduced species from captive specimens brought in from ancient Greek or Roman settlements. In fact all three sites where Aesculapian Snake fossils have been found in the UK also contained fossilised evidence of other species of herptiles that are now only found in Continental Europe.  LINK

Although the fossilised remains of Zamenis Longissimus can confirm that this species was once living naturally in the UK, as part of its extended range, palaeoherpetologists are not able to tell exactly when the last of this species died out here. As the last glacial period, the Devensian, started to take hold of Britain, around 33,00 years ago, our reptile species were pushed south as the temperatures dropped. Although most of south-east England would not have been covered in ice this part of England would still have been under periglacial conditions, which were highly unsuitable for species such as Zamenis Longissimus. As the warmer temperatures arrived the current Holocene interglacial phase was initiated, around 11,500 years ago, Britain started to rapidly warm again, and those reptile species that had retreated south, and had managed to cling on and endure the glacial period, were then able to spread north and recolonise areas that were previously frozen. It is not known when the last colonies of Aesculapian Snake were found in the UK but if Zamenis Longissimus were found in the UK, as recently as the previous interglacial period, then they did not survive the drop in temperatures and were clearly unable to recover their previous range after the last glacial period. Those Zamenis Longissimus found in France, that had retreated south during the glacial period, were now only able to spread north as far as the English Channel and their extended range that once ran into England was now lost forever.  LINK

On 21st May 2022 the palaeoherpetologist, Mike Boyd, wrote in the ARG-UK Facebook group:  "What I can say is that the occasionally-quoted date of 10,000 radiocarbon years ( = 11,700 'real' or solar years) ago is certainly incorrect. That is the date of the end of the Pleistocene Period and hence of the end of the Last (Devensian) Glacial Stage. Any Aesculapian Snakes living in Britain during the preceding Last (Ipswichian) Interglacial would have been 'pushed' southward as the ice-sheets of the Devensian Glaciation (whose maximum was between 24,000 and 18,000 years ago) advanced and eventually reached a line running from the Wash to South Wales. Most of south-east England would not have been ice-covered but would have been under periglacial conditions. I cannot imagine Z. longissimus surviving. So the species probably last became extinct in Britain some 20,000+ years ago. I say "last" because there is fossil evidence of Aesculapian Snakes recolonising Britain in earlier Interglacials and (we may assume) becoming extinct here in the alternating Glacial periods."

It is my hope that one day Natural England, and our Government, will no longer consider the Aesculapian Snake to be a non-native, and potentially invasive, species but instead will embrace it as a returned species once native to the UK and afford it the same level of protection under UK Law that our other rare reptiles benefit from.

Does this mean that we should reintroduce all species that were once found in the UK? No, definitely not. Other species that were once found in the UK would no longer integrate into Britain’s current ecosystems without disrupting their delicate balance. In the UK the Aesculapian Snake has found its place in two current ecosystems, where it can both thrive and fully integrate in harmony with its surroundings. If Aesculapian Snakes were to become widely established once again in Britain they would not become an apex predator but would simply become another piece of the food-chain for local ecosystems.  Having Aesculapian Snakes in areas inhabited by humans can actually be a benefit to man as they would serve as a beneficial response to counteract the increase in mice and rats that are now often found in abundance around human habitation, which is a direct result of man’s behaviour. Due to the lack of suitable Aesculapian Snake habitat in the UK it would be highly unlikely that this species could ever become common in the UK once again. However it could, if allowed, form healthy colonies at certain sites across the UK, where there are ideal conditions.

The Aesculapian Snake even features on Wikipedia's list of "Extinct Animals of the British Isles".

Sadly as the current UK Law stands any species that wasn't present in Britain after the end of the last glacial period, around 11,500 years ago, and hasn't subsequently arrived here of its own accord, without accidental or deliberate intervention from humans, is considered to be a non-native species. Although this is bad news for the Aesculapian Snake in the UK it does open the door to the possibility of licenced reintroductions of Moor Frog, Pool Frog, Agile Frog and European Pond Turtle at some stage in the future. All of which were once found native in the UK well after the end of the last glacial period.

This map shows the range in 2020 for Aesculapian Snakes across Europe. See detailed ICUN Red List map here.  See also European Environment Agency Map

The Aesculapian Snake is one of four species of Rat Snake currently found in 31 countries across Europe. It is known that their range once reached far further north than it does now when the Earth's climate was warmer. Some suggest that this vast range may have been contributed to by escaped specimens from when the Romans kept Aesculapian Snakes during the Roman occupation of Europe. Although some herpetologists claim that there is little or no truth behind the "myth" that the Romans kept Aesculapian Snakes, other historians claim that not only were the snakes kept in temples for rituals and ceremonies but they were also kept in homes as "house snakes" to serve as vermin controllers. (see link here)

In the last 150 years Aesculapian Snakes have gone extinct in five northern countries with Denmark previously being the northern most part of their range until around 1863 when the last of the Aesculapian Snakes in that region died out.  Article 1  &  Article 2. 

DNA testing of preserved specimens of Aesculapian Snake collected from Denmark in the early 19th Century have confirmed that these Danish Aesculapians were part of an extended range of snakes, originating from the Balkans, rather than being introduced specimens. The Southern Balkans were a glacial retreat for many reptile species during the ice-ages. And we know that Aesculapian Snakes were present in Denmark from at least 7500BC right up until 1863. See article here: Centuries-Old DNA from an Extinct Population of Aesculapian Snake (Zamenis longissimus) Offers New Phylogeographic Insight - by Morten E. Allentoft, Arne Redsted Rasmussen and Hans Viborg Kristensen

Albino and Melanistic Specimens

Both albino and melanistic specimens of Aesculapian Snakes have been found living in the wild in Austria, Slovenia Bosnia & Herzegovina and Italy but these are incredibly rare. However melanistic specimens are not uncommon in the pet trade. There are no records of any such specimens ever being found wild in the UK. In Greece grey morphs of the Aesculapian Snake can also be found. Striped specimens have been found in Pavia, Italy. In Serbia , where their is huge variation in the appearance of Aesculapian Snakes, axanthic / melanistic specimens can be found. Serbian Aesculapian Snakes vary from light to dark morphs, as well as yellowish or even greenish specimens. Specimens exhibiting feint longitudinal stripes have also been found in Serbia.

1) Read 2003 article on first Albino specimen in Slovenia here.    2) Read 2018 article on Albino specimens in Slovakia here.   

3) Read account of striped specimens found in Pavia, Italy.    4) See axanthic / melanistic specimen from Serbia, April 2022.

In 2013 an incredibly rare amelanistic Aesculapian Snake was found in a garden in Austria. It was taken into captivity and is held at the Reptilienzoo Nockalm, in Austria. This image was shared on the "Zoochat" forum. Other photos can be found here on Flickr. Amelanism is similar to albino, however in amelanism there is a complete lack of dark colour pigments as oppose to a total lack of all colour pigments found in true albinos. An account of the history of this snake written in German can be found here. And videos of this snake can been seen here:   LINK 1   LINK 2   LINK 3

In 2014 a wild hypomelanistic colour morph of the Aesculapian Snake was also found in Austria. This specimen was partially lacking black pigmentation and is the only specimen of its kind ever seen in the wild. One photo was taken before the snake escaped. The story was run by Krone Multimedia. See link here.

In 2014 a wild albino Aesculapian Snake was found in the town of Teslić in Bosnia & Herzegovina. The snake was 900mm in length and was found at an altitude of 220m above sea level. To date this was only the 10th albino specimen of Aesculapian Snake ever to be found in the wild in Europe.  See link here

On 3rd May 2022 Anton Sokolov found two Axanthic Aesculapian Snake specimens, in south-eastern Bulgaria. These rare and unusual specimens lack the yellow pigment in their colouration. See photos: LINK 1    LINK 2

Where can I find wild Aesculapian Snakes?

Inaturalist.org shows records of sightings across Europe including some from both Wales and London.  inaturalist.org

ARC Trust also shows approximate records for sightings in Wales here: Wales Online Amphibian & Reptile Atlas

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This project seeks to develop a widely applicable model system for early invasive species assessment and control planning that will benefit invasive species control efforts in the UK. Through the monitoring of their movements and habitats, the data on snake behaviour and habitat use will feed into an integrated removal plan for the species and contribute to preventing further range expansion and invasiveness. The project began in October 2017 and will continue until October 2021. Snakes will be implanted with radio transmitters between April 2020 and September 2020, and again April 2021 until September 2021."  

Lastly, I would like to make an appeal  to anyone considering catching and keeping a wild Aesculapian Snake as a pet. PLEASE DON'T!  It is an absolute joy being able to find, photograph and watch these beautiful reptiles living wild and free in the UK. They have found a niche in London's ecosystem that has allowed them to flourish without upsetting the delicate balance of our environment. It was once suspected that there could be a maximum of 20 breeding pairs in the London population but numbers are now believed to be much lower. Just removing one snake could have serious consequences for the future of this species in London. Some of these snakes have already been caught, and with the high number of rodent traps being used in the area, loss of habitat, and lack of egg-laying sites, these issues are also likely to have a very negative impact on the number of these snakes along Regents Canal. The Aesculapian Snake specimens currently found at Regents Canal are not escapees or introduced specimens. The originally released specimens would have all died off many years ago. All the snakes found at Regents Canal now were born wild and free on the banks of Regents Canal, and to take them into captivity would be extremely cruel.

Please just be grateful if you are lucky enough to see one, let it live in peace in the wild, and let other people also experience the joy of seeing them living wild in the UK.

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