A foreign snake species has begun breeding in the countryside once again after being introduced to the UK half a century ago. Researchers in North Wales believe the Aesculapian Rat Snake – which can reach up to 6ft in length – has a stable population in the Colwyn Bay area.
However it is believed the snakes, more commonly found in southern Mediterranean and Balkan countries, are struggling with the climate in Wales, according to Bangor University PhD student Tom Major – who has been studying the non-venomous snake for five years. They are reluctant to cross roads, limiting their range, and are finding it difficult to catch prey – typically rodents up to the size of rats.
“We found a snake yesterday that was born around September 2018 and that weighed eight grams in 2019,” Tom said. “Three years later, it weighed 15 grams – about the same as an HP pencil, reports NorthWalesLive.
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“Even allowing for six months of hibernation each year, and the cooler climate, it’s an extraordinarily slow growth rate. It suggests it might have eaten just once or twice in the past three years.
The Aesculapian Rat Snake arrived in Conwy during the mid-1960s when Robert Jackson, founder of the Welsh Mountain Zoo, imported reptiles from Italy. In the early 1970s, baby snakes were found in the zoo grounds and were initially thought to be grass snakes due to their yellow markings.
Later confirmed as Aesculapian snakes, by then they’d already started breeding and spreading – very slowly – beyond the zoo. Some conservationists have welcomed their arrival as a “returning” species – they were once native to Britain before the last Ice Age, and are not considered harmful.
In 2010, a second, smaller population was found to be living on rats along Regent’s Canal near London Zoo. Just two years ago a third population was reported in Bridgend, though confirmation has proved elusive.
The Colwyn Bay colony is thought to be the UK’s largest – Tom estimates around 70 adults and 120 juveniles. In southern Europe, Aesculapians can reach two metres in length, making them one of the continent’s largest snakes.
While they are Britain’s longest snakes, in colder North Wales where there is more rain, Tom suspects they are unlikely to grow much more than 1.5 metres. The discovery might worry some people, but Tom says there is little cause for alarm.
“On the continent, the snake co-exists with all other species, including animals you find here such as badgers, stoats and domestic cats,” he said. “For a naturally balanced ecosystem, diversity is usually a good thing. It is used to living alongside humans and there is little or no evidence of it causing any harm.”
Despite this, the snake is a Management Priority Species for Wales. The Colwyn Bay population has been monitored since 2004 so that “rapid response can be taken if necessary”, said the North Wales Wildlife Trust.
Tom, whose research is sponsored by the Welsh Mountain Zoo, began with field surveys. Last year he started radio tracking nine snakes and will be repeating the exercise this summer.
“We learnt they have a limited range, moving up to 500m per day, and are often constrained by things like roads,” he said. “They spend long periods hidden in hay bales and in the walls of buildings.”
Generally, they do not avoid humans. They can found in gardens and sheds, though they prefer old stone walls, derelict buildings and ruins. Often, they lay their eggs in garden compost heaps and revisit the same safe places to seek refuge.
And as they feed on small rodents such as rats, the snakes tend to stay close to areas where populations are high – typically where people live.