- Latin name
- Zamenis longissimus
- Class
- Reptiles
- Group
- Snakes & Lizards
A sister clade to the native smooth snakes (Coronella sp.), Aesculapian snakes are considered an introduced species in Britain, having probably died out at some point during the Cretaceous, around 120,000 years ago. This species has historically been associated with medicine, and particularly with Apollo's son, Asclepius, the Greek god of healing (Aesculapius being the Roman equivalent, meaning "to cut open"). Its image is still featured, entwined with his staff, in medical logos today.
Previously Elaphe longissima, the present binomial is derived from the Greek zamenés meaning "angry" or "fierce" and Latin longissimus, "the longest one".

Size: UK's longest snake species. Adult males, which grow larger than females, may reach just over 2 m (6.5 ft.) long, although individuals usually don't exceed ~1.6 m (5 ft.). Males typically weigh 800-900 g (28-31 oz.) while females are somewhat lighter at 400-600 g (14-21 oz.).
Colour/Appearance: Long, slender snake with a blunt head and round pupil. Adults are typically an olive brown/green, often with a bronze sheen, with a paler patch immediately behind the head that's sometimes associated with a darker V- or U-shaped marking. The anterior section is lighter than the posterior, with the upper surface frequently displaying a white-spotted appearance from white edges to dorsal scales. Underside is lighter than dorsum, pale yellow to white in colour. Juveniles often greenish-yellow in colour, with well-defined dark stripe on side of head, 4-7 rows of dark brown spots along the body, and darker neck marking. Very dark (melanistic), red (erythristic), and albino individuals have been reported from Europe.
Distribution: Two populations in Britain, one in England and the other in Wales. The English population is small (declining?) and appears restricted to a roughly 2 ha (5 acre) area of Regents Canal in vicinity of London Zoo, while the Welsh population is larger and centred around Colwyn Bay in the north. The Welsh population numbers perhaps 150 animals and is descended from at least one escapee (likely several) from the Welsh Mountain Zoo in early 1960s, with first records outside zoo grounds in 1970. Contrary to media reports, the London population, which is perhaps only 40 individuals, is believed to have originated from a handful of animals of Italian origin either having escaped or been deliberately released (official vs. unofficial) from Inner London Education Authority's Centre for Life Studies during the mid-1980s and did not escape from London Zoo. Reports of an established population in Bridgend, ca. 290 km (180 miles) south of Colwyn, in September 2016 were revealed as a mixture of a hoax, and misidentification of grass snakes on local allotments. Sporadic, unconfirmed reports of solitary animals from Dorset and Devon. Widespread in central belt of Europe from central and southern France in the west to eastern Ukraine in the east. South into northern Spain, central Italy, and Greece; north to Austria and south-east Poland.
Habitat: Similar to grass snakes, Aesculapians are an edge species, frequently found at deciduous woodland edges, along field borders, and around pond/river sides. Will also inhabit open meadows, woodland (in which they readily take to the trees) and seem at home in urban settings, even very busy ones such as London Zoo. Seems reliant on woodland canopy for dispersal in Britain.
Longevity: Possibly up to 30 years in captivity, although they're very unlikely to reach this age in the wild.
Sexing: Males longer, but comparatively thinner, while females are shorter and with larger girth.
Activity: Primarily diurnal and active in temperatures above ~15C (59F), may extend activity into dusk and night on particularly warm nights during summer. Tracking data from Wales suggests sporadic activity, with 4-6 days of inactivity/rest followed by 2-4 days of movement, presumably hunting. In Britain, snakes can be found from April through until October, occasionally even November in mild autumns. Hibernates from mid-autumn until early spring. Active temperature range in London appears to be ca. 16-25C (61-77F), with 20-24C (68-74F) preferred. May bite and/or regurgitate food if handled and capable of exuding unpleasant smelling secretion from cloacal glands.
Territory/Home Range: Variable with habitat quality, but both sexes are highly mobile. Males and females may move up to 2 km (1.2 mi.) per day while looking for mates and egg-laying sites, respectively. Male tracked for 95 days (June-September 2021) in Wales moved repeatedly between two areas of activity ~700 m (0.4 mile) apart - most active during June. Female tracked over 61 days in same location and period moved repeatedly between several activity sites, spread across ~1 km (0.6 mi.) and covering ~10 ha (25 acres) - most active in July. In continental Europe, one male was tracked using a range of just over 1 ha (2.5 acres).
Diet: A non-venomous constrictor that, in Britain, feeds primarily on small mammals and birds. London snakes eat almost exclusively brown rats, including pups thus suggesting nest raiding. In Wales, eggs and birds (nestlings and adults) are taken in the nesting season, along with mice, rats and in on case a mole. Reports in the literature of squirrels being taken. Observation of a male snake with the radio-transmitter from a female in its stomach suggests cannibalism. In their native range they'll also eat lizards, newts, frogs, and various insects. In Albania they have been observed catching and eating bent-wing bats in cave roosts. Feed every three days or so during summer.
Reproduction: Sexual maturity is reached at 4-6 years old, around 80-100 cm (~3 ft.) in length. From April, males wrestle for access to females, each trying to push the other down. Male and female will "dance" before intertwining to copulate. Most mating seems to happen during June in Britain. Egg-laying habits are like those of the grass snake, often choosing areas of damp/rotting vegetation as incubation sites, although may also be laid in tree hollows or in the soil. In London, most eggs apparently laid in second half of July. Eggs are comparatively large, 35-60 mm (1.4-2.3 in.) long by 17-25 mm wide (0.7-1 in.), pair shaped with longitudinal grooves in the shell, laid in clutches of up to 20 (typically 5-11). Hatchlings emerge 6-10 weeks later (temperature dependent) at ~20 cm (8 in.) long, perhaps as long as 37 cm (14.5 in.), with appearance similar to hatchling grass snakes.
Behaviour and Sociality: Like all reptiles, Aesculapians must obtain warmth from their environment to sustain biological activities and will bask in temperatures below ~27C (81F); beyond this they seek shade and will cease activity in extreme heat. Climb very well, owing to angled ventral scales, even scaling vertical trunks, and will hunt and bask arboreally. Don't appear to swim as readily as grass snakes. Elsewhere in range it tends to be a shy and secretive species, but those in London have adapted well to human activity and seem less susceptible to disturbance, while Welsh snakes often hunt in and around buildings. Usually solitary.
Threats: Vulnerable to predation by birds of prey (esp. buzzards) and corvids, and remains from Wales suggest small mustelids (e.g., stoats) may take some. Foxes, badgers and domestic dogs and cats probably also predate Aesculapians, but data are lacking. Susceptible to road traffic. Seem dependent on woodland cover for spreading and loss of habitat is likely the reason populations in Britain haven't expanded significantly in the past six decades. In London, council operations such as strimming of grass verges along the canal likely kill/injure some snakes. Some suggestion that use of rodenticides by London Zoo to control rats is both depleting food supply and killing snakes through secondary poisoning (i.e., eating poisoned rats).