Slowworms (sometimes also called “blind worms”) are members of the Anguidae family of lizards, most of which are found in the Americas. Two species are found in Europe, the slowworm being the most common and widespread. Indeed, slowworms are probably the second most widely distributed lizard in Europe.
Despite their name, slowworms are neither worms, nor particularly slow, although their name does derive from the ease with which they can be caught compared with other reptiles. Contrary to appearance, the slowworm is a leg-less lizard, not a snake. Its Latin name means “fragile snake”, owing to its tendency to shed its tail when caught. Two subspecies have been proposed; Anguis fragilis colchicus found in south-east Europe, the Caucasus and Iran and Anguis fragilis fragilis native to Britain and most of Europe, with fossil evidence dating back some 40 million years.
That which follows is a summary of slowworm natural history. The detailed article for this species will follow in due course.
The slowworm at a glance
Size: Adults up to ~50cm (20 in.) long, although typically closer to 35cm (14 in.), and upto 100g (3.5 oz.). Newborns ~6cm (2.4 in.) and weigh upto ~20g (0.7 oz.).
Colour/Appearance: Typically brown-grey in colour with a copper lustre on back. Males tend to be more uniform in colour than females, which often present with dark stripes running length of back and flanks. Males usually lack any striping and may have blue spotting on back and flanks. Newborns striking silver or gold back with black dorsal stripe and black flanks and belly (occasionally red/orange). Dark markings on throats of both sexes appear unique to individual. Melanism and albinism rare. No external appendages and very smooth scales give shiny snake-like appearance. Presence of eyelid (nictitating membrane) and open ears separates them from snakes along with notched tongue, which is broad, flat and pink with blue tip. Tail often truncated where failed to regrow from shedding giving ‘stumpy’ appearance.
Distribution: Found throughout most of mainland Europe from Wales in west to Iran in east, north into southern Norway, Sweden and Finland, south to midland Portugal and Spain; absent from Mediterranean islands and Ireland, excluding a handful of reports from County Clare in the mid-west thought to stem from introductions in 1970s.
Longevity: Long-lived reptile, with reports of at least 54 years in captivity (Copenhagen Zoo). Thought 10-15 years typical in wild, but records exist of up to at least 30 years.
Sexing: Males have broader head cf. females, giving appearance of distinct neck (i.e. narrowing behind head). Colouration can be indicative; females having dark stripes, thin dark line down middle of back in particular, and males often with blue spots.
Habitat: Britain’s most urban reptile. Found in wide variety of habitats from mixed farmland and deciduous woodland to gardens, railway embankments, allotments and city “waste ground”. Also present along sea cliffs and motorway verges. Preference for dense vegetative cover and comparatively damp conditions. Most of time spent in vegetation or under discarded objects such as corrugated iron sheets, tyres, rubber mats, etc.
Activity: Typically hibernate October to March either underground (in small mammal burrows) or dense vegetation. Diurnal like most reptiles. Must bask to raise body temperature, although sometimes found active at temperatures of only 15C (59F). Basking done under cover and seldom found in open unless moving/hunting or (during breeding season) fighting. May take refuge underground (semifossorial) in very hot weather. Females bask more when pregnant. Males fight fiercely during breeding season, wrestling and biting one another.
Territory/Home Range: Males appear to range further than females, although may not be statistically significant. Study on Purbeck in Dorset found largest range used by male was ~800 sq-m (0.2 acre); much larger range of 3,800 sq-m (1 acre) calculated for males in Switzerland. Animals overlap extensively spatiotemporally with no evidence of territoriality.
Diet: Diet composed primarily of invertebrates, molluscs (slugs and snails) and earthworms in particular. Indeed, voracious predators of snails and slugs, particularly Nettled slug (Deroceras reticulatum). Will also take insects and spiders and, occasionally, small lizards or amphibians. Backward-pointing teeth allow securing of slippery prey.
Reproduction: Breeding season runs for April and first half of May. Mating involves male biting back of female’s neck as two entwine hind bodies and tails. Some reports of copulation lasting 10 hours. Females must reach critical length (~30cm / 12 in.) and body condition prior to reproducing, hence typically breed biennially starting at 4-5 yrs old. Males sexually mature at 3-4 yrs old. Gestate for 2-3 months before giving birth to 6-12 (up to 26) live young enclosed in transparent caul. Birthing season mid-August to mid-September. No parental care provided.
Behaviour and Sociality: Generally a non-aggressive species that doesn’t bite when handled. May live at high densities (e.g. >600 per hectare) and hibernate communally. Males can apparently discriminate own scent from that of other individuals of both sexes and spend longer investigating conspecific marks.
Predators: Taken by birds of prey including buzzards, kites, kestrels and, particularly, tawny owls. Foxes, badgers and hedgehogs also reported to take them occasionally as are corvids, storks and larger reptiles, specifically smooth and grass snakes. Common prey of domestic cats and juveniles may be very susceptible to pheasants, although data are lacking.
Threats & Conservation: Threatened by development, although perhaps more resilient than other reptiles given broad habitat preference. Lower level habitat destruction through garden clearance problematic and slowworms vulnerable to traffic. Covered by UK Wildlife and Countryside Act (1981) making it illegal to deliberately kill, injure or sell one, but no special protection offered meaning license is not required to handle or survey. Listed in Section 7 of Environment (Wales) Act (2016), requiring Welsh authorities to maintain and enhance habitat biodiversity for this species.
Britain’s Reptiles & Amphibians - by Howard Inns
WildGuides Ltd. -- 2011 -- ISBN: 978-1903657256
Collins Field Guide: Reptiles & Amphibians of Britain & Europe - by Nicholas Arnold & Denys Ovenden
HarperCollins -- 2004 -- ISBN: 978-0002199643