Slow Worm
Anguis fragilis (Linnaeus, 1758)

Family: Anguidae - Glass and Alligator Lizards

Order: Squamata - Lizards and Snakes

Class: Reptilia

Phylum: Chordata - Vertebrates

Kingdom: Animalia

Red List status: Not listed

Slow worm, male. Buckinghamshire, United Kingdom

Total length: 500 mm

RANGE

Throughout Europe except for the southern Iberian Peninsula and southern Greece, and east as far as western Siberia and Iran. It is commonly absent from islands through much of this range, and is not found in Ireland or many Mediterranean islands. It is absent from much of Europe's far north, but is the only reptile found in the Outer Hebrides.

            Range            Description            Habitat            Behaviour            Biology            Taxonomy            References
Other common names: Blind worm

 

DESCRIPTION

This is a large, limbless lizard that ranges from grey to copper-brown above, and sometimes brick red in females. The body is rounded and slender, more so in males than females. The black sides of the flanks give the latter a rather angular appearance; in males, the flank colouration is the same as the dorsal colour.  Males are longer than females, with larger heads and a more distinct neck. In both sexes, the snout is blunt. Males are usually unpatterned above, while females possess a single, slender black mid-dorsal stripe that runs the length of the body and tail, and blackish flanks. The side of the head is also black in females. Adult males occasionally develop blue spots on their backs and flanks, although the frequency with which this occurs varies with population and subspecies (see Taxonomy). The underside is dark blue-grey in males and black in females; in males black mottling may be present. The smooth scales give the animal a shiny appearance, and are larger on the upper surface than the flanks. The tail is longer than the body in intact specimens, though regenerated tails are much shorter.

 

Female slow worm. Note the darker flanks and vertebral stripe.

Male slow worm.

Juvenile colouration ranges from pale gold or greenish through to light brown, and as in adult females a mid-dorsal (vertebral) stripe is present. In males this gradually fades as the animal grows.

 

Similar species: Limbless lizards are frequently confused with snakes, but unlike snakes the slow worm possesses a visible ear and has eyelids. The tongue is short and notched, but is not forked. Throughout most of its range the slow worm cannot be mistaken for any other lizard due to the absence of limbs. In southern Greece, it is replaced by the similar Peloponesse slow worm (Anguis cephalonica), which can be distinguished by differences in colouration and by having 34-36 mid-body scale rows (24-30 in the slow worm). The European glass lizard (Ophisaurus apodus) is larger and has a distinctive groove along each flank. Worm lizards, family

                                            Amphisbaenidae, have rings of scales around the body. Three-toed skinks have rudimentary

                                            forelimbs; limbless skinks are smaller, have more pointed snouts, and 18-20 mid-body scale rows.

Slow worm head. Note the ear, visible as a depression.

HABITAT

Dry, open areas with large amounts of ground cover. The slow worm is consequently a common resident of abandoned 'brown-field' sites in urban areas, and can also be found in parks, gardens, heath, and woodland verges or clearings. Within these habitats, slow worms tend to seek out damper, but not wet, areas.

Elevation: 0-2,400 m

 

BEHAVIOUR

A fossorial species, usually burrowing within loose soil or hiding beneath vegetation and other cover objects. Animals only rarely bask in the open (gravid females bask more often than other individuals), preferring to rest beneath warm cover objects such as rocks or metal sheeting, where they can often be found in high densities. Animals are most active at around 15C, often in the early evening or around dawn. Animals generally aggregate at hibernation sites, sometimes with other reptile species - in Britain, hibernation lasts until March or April.

Diet: Soil invertebrates, including snails, slugs, earthworms and insects. Occasionally small reptiles are taken.

Courtship behaviour: Animals contend for females in physical combat, wrestling or biting their rivals. Successful males grasp females behind the head in their jaws, and may intertwine their bodies and tails while mating.

 

BIOLOGY

Breeding biology: Slow worms give birth to live young, and litters of 3-26 (generally 6-12) juveniles are produced 2-3 months after mating. Newborn young are 60-100 mm long. Females breed once every other year. Animals become sexually mature when around 300 mm long; 3-4 years in males, 4-5 in females.

Lifespan: Slow worms are among the longest-lived lizards, with one record of an animal surviving in captivity for 54 years. In the wild, they are likely to live up to 15 years.

 

TAXONOMY

Two subspecies are recognised, with Anguis fragilis colchinus occurring eastwards from Hungary. This form is typified by having 26-30 mid-body scale rows (24-26 in A. f. fragilis, the western form), and blue spotting in males is more common. Intermediate populations exist in a zone running from western Finland to southern Hungary.

 

REFERENCES

Arnold, N. and Ovenden, D. (2004) Collins Field Guide: Reptiles and Amphibians of Britain and Europe HarperCollins, London: 288pp

Wareham, D.C. (2008) The Reptiles and Amphibians of Dorset British Herpetological Society: 120pp

Anguis fragilis, female. Buckinghamshire, United Kingdom