Slow Worm (Anguis fragilis): Europe's Legless Lizard

Is the slow worm a snake?

No. The slow worm is a lizard that has lost its legs during evolution. Its closest relatives are other members of the family Anguidae, such as the glass lizards of North America and the European glass lizard of the Balkans, not snakes.

Several features give it away. It has movable eyelids and can blink, which no snake can do. It has small ear openings, though these are usually hidden under scales. Its tongue is short and only notched at the tip, not long and deeply forked. It can shed its tail to escape a predator, and inside its body it still has tiny remnants of shoulder and hip bones. Our guide is a slow worm a snake? explains how to tell it apart from adders and grass snakes.

Appearance: shiny scales and gold juveniles

The slow worm has a smooth, glossy, pencil-shaped body with no visible neck. The head runs straight into the body, and the body runs straight into a tail that is often slightly longer than the rest of the animal. Under the scales lie small bony plates called osteoderms, which make the body stiffer than a snake’s and give the slow worm a rather rigid, wriggling way of moving.

Adults are gray, brown, bronze or copper above, with a dark gray to black belly. Males are usually more evenly colored and often grayish brown. Some older males have scattered bright blue spots, a feature that is more common in the closely related eastern slow worm. Females are usually brown with darker sides and often a thin dark line down the middle of the back.

Newborn slow worms look very different. They are thread-thin and gleaming gold or silver above, with a black belly and sides and a dark stripe along the back. Many females keep some of this juvenile pattern into adulthood.

How big do slow worms get?

Most adult slow worms measure about 35–45 cm (14–18 in) when their tail is complete. A few exceed 50 cm (20 in), and the longest on record reached about 57 cm (22 in). The head and body make up less than half of this, about 12–22 cm (5–9 in), and the rest is tail. Many adults are shorter because they have lost part of the tail. The heaviest and longest individuals are usually females.

Habitat and range

The slow worm lives in western, central and northern Europe and the western Balkans. Its range runs from northern Spain and Portugal through France, the Low Countries, Germany, Switzerland and Austria to the western Balkans, and north to Great Britain, Denmark, southern Norway and southern and central Sweden. In the Alps it reaches about 2,100–2,400 m (6,900–7,900 ft).

Until about 2010, most European slow worms were lumped into this one species. Genetic studies have since recognized five species in the genus: the slow worm in the west, the eastern slow worm (Anguis colchica) from eastern Europe to the Caucasus and northern Iran, the Italian slow worm (A. veronensis), the Greek slow worm (A. graeca) and the Peloponnese slow worm (A. cephallonica). The western and eastern species meet in a broad zone running roughly through Poland, the Czech Republic, Slovakia, Hungary and Romania.

Slow worms are found throughout much of Great Britain but are not native to Ireland, where only a small introduced population lives in the Burren, as explained in our guide to animals of Ireland.

They like places with dense, low vegetation, some moisture in the soil and plenty of hiding places: rough grassland, heaths, woodland edges and clearings, hedgerows, railway embankments, overgrown churchyards, allotments and gardens. More detail is in where do slow worms live?.

What do slow worms eat?

Slow worms hunt slow-moving prey. Their main foods are slugs, especially small field slugs, and earthworms. They also eat snails, hairless caterpillars, beetles and their larvae, woodlice, small spiders and other insects.

Their eyesight is limited, so they find prey mostly by smell and touch, flicking the tongue to sample scents. Small, sharp teeth curve backward and hold slippery prey, which is swallowed whole. Swallowing a large earthworm can take up to half an hour. Gardeners often welcome slow worms because of their appetite for slugs.

Behavior: hiding, basking and hibernation

Slow worms are secretive and spend most of their time hidden in leaf litter, under logs, stones and tussocks or underground. Unlike most lizards, they rarely bask in the open. Instead they warm up under objects heated by the sun, such as flat stones, wood, sheets of metal or plastic, and compost heaps. Pregnant females are the main exception and bask more often in direct sunlight.

They are most active in the early morning, in the evening and on mild, damp days, especially after rain, when slugs and worms are on the move. Several slow worms often share a good hiding place.

In autumn, usually during October, slow worms retreat underground to hibernate in frost-free places such as burrows, root holes, rock crevices and old tree stumps. They often hibernate communally, typically in groups of about 5–30, sometimes more than 100, and occasionally alongside other reptiles. They emerge again in March or April. Our list of animals that hibernate covers other winter sleepers.

Reproduction and life cycle

Mating takes place from late April to June. Males become aggressive and wrestle and bite rivals. During mating, the male grips the female by the head or neck with his jaws, and copulation can last for hours.

Slow worms are ovoviviparous: the eggs develop inside the mother’s body, and she gives birth to live young. After about 11–14 weeks, usually between mid-July and September, she produces a litter of typically 8–12 young. Each baby emerges inside a thin, transparent egg membrane and breaks free almost immediately. The newborns weigh less than 1 g and are independent from birth. Females often breed only every second year.

Young slow worms grow slowly and become mature at about 3–5 years old.

How long do slow worms live?

Slow worms are among the longest-lived lizards known. A male kept at Copenhagen Zoo lived there from 1892 to 1946, about 54 years, and his age when he arrived was unknown. In the wild, anecdotal reports suggest that some slow worms reach about 30 years, although most probably die much younger because they have so many predators. See how long do slow worms live? for more.

Predators and defenses

Slow worms have many enemies. Badgers, hedgehogs, foxes, polecats, birds of prey, owls, crows, herons, pheasants, adders and smooth snakes all eat them, and domestic cats kill many in gardens. Young slow worms are also taken by thrushes, starlings, shrews, large ground beetles and toads.

When seized, a slow worm writhes, smears droppings and may shed its tail. The broken tail keeps twitching for minutes and distracts the predator while the lizard escapes. The scientific name fragilis, meaning fragile, refers to this. Unlike many lizards, the slow worm regrows only a short, rounded stump, and in some populations more than half of the adults have an incomplete tail.

Conservation status and legal protection

The IUCN Red List classes the slow worm as Least Concern (assessed in 2021). It remains common in much of its range and is the most common reptile in Germany.

Many local populations are declining, however. Threats include building development, intensive farming and forestry, drainage, the clearing of rough, “untidy” vegetation, mowing, road traffic, garden chemicals such as slug pellets, domestic cats and people killing them in the mistaken belief that they are snakes.

In Great Britain, slow worms are protected under the Wildlife and Countryside Act 1981, which makes it illegal to intentionally kill, injure or sell them. Developers whose sites hold slow worms usually have to move the animals to safe habitat before building work starts.

Myths and facts about slow worms

Myth: slow worms are blind. The old names blindworm and blind worm refer to the small eyes, but slow worms can see and can close their eyes with true eyelids.

Myth: slow worms are slow. The name comes from Old English slāwyrm, and its first part is probably not the word “slow” at all but an old word related to Scandinavian names for the animal. Slow worms are not fast, but they can wriggle away quickly into cover.

Myth: slow worms are dangerous. They have no venom and are harmless. The only venomous snake in Britain is the common European adder, which has a zigzag pattern and keeled scales.