Slow worm

Although it looks a bit like a snake, the slow worm is actually a legless lizard


Order: Squamata

Family: Anguidae

Species: Anguis fragilis

IUCN Status: Near Threatened

Population Trend: decreasing

Distribution:  Found throughout UK, including Jersey, Guernsey, Herm and Jethou in the Channel Islands.  Not found in Northern Ireland, Scottish islands and the remaining Channel Islands (Alderney, Sark, Lihou and Brecqhou).  Found in much of Europe, except Ireland, northern Scandinavia, central and southern Iberia, most islands of the Mediterranean and Greece.  Also northeastern Turkey, northern Iran, Armenia, Azerbaijan, southern Russia and Georgia. Widespread in the forests of northern Eurasia.

Habitat:  Grassland, moorland, heathland and woods.

Life-span:  Usually up to 20 years (over 50 years on rare occasions).

Size:  Adults up to 50cm long.  Weight: up to 100g.

Description:  Have a shiny look to them.  Males are grey-brown without stripes (though some have bluish spots), while females are brown, with dark sides and sometimes dark stripes running down the back and sides of the body.  Both have grey to bluish bellies. Young slow worms are only about 7-10cm long and very thin, with gold or silver sides and dark bellies.

Food:  Slugs, snails and other slow-moving invertebrates.

Slow worm habits

The slow worm’s scientific name Anguis fragilis means ‘fragile snake’, but in fact they are not snakes at all, they are legless lizards.  The reason they are referred to as fragile in their name is that they have the ability to shed their tails if caught by a predator. The tail continues wiggling, hopefully distracting the would-be predator and allowing the slow worm to make its escape.  Sometimes you can see stumpy slow worms who have had to used their emergency escape trick. Whilst the tail does regrow, it is no longer detachable. Slow worms are also distinguishable from snakes because they have eyelids and ear openings.

Adults emerge from hibernation in late March, with breeding taking place in April and May.  It is rare to see slow worms basking in the sun. Instead, they prefer to hide under something that will heat up in the sun, like a sheet of corrugated iron or a rock.  They will also hide in the warmth of a compost heap.

Slow worms mate for up to ten hours at a time. Females incubate their young within egg sacs inside their bodies and ‘give birth’ to live young towards the end of the summer.  Autumn is spent feeding in readiness for hibernation, which runs from November to March. It takes up to eight years for slow worms to reach their full-grown size.  They have to shed their skins at regular intervals throughout their lives.

Photo by Sam Rowley.

Slow worms and humans

Although their snake-like appearance means that people are often scared by slow worms, especially if they turn up in someone’s garden, they are in fact harmless to humans and do gardeners a favour by eating lots of slugs, snails and other slow-moving garden pests.

The lock down in 2020 is thought to have been beneficial for slow worms. They are often disturbed whilst mating during May as this is a long process for them. With fewer people around outside as a result of the lock down, it's hoped that slow worms will have had more time to themselves and, thus, a chance to breed more easily. 

Protecting the slow worm

Slow worms are protected by law in Great Britain, meaning that they cannot be deliberately killed, injured or traded in any way.  Its numbers are thought to be in decline in the UK and it is a ‘Priority Species’ in the UK Biodiversity Action Plan.

Photo (below) by Nick Goodrum.


Photos by Nick Goodrum and Sam Rowley are courtesy of Wildscreen Exchange.

Factsheet created 01/08/2018.  PL.

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