I am lucky enough to be able to spend time surveying for reptiles, and Slow worms (Anguis fragilis) are undoubtedly the species I come across the most often. These fascinating creatures can be varied and beautifully marked. Unlike some of the UK’s rarer reptiles that utilise quite specific environments, Slow worms take advantage of various habitats. These include urban settings. Slow worms are one of three lizard species native to the UK and are attracted to areas with plentiful grass and compact ground cover, including gardens. They are also commonly found in woodland glades, meadows, heaths, scrub and road verges.

Male Slow worm (above) showing light colour and plane markings. Females (below) are usually darker with contrasting dark flanks and stripes.

The best time to see a Slow worm is from late spring to early autumn when they are most active at dusk. Unlike some of our other species, they prefer not bask openly during the day but can occasionally be seen doing so. Slow worms prefer to take refuge under objects that provide warmth. Slow worms can also be attracted to artificial refugia for ecological surveys. By providing wilder unkept areas like log piles and compost heaps, you can offer Slow worms a place in your garden.

A beautifully marked female Slow worm above.

Slow worms are not snakes or worms but legless lizards. Many lizard species around the world, including relatives of the Slow worm, also lack legs. While these reptiles are unique in the UK in this respect, this characteristic is not uncommon on a global scale. Slow worms are thought to live up to thirty years old in the wild. If you spot a reptile in your garden, you can determine whether it is a Slow worm rather than a snake by observing a few key features. Slow worms have eyelids and can blink, while snakes do not have eyelids. Additionally, Slow worms have a notched tongue, unlike the forked tongues commonly found in snakes. Another distinguishing feature is that Slow worms lack a distinct neck, so their heads do not appear separate from their body.

A male Slow worm showing some blue spots above.

Young Slow worms have golden coloured backs with a black stripe down the middle and glossy black sides. Male Slow worms are greyish-brown sometimes with blueish spots while females are a browner with dark sides. They can have attractive patterns and fine spotted markings but are overall fairly plain and lack the contrasting zig-zag patterns of the Adder (Vipera berus) or the yellow head markings of our Grass snake (Natrix natrix).

A Grass snake on the left showing the yellow head markings and Slow worm on the right.

Many snakes have keels on their scales, which make them feel rough to the touch, whereas Slow worms do not have this characteristic and so they feel much smoother. This smoothness is likely related to the Slow worm’s burrowing behaviour, snagging scales would hinder their ability to move backwards in underground tunnels.

By October, Slow worms begin tunnelling underground to hibernate, which usually occurs between November and March when adults then emerge from their hibernation sites. Breeding occurs during April and May. Slow-worms are ovoviviparous, meaning their eggs hatch while still inside the female’s body, they then give birth to live young which are usually not much more than four centimetres long. This method of reproduction is advantageous in cooler climates, as it allows better control of the temperature of the embryos. Female Slow worms sometimes have scars from bites received by the males during mating, which usually take place in May. They can give birth to up to twelve neonates, typically in August or September.

A juvenile Slow worm showing golden back and contracting dark sides.

Slow worms prey on various invertebrates, including slugs, snails, spiders, and earthworms. Their backward-curving teeth are well suited for grasping prey. Slow worms are conversely preyed upon by several animals, such as Adders, Hedgehogs (Erinaceus europaeus), Badgers (Meles meles), birds and domestic cats. The smell of their faeces is strong enough to deter some predators but if that does not work, Slow worms can detach their tails. The discarded tail thrashes around distracting the predator and allowing the Slow worm to escape. Many lizard species have this ability but Snakes do not. The tail can be regrown; however, the new tail is usually much shorter than the original and cannot be detached again.

The Ecology of Slow Worms in the UK

Slow worms (Anguis fragilis) are legless lizards often mistaken for snakes.

Identification

Slow worms are 35-50 cm long with smooth, shiny skin. Males are lighter sometimes with blue spots, while females are darker with dark sides.

Habitat

They thrive in grasslands, heathlands, woodland edges, and gardens. Slow worms favour areas with dense vegetation for cover and sunny spots. They are often found under logs, stones, or in compost heaps.

Distribution

These lizards are widespread across the UK, particularly in southern England. They are absent from most Scottish islands, Northern Ireland, and the Channel Islands.

Behaviour

Slow worms are ectothermic, relying on external heat sources to regulate their body temperature. They are active from March to October, entering a dormant state known as brumation in winter.

Diet

Their diet mainly includes invertebrates like insects, spiders, and slugs, helping control garden pests and maintain ecological balance.

Interesting Facts

• Tail Autotomy: They can shed their tails to escape predators.
• Mating: Males are aggressive during the mating season, which begins in May.
• Reproduction: Females give birth to live young, typically around eight offspring, in the summer.

Slow worms are crucial for the UK’s biodiversity. Their presence in gardens and natural landscapes indicates a healthy ecosystem.

Richard Ford – Digitalwildlife.co.uk

Acknowledgements

The Wildlife Trust – https://www.wildlifetrusts.org/

Amphibian and Reptile Conservation (ARC) – https://www.arc-trust.org/

Frog life  – https://www.froglife.org/

All photos Copyright©  – Richard Ford © Digitalwildlife.co.uk