Slow-worms – Status, Science and News

Reptiles are often associated with hot weather, and with temperatures reaching there height for this year, there have been many sightings during the last couple of months. The UK has six species of native reptile: adders, grass snakes, smooth snakes, sand lizards, common lizards and slow-worms(1).

Slow-worm status 

Although the slow-worm is still found commonly throughout Britain, especially in the South-West, it is thought their numbers are on the decline. A number of things are thought to be contributing to this including climate change and persecution. However, the majority of the blame is being put on habitat loss due to human development(2).

Slow-worm facts and identifiable features Slow-worms are found throughout Britain and are our only legless lizard(1). As ectotherms they cannot create their own body heat and rely on their surroundings for homeostasis. As with all of Britain’s other reptilian species, slow-worms hibernate over winter. They then give birth to live young during the summer(3). The scientific name for the species of slow-worm found in the UK is Anguis fragilis. It is thought the name “slow-worm” comes from the Old English sla-wyrm meaning “slay worm”, referring to its feeding habits4 as they are known to feed on invertebrates such as worms, slugs, spiders and snails(1). They live in areas with plenty of vegetation, stone crevices and holes below ground and are often found in meadows, hedgerows and gardens(3). Slow-worms have a polished-looking, shiny skin with the males being greyish while females and juveniles having a browner colouring. Females will also have a dark brown colour along their sides. They can grow up to 40cm long and can live for several decades(5). How to tell a limbless lizard from a snake? and Why evolve to be limbless? Most lizards, including the slow worm, have visible ear openings and eyelids, unlike snakes. Lizard tails, the part of the body that continues after the cloaca, are longer than their bodies whereas snakes have short tails(6). Lizards are also able to detach their tails as a defence mechanism to distract predators(3), whereas snakes cannot. Being limbless has evolved independently many times within reptiles suggesting that it is a functional and advantageous body plan. It is associated with a burrowing lifestyle6, which gives them access to a food source underground and the opportunity to hibernate underground.   Slow-worms in the news Slow-worms are protected in the UK and this can cause problems when humans and slow-worms wish to inhabit the same area(1). One example, reported by the BBC, in 2013, being a colony of slow-worms inhabiting an area in Cumbria designated for a new roundabout. Around 40 slow-worms were found and moved to a suitable woodland area before construction could begin(7). So what are the rules for building in a slow-worm inhabited area? JRP Environmental, a company that specialise in the management of projects and the benefit of wildlife in the UK, advise that ideally the slow-worms should be protected before planning permission is given. However, if work has begun and slow-worms are discovered all work should be halted and the regional Natural England office should be contacted to carry out a slow-worm survey and to respond with the appropriate conservation measures. These conservation measures usually involve the slow-worms being moved to a suitable area away from construction sites or sites designated for construction, where they can be left undisturbed(3).

Slow-worms in science

Many different scientific studies have been conducted on the slow-worm. The information from these studies has allowed scientists to have a greater understanding of many aspects of slow-worm life, and has allowed for the development of techniques that could potentially help conserve them, and other reptilian species.

A new non-invasive way of analysing reptilian diets

In 2011, the journal Molecular Ecology Resources published a study in which a non-invasive DNA-based molecular diagnosis (454 pyrosequencing) was used to analyse reptilian diets. The specific aim of this study was to determine which earthworm species are fed on by slow-worms. This is important as slow-worms often need to be relocated due to land development and so knowledge of their diet is needed to find a suitable alternative home.

Using this technique, it was found that all species of earthworm are exploited by slow-worms and this lack of specialisation allows them to survive in a wide variety of habitats.

This study also demonstrated the speed, practicality, and inexpensive method of the pyrosequencing of prey DNA, in faeces. This generates valuable ecological information on reptilian diets and has subsequently been used in a number of studies(8).

Using slow-worms as a model organism to analyse nematode preference in reptiles

In March of this year, a paper, published in Molecular Ecology, reported on a study that for the first time used a molecular diagnosis to track nematode parasitism in wild populations of slow-worm. The results of that study show that there is a correlation between sex and time of year in regards to nematode parasitism of the slow-worms. For example, they found a lower nematode prevalence in males than in females in July but a high prevalence in males in April. With further study this information could be used to help conserve the slow-worm and other reptile species (9).

How can you help the slow-worm?

Reptiles are sometimes persecuted due to their dangerous reputation or as their habitat clashes with that of a building project. However, all native reptiles are protected by the Wildlife and Countryside Act of 1981, this law makes it an offence to intentionally kill, injure or sell any of these species. If you witness anyone committing these offences report it to your local police wildlife liaison officer(4).

Having resident slow-worms in your garden can be to your benefit as they eat many common garden pests.
If you want to encourage reptile life in your garden the RSPB recommends a pond, rocks and dead wood as they can provide shelter and places suitable for hibernation. A piece of tin left in a warm but hidden area would also be an ideal basking spot for these ectotherms. If you’re feeling particularly enthusiastic the RSPB has also published instructions on how to construct your very own hibernacula for reptiles(10). Instructions can be found here:

Reference material

(1) The wildlife Trust, Wildlife facts, British Reptiles. Viewed 24/06/2014
(2) Norfolk Wildlife Trust, Species explorer, Amphibians and Reptiles, Slow worm. Viewed 24/06/2014
(3) JPR environmental, slow-worm, slow-worm habitat, ecology, mitigation & the law. Viewed 24/06/2014
(4)  H2h2 Researcher, 2004, The slow-worm. Viewed 24/06/2014
(5) O.S.G. Pauwels, 2011, Slow worm, Arkive. Viewed 24/06/2014
(6) Mike Wall, 2013, Are legless lizards snakes?, live science. Viewed 24/06/2014
(7) 2013, Greenodd slow worm colony moved to new home from roundabout, bbc news, England. Viewed 24/06/2014
(8) Brown, David S., Simon N. Jarman, and William OC Symondson. “Pyrosequencing of prey DNA in reptile faeces: analysis of earthworm consumption by slow worms.” Molecular ecology resources 12.2 (2012): 259-266.
(9) Brown, David S., and William OC Symondson. “Sex and age‐biased nematode prevalence in reptiles.” Molecular ecology (2014)
(10)               2013, Building a hibernaculum, Homes for reptiles and amphibians. Viewed 24/06/2014


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Chloe Brookes


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