Slow worms and development (Updated August 2020)

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The slow-worm (Anguis fragilis) is often mistaken for a snake but is in fact a legless lizard. Slow-worms are fairly widespread in England, Wales and Scotland but they are shy and not often seen as they rarely bask in the open. They are found in a variety of different habitats including gardens, favouring thick vegetation, crevices in rocks and uncompacted soils in which to burrow.

Identification of slow-worms

Slow-worms, often mistaken for snakes, are actually legless lizards. Unlike snakes, lizards such as the slow-worm have eyelids and can detach their tails as a defence mechanism and regrow another although never to the same length. They can grow to a total body length of 45 cm but 30–40 cm is more typical. In those which have an intact tail it will account for over half of their total body length.

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Males and females can usually be distinguished by colour. Males have larger heads than females of the same size. Males are greyer and more uniformly patterned whereas females and all juveniles are browner with a notable demarcation between the dark sides and back and often have a darker dorsal line or narrow zig-zag stripe down the centre of the back. 

Ecology and habitat of the slow-worm

Slow-worms are exothermic (they do not create their own body temperature) relying on warming up by basking in warm areas. Whilst basking, they prefer to be partially obscured or covered by some vegetation, rather than in the open.

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They lead a somewhat secretive life, spending most of their time hidden under vegetation, stones, or in holes below ground. Many different habitats provide suitable features for slow-worms such as woodland rides, tussocky grassland and meadows, hedgerows, heathland, gardens as well as other urban and sub-urban areas. However, slow-worms do not like too much shade as this does not create areas in which to bask.

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Like all the other UK reptiles, slow-worms hibernate over the winter. Slow-worms hibernate from mid to late October to late February or early March depending on weather. They do not lay eggs but give birth to live young, from mid August to late September.

Current status of the slow-worm

Widespread and locally common, especially in the south-west. Considered to be absent from parts of north-west England. They have suffered a slight decline, notably in the East Midlands but severe declines have been reported in parts of Scotland. Slow-worms exhibit the widest habitat preference of Britain’s reptiles and are frequently encountered in urban and suburban environments.

Legislation relating to the slow-worm

Slow-worms are protected against killing, injuring and sale under UK legislation:

• Bern Convention 1979: Appendix III (Bern is European legislation Appendix III Protected Fauna Species)

• Wildlife & Countryside Act (as Amended) 1981: Schedule 5

• Countryside Rights of Way Act 2000 (CRoW 2000)

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Following an amendment in 1988 of the Wildlife & Countryside Act 1981 (WLCA), part of Section 9(1) and all of Section 9(5) apply to the slow-worm’s listing on Schedule 5 of the Act. Consequently, under parts of Section 9(1) slow-worms are protected against intentional killing and injuring but not ‘taking’. Under Section 9(5) it is an offence to offer for sale, transport for sale, advertise for the purpose of trading any live, dead, part, or derivative of, slow-worms. Section 9 applies to all stages in their life cycle.

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WLCA only applies to England, Scotland and Wales it doesn’t cover Northern Ireland, Channel Isles or isle of Man. CRoW relates to England and Wales only.

The maximum fine on conviction of offences is currently £5,000. The CRoW Act amended the 1981 Act to allow for a custodial sentence of up to six months instead of, or in addition to, a fine. Fines may be imposed in relation to each offence committed, so operations involving many animals or repeated offences can potentially accrue large fines.

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In addition, items or equipment, which may constitute evidence of the commission of an offence, may be seized and detained. The CRoW Act also amends the Police and Criminal Evidence Act 1984 to render Section 9 offences ‘arrestable’, giving the police significant additional powers.

If in doubt over any legal issue relating to slow worms contact the relevant Statutory Nature Conservation Organisation (SNCO) for advice.

This is only an interpretation of the law – reference should always be made to the original texts (UK & European Legislation). 

What to do if you have slow-worms on your land. Advice for landowners – how you can help?

Having slow-worms on your land can be a great benefit. Slow-worms eat many garden pests but are harmless and very unobtrusive themselves. Compost heaps are a favoured habitat for slow-worms as they provide heat and are easy to burrow in. Compost heaps also attract many of the animals such as slugs and snails that slow-worms eat. Care needs to be taken when using or turning the compost so that the slow-worms are not harmed.

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It is ideal to have several compost heaps which are not too efficient as this will provide the best wildlife cover, resulting in a rotation of 2–5 years.

For wildlife, the heap is best left alone for as long as possible, and definitely between November and mid-March, when cold-blooded animals, small mammals and invertebrates may be over-wintering in it. Very gentle turning of open heaps with a fork is best done once or twice a year, in May after slow-worms have mated, and in October after any young have been born.

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Habitats can be improved by providing structural variation to the ground surface. Creating compost heaps, planting hedges with native species, bramble patches or scattered bushes all provide useful habitats. Many forms of wildlife, such as slow-worms, butterflies and birds benefit by gardens not being too ‘tidy’! 

What to do if a slow-worm site is threatened by a development

Ideally, it is best if slow worms and their habitats are protected before planning permission has been given for development of a site. If a known or suspected slow-worm site is threatened by a development, the local planning authority and the local office of the Statutory Nature Conservation Organisation (SNCO) should be informed as far in advance as possible. These organisations will ensure that they are a serious consideration in the planning process.

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For activities that do not require planning permission it is best to contact the landowner before any work is due to start. The local SNCO or Wildlife Trust might be able to assist and provide advice to the landowner regarding conservation of their population of slow-worms.

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If there is evidence that the law has been broken or is about to be, the police should be informed, the best contact being a Police Wildlife Liaison Officer. In England, Natural England can help to clarify the law around slow-worms – you can find the contact for your regional office on their website. 

What to do if slow-worms are discovered during a development

If you are developing a site and slow-worms are only discovered after development has commenced, all works should be halted until a slow-worm survey has been undertaken and appropriate measures taken to protect them on site. Remember it would be an offence to proceed with work which will harm slow-worms. We can organise a survey and undertake mitigation works for you – please contact us.

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For the development to proceed, special protection must be provided for the slow-worms. This is termed mitigation, and specialist licensed ecological consultants such as JPR Environmental provide its strategies. Mitigation normally takes the form of improving or creating habitat within the development site or translocating slow-worms to another suitable site, see below for more details.

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If you are a private individual and are worried about slow-worms on a development site, please contact your regional Natural England office (you will find contact details on their website) or, if there is one, contact the ecologist at your local council. 

Mitigation for slow-worms

Experienced ecological consultants must provide mitigation strategies, as specific requirements need to be met if Local Planning Authorities are to grant permission for a development. JPR Environmental offer a complete service for design, implementation and management of slow-worm mitigation projects.

Typical mitigation measures for slow-worms include exclusion fences, creating hibernacula and translocation.

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In cases where planning permission has been granted to sites that contain slow-worms, they may have to be excluded from certain areas. This can be done by fencing around the area that is known to contain the slow-worms. Ring-fencing contains the slow-worms during the development to protect them from machinery and other operations.

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This method is only appropriate if the site will remain suitable or be enhanced for the slow-worms once development is complete. If the site is not to be suitable then the slow-worms will need to be translocated to another suitable site. This also employs ring-fencing but is only considered as a last resort because translocations are not always successful and the methods are costly in both time and money.

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Structures known as hibernacula can be constructed to greatly improve conditions for slow-worms. Hibernacula provide hibernating habitats giving protection from even the most severe frosts and when scrub vegetation has grown on top of the structure they can also provide foraging and basking habitats.