Anguis fragilisSlow Worm

Geographic Range

The slow worm Anguis fragilis is widely distributed across the western Palearctic region. Its native range includes western and central Europe and the Balkan Peninsula. In addition, isolated populations are believed to occur in Italy and western Scandinavia. It ranges nearly as far north as the Arctic Circle. (Brown and Roberts, 2008; Gvozdik, et al., 2010; Smith, 1990)


The slow worm is semi-fossorial, spending the majority of its time underground. It prefers a damp, cool environment, and its favored habitats include open woodland, grassland, and heath. Preferring to stay out of the open, the slow worm will often hide under stones or other surface debris. It generally spends the winter months in an underground burrow. As a result, the slow worm is difficult to observe in the wild, despite often living in close proximity to humans. (Brown and Roberts, 2008; Hubble and Hurst, 2006; Platenberg and Griffiths, 1999; Smith, 1990)

Physical Description

The slow worm is a smooth, elongate legless lizard, with a snout-vent length (SVL) of between 120-200 mm. Adults are typically gray-brown to copper in color, while juveniles are pale gold or silver with dark sides and ventral coloration. Sexual dimorphism is observed in this species. Females have dark stripes along the back and sides of the body, while males lack stripes. A small percentage of males have distinctive blue spots on the dorsal surface, especially in the eastern part of its range. (Capula and Luiselli, 1993; Capula, et al., 1997; Hubble and Hurst, 2006; Smith, 1990)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range mass
    20 to 100 g
    0.70 to 3.52 oz
  • Range length
    120 to 200 mm
    4.72 to 7.87 in


A young slow worm will develop most rapidly in its first year after birth, growing to an average snout-vent length (SVL) of 100 mm. In subsequent years, it will continue growing at a slower rate until it reaches adult size. (Galan and Ferreiro, 2004; Smith, 1990)


The slow worm is an ovoviviparous species. Eggs develop inside the female, and the young are born live. The breeding season and gestation period of the slow worm vary across its range. In the U.K., the breeding season occurs around April or May, and the young are born in August or September. In the Iberian Peninsula, where the climate is warmer, mating may begin as early as March. (Galan and Ferreiro, 2004; Smith, 1990)

  • Breeding interval
    Female slow worms generally reproduce every other year.
  • Breeding season
  • Range number of offspring
    3 to 20
  • Range gestation period
    3 to 5 months
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female


The slow worm is perhaps the longest-lived species of lizard in the world. The longest recorded lifespan in captivity was 54 years. (Smith, 1990)

  • Range lifespan
    Status: captivity
    54 (high) years
  • Average lifespan
    Status: wild
    30 years


Slow worms hide in subterranean burrows for most of the year, making it difficult to observe their behavior. In the U.K., they spend the colder months from October to March underground, only emerging in April to breed. They may disappear underground again during the hottest part of the summer.

Slow worms are not generally territorial, but agonistic encounters can occur during the breeding season, when males become more aggressive. In wild populations, slow worms of both sexes have been observed with bite scars from conspecific males.

On mild summer days, slow worms can be found at the surface, usually hiding underneath sun-warmed rocks. Gravid females appear to require a higher body temperature and will sometimes emerge to bask in direct sunlight. (Capula and Luiselli, 1993; Galan and Ferreiro, 2004; Gonzalo, et al., 2004; Platenberg and Griffiths, 1999)

Communication and Perception

Slow worms have a well-developed vomeronasal organ and rely largely on olfactory cues to detect prey, identify conspecifics, and avoid predators. Pheromones appear to be an important communication pathway for this species, allowing a slow worm to determine the sex of a conspecific. (Gonzalo, et al., 2004; Toubeau, et al., 1994)

Food Habits

The slow worm is carnivorous, primarily feeding on slugs and earthworms. (Smith, 1990)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms


Predators of the slow worm include snakes and some birds of prey. When threatened by a predator, the slow worm is capable of autotomizing its tail. The tail can be regenerated, but the new tail is not the same color or internal structure as the original. (Bryant and Bellairs, 1967; Smith, 1990)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • snakes
    • birds of prey

Ecosystem Roles

A predator on invertebrates in soil and soil surface. Preyed upon by larger vertebrate predators. (Brown and Roberts, 2008; Smith, 1990)

Economic Importance for Humans: Positive

In the U.K., it is not uncommon to encounter slow worms in suburban gardens. They have a positive impact as they feed on garden pests, particularly slugs. (Smith, 1990)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

These lizards are harmless and have no negative impacts for humans.

Conservation Status

Slow worm populations have declined in the past several decades. A major factor in their disappearance has been habitat disruption due to urban development. In the U.K., the 1981 Wildlife and Countryside Act requires developers to translocate populations before beginning construction. However, the effectiveness of this measure is difficult to evaluate. (Hubble and Hurst, 2006; Platenberg and Griffiths, 1999; Smith, 1990)

Other Comments

The population structure of this wide-ranging anguid lizard has been studied; Gvozdik et al., 2010, found that it is likely a complex of species. (Gvozdik, et al., 2010)


Ayley Shortridge (author), Michigan State University, James Harding (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


Referring to a burrowing life-style or behavior, specialized for digging or burrowing.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.


chemicals released into air or water that are detected by and responded to by other animals of the same species


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


uses sight to communicate


Brown, R., N. Roberts. 2008. Feeding state and selected body temperatures in the slow-worm (Anguis fragilis). Herpetological Journal, 18: 59-62.

Bryant, S., A. Bellairs. 1967. Tail regeneration in the lizards Anguis fragilis and Lacerta dugesii. Journal of the Linnean Society of London, 46: 297-305.

Capula, M., L. Luiselli. 1993. Ecology of an alpine population of the slow worm, Anguis fragilis. Herpetozoa, 6: 57-63.

Capula, M., L. Luiselli, E. Capanna. 1997. The blue‐spotted morph of the slow worm, Anguis fragilis: Colour polymorphism and predation risks. Italian Journal of Zoology, 64/2: 147-153.

Galan, P., R. Ferreiro. 2004. Reproductive ecology of the slow worm (Anguis fragilis) in the northwest Iberian Peninsula. Animal Biology, 54/4: 353-371.

Gonzalo, A., C. Cabido, J. Martin, P. Lopez. 2004. Detection and discrimination of conspecific scents by the anguid slow-worm Anguis fragilis. Journal of Chemical Ecology, 30/8: 1565-1573.

Gvozdik, V., D. Jandzik, P. Lymberakis, D. Jablonski, J. Moravec. 2010. Slow worm, Anguis fragilis (Reptilia: Anguidae) as a species complex: Genetic structure reveals deep divergences. Molecular Phylogenetics and Evolution, 55/2: 460-472.

Hubble, D., D. Hurst. 2006. Population structure and translocation of the slow-worm, Anguis fragilis l.. Herpetological Bulletin, 97: 8-13.

Platenberg, R., R. Griffiths. 1999. Translocation of slow-worms (Anguis fragilis) as a mitigation strategy: a case study from south-east England. Biological Conservation, 90/2: 125-132.

Smith, N. 1990. The ecology of the slow-worm (Anguis fragilis l.) in southern England. Master's thesis: University of Southampton.

Toubeau, G., C. Cotman, V. Bels. 1994. Morphological and kinematic study of the tongue and buccal cavity in the lizard Anguis fragilis (Reptilia: Anguidae). The Anatomical Record, 3: 423-433.