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Common slow worm

The common slow worm (Anguis fragilis) is a legless lizard in the family Anguidae, native to temperate regions of Europe. Genetic studies indicate that populations traditionally classified as A. fragilis may represent a complex of several closely related species.^[1] It is often mistaken for a snake due to its slender, elongated body lacking external limbs, smooth and glossy scales, and overall length of up to 50 cm.^[2]^[3] Adults typically exhibit a uniform gray-brown to coppery coloration, while juveniles display a more metallic gold or silver hue with darker dorsal stripes; females may have prominent dark vertebral lines, and some males feature blue spots on the flanks.^[3]^[2] Unlike true snakes, it possesses movable eyelids, external ear openings, and a notched tongue, and it sheds its skin in irregular patches rather than whole.^[2] This species occupies diverse habitats across its range, favoring damp, vegetated areas such as open woodlands, grasslands, heathlands, meadows, and even urban gardens or allotments where it can find cover under stones, logs, or in self-dug burrows.^[3]^[2] It is semi-fossorial, spending much of its time underground or in crevices to regulate temperature and avoid predators, emerging primarily during mild weather from April to October and hibernating in communal groups during winter.^[3]^[2] The geographic distribution spans western and central Europe, including the British Isles (widespread in England, Wales, and parts of Scotland), Scandinavia, France, Germany, and the Balkan Peninsula, with isolated populations extending to northern Italy and near the Arctic Circle in Scandinavia; it reaches eastward into western Russia and parts of Asia Minor.^[3]^[2] Slow worms are carnivorous, preying mainly on soft-bodied invertebrates like slugs, earthworms, snails, and insects, which they capture using backward-curving teeth for a secure grip on slippery prey; they are most active at dusk or dawn, foraging slowly across the ground.^[3]^[2] Reproduction is ovoviviparous, with mating occurring in spring (April-May in the UK), followed by a gestation of about three to four months, culminating in the birth of 3-12 live young (each around 4 cm long) in late summer (August-September); there is no parental care post-birth, and males may bite females during courtship.^[3]^[2] Individuals can live 20-30 years in the wild, with records up to 54 years in captivity, and they employ defensive strategies like autotomy (tail shedding) and defecation when threatened by predators such as birds, mammals, or domestic cats.^[2] Although classified as Least Concern on the IUCN Red List due to its wide distribution and stable global population, the common slow worm faces localized declines from habitat fragmentation, agricultural intensification, road mortality, and persecution due to misidentification as venomous.^[1]^[3] It is legally protected in several European countries, including the UK under the Wildlife and Countryside Act 1981, where it is listed on Schedule 5 to prevent intentional harm or disturbance.^[2]^[3]

Taxonomy and classification

Nomenclature and synonyms

The binomial name of the common slow worm is Anguis fragilis Linnaeus, 1758. The genus name Anguis derives from the Latin word for "snake," alluding to the species' elongate, limbless body that resembles a serpent. The specific epithet fragilis is Latin for "fragile" or "brittle," referring to the lizard's tail, which readily autotomizes (breaks off) as an antipredator defense.^[1] Linnaeus described the species in his Systema Naturae (10th edition), designating Sweden as the original type locality, later restricted to that region by Mertens and Müller in 1928.^[1] Common names for A. fragilis include slow worm (or slowworm, especially in British English), blindworm, and deaf adder. The term "blindworm" is etymologically unrelated to vision impairment and stems from the Old High German plintslīhho (meaning "shining" or "glistening"), describing the animal's smooth, polished scales; similarly, "deaf adder" arises from historical misconceptions about its sensory abilities and snake-like form.^[1] Historically, A. fragilis has been subject to taxonomic revisions, with former subspecies such as A. f. peloponnesiacus Stepanek, 1937, now synonymized under related species like A. cephallonica. Early classifications often misidentified it as a true snake due to its morphology, contributing to its placement in the genus Anguis alongside colubrid-like taxa in pre-Linnaean works.^[1]^[4]

Relation to Anguis species complex

The genus Anguis has been recognized as a cryptic species complex since the early 2010s, with A. fragilis serving as the nominate species primarily distributed in northern and western Europe. Genetic analyses revealed deep divergences within what was traditionally considered a single widespread species, prompting taxonomic revisions that elevated several lineages to full species status. These revisions highlight the role of Pleistocene refugia in the Balkans and Italian Peninsula in driving speciation through isolation and subsequent range expansions.^[5] A pivotal study published in 2016 in BMC Evolutionary Biology utilized mitochondrial DNA (cyt-b and ND4 genes) and nuclear markers (c-mos and MC1R) to delineate four distinct species within the complex: A. fragilis in northwestern and central Europe, A. colchica in eastern Europe and the Caucasus, A. graeca in the southern Balkans, and A. cephallonica endemic to the Peloponnese and nearby islands. This research demonstrated reciprocal monophyly among these lineages, with divergence times estimated at 5–10 million years ago, supported by subtle morphological differences such as variation in pholidosis and osteology. Subsequent work has recognized a fifth species, A. veronensis, primarily distributed in Italy and parts of the western Balkans. Earlier work in 2010 had laid the groundwork by identifying four major mitochondrial clades using similar genetic approaches, confirming the polytypic nature of the group without reliance on overt external traits.^[6]^[4]^[7] Distributional overlaps occur primarily in secondary contact zones across Europe, where parapatric species meet post-glacially, including in the Balkans between A. fragilis and A. graeca. A 2021 biogeographic analysis mapped these zones, revealing a ~500 km contact area from Montenegro northward, characterized by limited hybridization based on genetic clines and niche partitioning. In the southern Balkans, A. cephallonica and A. graeca exhibit partial sympatry, with ongoing studies exploring admixture levels, showing no evidence of hybridization. These zones underscore the complex's evolutionary dynamics, with A. fragilis expanding from northern refugia into areas of former overlap.^[8] Morphological distinctions among Anguis species are subtle, aiding identification in contact zones alongside genetics. A. fragilis typically features 24–26 mid-body scale rows, a relatively longer tail (when intact), and osteological traits such as a less robust cranial structure compared to A. colchica, which often has 28 or more rows and more pronounced vertebral fusion. These pholidotic and skeletal differences, quantified in phenotypic studies, reflect adaptive divergences but overlap minimally outside hybrid areas, reinforcing the species delimitations from molecular data.^[9]^[10]

Physical description

Body structure and morphology

The common slow worm (Anguis fragilis) possesses an elongated, cylindrical body devoid of external limbs, a key adaptation distinguishing it as a legless lizard within the Anguidae family. Vestigial limb remnants, including reduced girdles and tiny bones, lie hidden beneath the smooth, overlapping scales that cover the trunk, enabling a streamlined form suited to burrowing and navigating dense vegetation. These scales are shiny and uniform, typically arranged in 24 rows around the midbody (22–26 in most individuals of A. fragilis), with transverse rows numbering 125–150 on the trunk and 130–160 on the tail; underlying osteoderms provide additional rigidity without impeding flexibility.^[11]^[12] The head is compact and only subtly set off from the neck, terminating in a blunt snout that facilitates pushing through substrate. Sensory adaptations include a forked tongue for chemoreception, allowing detection of prey and environmental cues via the vomeronasal organ, and movable eyelids—a definitive lizard trait absent in snakes. External ear openings are present but often small and concealed by scales, consistent with anguine lizards.^[13]^[3]^[14] The tail represents a significant portion of the body, typically comprising about 1.1–1.2 times the snout-vent length in undamaged specimens, and serves as a primary defense mechanism through caudal autotomy. When detached, the tail continues to twitch, diverting predators, and can regenerate over time, albeit shorter, blunter, and sometimes with irregular scalation or scarring. This regenerative capacity is supported by specialized caudal vertebrae and musculature.^[3]^[15]^[16] Internally, the skeleton is highly vertebralized, featuring 54–55 presacral vertebrae, one sacral vertebra, and approximately 95–100 caudal vertebrae, yielding a total of around 150–160 vertebrae to accommodate the elongate form. Reduced pectoral and pelvic girdles minimize mass while preserving axial elongation, enabling limbless propulsion via lateral undulation—sinusoidal waves generated by alternating contraction of longitudinal muscles along the body and tail. This locomotion mode proves versatile across substrates, from loose soil to rough surfaces, as evidenced by biomechanical analyses.^[17]^[18]

Size, coloration, and sexual dimorphism

Adult common slow worms typically measure 30–50 cm in total length, with snout-vent lengths (SVL) ranging from 15–25 cm.^[19] Record lengths reach up to 60.7 cm total length, as documented in a specimen from north-western Croatia.^[20] These dimensions reflect a relatively slender, elongated body adapted for burrowing and movement through vegetation. The coloration of common slow worms is generally uniform, featuring shades of brown, grey-brown, or bronze on the dorsal surface, with paler, often cream or yellowish, ventral areas.^[21] Juveniles exhibit distinct dark longitudinal stripes along the back and sides, which fade as they mature, resulting in a more homogenous adult pattern.^[3] Variations include occasional iridescent flecks or spotting, particularly in females.^[22] Sexual dimorphism is pronounced in both size and appearance. Females are typically larger and stouter overall, with more uniform brown coloration and sometimes a dark vertebral stripe or dorsolateral contrast.^[23] Males, in contrast, are slimmer, possess brighter golden or paler flanks, and often have longer tails relative to body size.^[3] This dimorphism extends to head size, with males showing relatively larger heads in some populations.^[24] The slow growth rate of these lizards correlates with extended longevity, with individuals in the wild reaching up to 30 years based on mark-recapture studies.^[3]

Distribution and habitat

Geographic range

The common slow worm (Anguis fragilis) is native to the Western Palearctic, with its core distribution encompassing much of Europe from the Iberian Peninsula, including Portugal and Spain, in the west to the Baltic states and western Russia in the east.^[25] The northern limit reaches southern Scandinavia, including parts of Norway, Sweden, and Finland, while the southern boundary extends to the western Balkans.^[8] This range covers approximately 2,100,000 km², reflecting a broad but discontinuous presence shaped by post-glacial recolonization patterns.^[25] Populations occur in the Channel Islands, such as Guernsey, Jersey, Herm, and Jethou, where the species is considered native.^[26] Genetic analyses indicate these insular groups align closely with nearby continental populations.^[27] A 2021 biogeographic study utilizing mitochondrial and nuclear DNA data has refined the range delineation for A. fragilis, confirming its dominance in northwestern and central Europe while excluding overlap with southern cryptic congeners like A. veronensis in the Italian Peninsula and A. graeca in the eastern Balkans.^[25] This genetic demarcation highlights secondary contact zones, such as along the Baltic coast, where A. fragilis meets A. colchica without extensive hybridization.^[28] Populations at the southern periphery, including suboptimal sites in Catalonia, Spain, exhibit delayed phenology and lower densities, as documented in a 2024 ecological study, underscoring range limits influenced by climatic constraints.^[29] The species occurs from sea level to alpine elevations in the Alps, with records from meadows in the Julian and southeastern Prealps.^[6]

Habitat preferences and microhabitats

The common slow worm (Anguis fragilis) primarily inhabits open, temperate landscapes across its range, favoring environments that provide ample cover and moderate moisture levels. Preferred habitats include open woodlands, grasslands, heathlands, and anthropogenic areas such as gardens and allotments, where vegetation offers shelter without excessive density.^[3]^[2] These sites support the species' semifossorial lifestyle, allowing it to exploit sunny, vegetated patches for basking while avoiding exposure. In contrast, dense forests are generally avoided due to limited sunlight penetration and cooler, shadier conditions that hinder effective thermoregulation.^[29] Within these habitats, slow worms exhibit strong microhabitat preferences centered on refugia that facilitate temperature regulation and protection from predators. Individuals frequently burrow under stones, logs, leaf litter, or artificial debris like compost heaps and rubble piles, using these sites to maintain optimal body temperatures during the active season.^[3]^[2] Substrate selection emphasizes moist, vegetated soils that retain humidity and support invertebrate prey, while arid or overly compacted grounds are shunned to prevent desiccation. During winter, slow worms enter hibernation from October or November through March, often in communal underground dens beneath deep leaf litter, roots, or mammal burrows, sometimes sharing sites with other reptiles or amphibians for thermal efficiency.^[19]^[30] The species thrives in temperate climates with mild winters, where annual temperatures allow reliable emergence in spring. At the southern edges of its distribution, such as in Catalonia, Spain, populations are confined to humid or montane microhabitats, reflecting vulnerability to drought and warmer conditions that exceed thermal tolerances.^[29] A 2024 study of a population near this range limit highlighted suboptimal site occupancy, with lower densities and activity linked to reduced moisture availability during dry periods.^[29]

Behavior and ecology

Diet and foraging strategies

The common slow worm (Anguis fragilis) is primarily carnivorous, with its diet dominated by soft-bodied invertebrates such as slugs, snails, earthworms, insects (including larvae), spiders, and millipedes.^[31]^[32] Although invertebrates form the bulk of its prey, occasional consumption of small vertebrates, such as amphibians and nestling birds, has been recorded in some populations.^[31] Juveniles typically select smaller prey items, reflecting their limited size and gape, while adults show less restriction on prey dimensions.^[32] Foraging in A. fragilis involves active foraging with a sit-and-wait approach, where individuals move slowly through concealed positions, using their notched tongue to perform chemosensory flicks that detect chemical cues from potential prey.^[3]^[2] Once located, prey is seized with the aid of recurved teeth and swallowed whole, facilitated by the lizard's flexible jaws and lack of limbs.^[33] This method suits the slow worm's cryptic lifestyle in leaf litter or under vegetation, where it waits for or slowly approaches mobile or burrowing invertebrates. Dietary composition exhibits seasonal shifts, with gastropods (slugs and snails) comprising a greater proportion during wetter periods due to increased activity of these prey, while earthworms dominate in drier months.^[31] These variations align with environmental moisture levels influencing prey availability across European habitats. By targeting pest species like slugs, A. fragilis serves a beneficial trophic role in gardens and agricultural areas, helping to regulate invertebrate populations without chemical intervention.^[34]

Activity patterns and thermoregulation

The common slow worm (Anguis fragilis) is primarily crepuscular, most active at dawn and dusk for foraging, though it may exhibit diurnal basking in the morning under cover objects such as rocks or logs to raise its body temperature, particularly in spring and summer.^[35] In hotter conditions, individuals may shift to more nocturnal activity to avoid excessive heat.^[36] This pattern integrates with foraging, as activity peaks align with periods of prey availability under similar thermal conditions.^[37] Seasonally, slow worms emerge from hibernation between late March and May, with males typically appearing earlier than females, and remain active until October when they enter hibernation, spanning roughly October to March.^[25] Peak activity occurs from May onward in northern populations, but recent phenological data from southern edges, such as in Catalonia, Spain, indicate a later peak in June-July, reflecting warmer regional climates.^[29] As an ectotherm, the slow worm relies on behavioral thermoregulation, basking in sunny or partially shaded spots to achieve preferred body temperatures of 25-30°C, which support optimal physiological functions like digestion and locomotion.^[38] Field body temperatures average 22.1°C in sunny conditions and 14.7°C when overcast, significantly higher than shaded operative temperatures but below full sun exposure, indicating precise selection of microhabitats for heating while using burrows or shade for cooling during overheating risks.^[35] Slow worms exhibit low-energy movement, characterized by deliberate, undulating locomotion that earns them their name, with limited daily displacements rarely exceeding a few meters.^[39] Home ranges are relatively small, typically spanning 100-500 m², allowing individuals to maintain thermal stability within familiar, resource-rich areas without extensive travel.^[40]

Reproduction and life history

Mating behavior and reproduction

The common slow worm (Anguis fragilis) exhibits mating behavior primarily in spring, shortly after emerging from hibernation, with males becoming territorial and engaging in combat to secure access to receptive females.^[41] Males wrestle rivals in ritualized displays, often entwining their bodies and biting, which can result in visible scars on up to 41% of individuals during the mating period from mid-April to mid-June.^[42] Larger males typically prevail in these contests, reflecting sexual selection pressures linked to subtle dimorphism such as broader heads in males.^[41] Copulation follows successful courtship and can last several hours, with the male biting the female's head or neck to hold her as they entwine; females are generally receptive in the post-hibernation period of March to May.^[3]^[2] Reproduction in A. fragilis is ovoviviparous, with embryos developing internally within the female for a gestation period of 8 to 12 weeks.^[13] Females give birth to live young in late summer, typically from mid-August to mid-September, producing litters ranging from 3 to 20 offspring, with an average clutch size of 6 to 8.^[41]^[3] Breeding occurs biennially in most populations, allowing females to recover resources between reproductive cycles.^[43] There is no parental care following birth; neonates emerge fully formed and independent, dispersing immediately to forage on their own.^[3]^[44]

Growth, longevity, and population dynamics

The common slow worm (Anguis fragilis) exhibits slow growth characteristic of reptiles with low metabolic rates, beginning with neonates measuring 7–10 cm in total length at birth.^[45] Growth proceeds gradually, with individuals reaching sexual maturity at 3–5 years of age and approximately 15–20 cm in length, reflecting their ectothermic physiology and limited energy allocation to somatic development.^[46] This protracted developmental phase contributes to their overall life history strategy, emphasizing survival over rapid reproduction. Longevity in A. fragilis is notable among lizards, with wild individuals typically surviving 20–30 years due to low adult mortality rates, while captive specimens have exceeded 50 years, including a record of 54 years.^[2] Annual adult survival estimates around 0.76 underscore their resilience once mature, allowing populations to persist despite infrequent breeding.^[29] Population dynamics feature densities of 50–200 individuals per hectare in optimal habitats, though lower values (e.g., ~124 individuals/ha) occur at range edges like southern Catalonia.^[29] Age structures are skewed toward adults, comprising over 70% of captured individuals in studied populations, attributable to high juvenile mortality primarily from predation.^[29] A 2024 demographic study at a southern distribution edge revealed stable but slow-reproducing populations, with immature density at 16 individuals/ha and a sex ratio favoring females (0.44 males:females overall).^[29] These patterns highlight vulnerability in early life stages, balancing the species' extended lifespan and low reproductive output.

Predators and threats

Natural predators

The common slow worm (Anguis fragilis) is preyed upon by diverse avian, mammalian, and reptilian species across its range in Europe, with predation pressure varying by habitat and life stage. Juveniles, being smaller and less experienced, face heightened vulnerability to attacks compared to adults, often resulting in higher mortality rates during early development.^[3] Avian predators primarily consist of birds of prey such as kestrels (Falco tinnunculus), buzzards (Buteo buteo), kites, and tawny owls (Strix aluco), which opportunistically hunt slow worms in open grasslands and woodlands. Corvids, including magpies (Pica pica) and crows, also target them, particularly in disturbed or garden settings, while occasional predation by herons has been noted in wetland-adjacent areas.^[46]^[2] Mammalian predators include hedgehogs (Erinaceus europaeus), badgers (Meles meles), and foxes (Vulpes vulpes), which forage for slow worms in soil and under vegetation during nocturnal or crepuscular activity. Domestic cats (Felis catus) pose a significant threat in suburban and garden environments, where slow worms seek cover in compost heaps and leaf litter.^[2]^[47]^[46] Reptilian predators are dominated by larger snakes, such as grass snakes (Natrix helvetica) and adders (Vipera berus), which consume slow worms whole after ambushing them in dense cover; smooth snakes (Coronella austriaca) have also been documented preying on them in specific locales.^[2]^[48] A primary defense against these predators is caudal autotomy, where the slow worm detaches its fragile tail—often longer than the body—to distract and escape attackers; this mechanism, linked to specialized tail morphology, allows survival but incurs costs like reduced mobility and energy for regeneration. Evidence of past autotomy is common, with studies reporting 40-65% of adults bearing non-intact tails or scars, depending on the population, underscoring the prevalence of predation attempts throughout their lifespan.^[3]^[48]^[29]

Human-induced threats

The primary human-induced threat to the common slow worm (Anguis fragilis) is habitat loss and fragmentation, particularly in the UK where urbanization and agricultural intensification have significantly reduced suitable grasslands and open habitats. Development projects often target brownfield sites and rural areas frequented by slow worms, leading to the destruction of refugia such as compost heaps, log piles, and tussocky vegetation essential for shelter and foraging. Intensive farming practices, including overgrazing, frequent mowing, and afforestation, further degrade these microhabitats by eliminating cover and prey availability. Additional threats include habitat fires and re-afforestation of clearings, which reduce suitable open habitats, as noted in recent assessments (as of 2025).^[49]^[50]^[51]^[52] Road mortality poses another significant risk, especially during dispersal periods when slow worms cross rural roads to find mates or new territories, resulting in high vehicle collisions on secondary routes near grasslands. Their secretive, ground-dwelling nature offers some protection, but increased traffic volumes exacerbate this threat in fragmented landscapes.^[53]^[54] Direct persecution occurs when slow worms are misidentified as venomous snakes and deliberately killed, a practice historically linked to fear and lack of awareness, though less common today. Additionally, the widespread use of pesticides and slug pellets in gardens and agriculture reduces populations of invertebrate prey such as slugs, snails, and earthworms, indirectly starving slow worms and disrupting their food chain.^[55]^[56]^[57]^[58] Climate change compounds these pressures by altering thermal regimes, potentially causing range contractions at southern edges through warmer temperatures that exceed optimal thermoregulation thresholds for this ectotherm. Recent modeling indicates that without dispersal, UK reptile populations, including slow worms, face habitat unsuitability in current ranges due to shifting isotherms.^[59]

Conservation and protection

Legal status and protections

The common slow worm (Anguis fragilis) is classified as Least Concern on the IUCN Red List at the global level, based on a 2009 assessment that notes its wide distribution and stable populations across much of its range, though local declines occur in fragmented habitats.^[60] The 2013 European Red List of Reptiles also assesses it as Least Concern, while local populations in the UK show declines linked to habitat loss. In the United Kingdom, the species receives protection under Schedule 5 of the Wildlife and Countryside Act 1981, which prohibits intentional killing, injury, or taking of the animal, as well as intentional disturbance while it occupies a place of shelter or protection, or sale and advertisement for sale; it is also listed as a Species of Principal Importance in England under Section 41 of the Natural Environment and Rural Communities (NERC) Act 2006.^[61]^[49] In Ireland, A. fragilis—considered an introduced species—is protected under the Wildlife Acts 1976 and 2000, with specific guidelines established for translocation of individuals during development projects to mitigate impacts on known populations.^[62]

Conservation challenges and efforts

Population trends for the common slow worm (Anguis fragilis) remain stable in core parts of its range across western and central Europe, but significant declines have been observed in fragmented habitats, particularly those affected by urban development and vegetation changes.^[3]^[63] Long-term monitoring in local UK populations has linked these declines to habitat alterations, with slow-worm numbers decreasing notably in areas undergoing intensive land use changes.^[63] In southern England, historical data indicate population reductions during the late 20th century, exacerbated by brownfield site redevelopment.^[39] Key conservation challenges include the low efficacy of translocation efforts and genetic isolation in urbanized landscapes. A 1999 case study in southeast England translocated slow-worms to mitigate development impacts, but follow-up monitoring revealed poor long-term survival and establishment, with many individuals failing to persist beyond initial relocation.^[64] Subsequent analyses across UK sites confirmed that translocation rarely compensates for population losses, often resulting in high post-release mortality due to inadequate habitat matching and stress.^[65] Additionally, habitat fragmentation in urban areas promotes genetic isolation, as evidenced by structured populations in a 16 km² Swiss study area where gene flow was limited by barriers like roads and built environments.^[66] Active conservation efforts focus on habitat creation and community involvement to bolster populations. In the UK, the Amphibian and Reptile Groups (ARG UK) promote targeted habitat management, including the construction of refugia such as brash piles, log heaps, and vegetated banks in reserves and green spaces to provide shelter and foraging opportunities for slow-worms.^[67] Citizen science initiatives, coordinated by ARG UK, collect distribution records through public surveys, aiding in population monitoring and identifying priority sites for intervention. Recent 2025 research on the contact zone between A. fragilis and A. colchica in eastern Europe highlights the need for enhanced protections in Balkan regions to preserve genetic diversity amid overlapping ranges.^[68] Looking ahead, climate adaptation strategies are essential for southern populations vulnerable to warming temperatures and shifting precipitation patterns. Ensemble modeling predicts range edge contractions for forest-dependent reptiles like the slow-worm, emphasizing the development of resilient habitats with shaded, moist refuges to support thermoregulation under future scenarios.^[69] In the UK, projections indicate stable core ranges but risks to peripheral sites, underscoring the importance of integrated planning to mitigate drought effects on activity and reproduction.^[70]

Evolutionary history

Phylogenetic relationships

The common slow worm, Anguis fragilis, is classified within the family Anguidae, a group of lizards known for diverse body forms ranging from limbed to limbless. Specifically, it belongs to the subfamily Anguinae, which includes other legless "glass lizards" such as genera Ophisaurus and Pseudopus, and is characterized by an elongated, serpentine body adapted for semifossorial lifestyles.^[71] Within Anguidae, the Anguinae forms a monophyletic sister group to the Gerrhonotinae, the subfamily comprising limbed anguids native primarily to the Americas, as resolved by both morphological and molecular phylogenies.^[72] Phylogenetic analyses of the genus Anguis using mitochondrial and nuclear DNA markers, including recent phylogenomic studies, place A. fragilis within a species complex that diverged from the basal species A. cephallonica around 12 million years ago in the Miocene. A. fragilis represents the western lineage of this complex, separating from eastern and southern European congeners like A. colchica and A. graeca approximately 3–4 million years ago, with diversification of the complex beginning around 7 million years ago.^[73]^[74] Genetic distances between A. fragilis and its closest relatives range from 7% to 9% in mitochondrial genes, underscoring deep evolutionary divergence. Phylogenetic relationships have been further clarified by 2023 analyses using whole-genome data, supporting the monophyly of the A. fragilis complex and revealing mitonuclear discordance due to ancient hybridization events.^[74] A notable aspect of Anguis phylogeny is the occurrence of rare hybridization in parapatric contact zones, particularly between A. fragilis and A. colchica in Central Europe, where admixed individuals show intermediate morphology and genetics but limited gene flow due to partial reproductive barriers.^[75] Within Anguidae more broadly, the limbless condition observed in A. fragilis and other Anguinae represents a convergent evolutionary trait, having arisen independently at least three times across the family, driven by selection for burrowing adaptations in disparate lineages.^[76]

Biogeography and historical distribution

The common slow worm (Anguis fragilis) endured the Pleistocene ice ages primarily in refugia within the Iberian and Balkan (particularly Dinaric) peninsulas, where milder climatic conditions allowed survival amid widespread glaciations across Europe.^[73] These refugia facilitated genetic divergence among isolated populations, shaped by repeated cycles of isolation during glacial maxima and limited connectivity during interglacials.^[77] Following the Last Glacial Maximum approximately 20,000 years ago, retreating ice sheets enabled post-glacial recolonization, with populations expanding northward into central and northern Europe around 10,000–12,000 years before present as forests and suitable habitats advanced.^[78] Phylogeographic studies indicate a single dominant haplogroup across much of its range, suggesting colonization primarily from a northern extra-Mediterranean refugium in the Dinarides, with evidence for at least three sub-refugia within the southern Balkans. Biogeographic patterns of A. fragilis reveal evidence of vicariance in the Balkans, where topographic complexity and historical barriers promoted lineage splitting and secondary contact zones among lineages.^[25] A 2021 study synthesizing genetic and distributional data across the Western Palearctic highlighted how these processes contributed to parapatric distributions, with Balkan populations exhibiting distinct phylogeographic breaks linked to Pleistocene fragmentation events.^[25] At least three major refugia in the southern Balkans are inferred for A. fragilis, underscoring the region's role as a hotspot for intraspecific diversification.^[77] Genetic diversity in A. fragilis is notably higher in southern refugia, particularly in rugged Balkan terrains, where multiple haplotypes reflect long-term persistence and limited gene flow during glaciations.^[6] In contrast, northern colonized areas display reduced variation, characterized by a single dominant haplogroup and lower intraspecific p-distances (≤1.1%), indicative of founder effects and rapid post-glacial dispersal from fewer source populations.^[78] Overall, the species exhibits relatively low genetic variation compared to congeners, with 34 mitochondrial haplotypes identified across its range, emphasizing the legacy of Pleistocene dynamics on contemporary patterns.^[6] In recent millennia, A. fragilis has maintained range stability partly through human-modified landscapes that provide suitable edge habitats, though ongoing climate warming poses risks of future distributional shifts northward or to higher elevations.^[59] Potential alterations include expanded activity periods and reproductive output in warmer conditions, but increased habitat fragmentation and extreme weather could counteract these benefits.^[59]

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Skin structure of the slow worm lizard Anguis fragilis (Anguidae ...
Mar 2, 2024 · The structure of the skin and superficial micro‐ornamentation in the slow worm Anguis fragilis, a limbless lizard with a fossorial activity, was examined
[14]
Vertebral Comparative Anatomy and Morphological Differences in ...
Oct 5, 2018 · Anguis fragilis DE 14-21, 24, 25, 45-48, 102a, 103a. Ophisaurus ... As mentioned, the number of vertebrae in the presacral region is usually 55.
[15]
Tests on Locomotion of the Elongate and Limbless Lizard Anguis ...
Anguis fragilis were filmed while traversing plane surfaces, fields of nails and pins at different spacings, and channels of different diameter.Missing: scale count ratio
[16]
[PDF] Slow Worm Anguis fragilis - ARG UK
Size – Much smaller than grass snakes, adults can reach up to 30-45cm, with newly born slow worms measuring just 7-. 10cm. Features – Slow worms have a ...
[17]
two record-breaking specimens of Anguis fragilis from north-western ...
fragilis attains the longest total length, 509 mm, in our dataset, while a male of A. colchica is the individual with the longest SVL -261 mm, see Tables 2, S2) ...
[18]
[PDF] Blue colour of the ventral body part of Eastern Slow Worm Anguis ...
Nov 13, 2010 · Typical coloration of Anguis fragilis s.l. is brown, bronze, chocolate, grayish or yellowish and coloration of the ventral body parts tends ...
[19]
Slowworm - Anguis fragilis - NatureSpot
Females are brown or copper coloured on the back, with brown or black sides, often with lighter iridescent flecks, and sometimes with a dark stripe passing ...
[20]
Slow worm - Anguis fragilis | The World of Animals
Feb 27, 2016 · A single dorsal stripe running from about the nape of the neck to the tail is present in some, but not all, animals. Some animals possess a ...<|control11|><|separator|>
[21]
[PDF] SEXUAL SIZE DIMORPHISM IN EASTERN SLOW-WORM (Anguis ...
Anguis fragilis colchica samples from Rupea, Romania (first column males, second column females). Page 5. jaws power in A. f. colchica is increased by the ...
[22]
(PDF) The distribution and biogeography of slow worms (Anguis ...
The slow worm (Anguis fragilis) is a lizard with a wide distribution throughout Europe Jablonski et al. 2021). The genus Anguis comprises five species: Anguis ...
[23]
Slow worm - Overview | Better Planet Education
Anguis fragilis. IUCN Status: Near Threatened. Population Trend: decreasing. Distribution: Found throughout UK, including Jersey, Guernsey, Herm and Jethou in ...Explore Related Resources · Britain's Disappearing... · Animal Rights
[24]
Anguis fragilis LINNAEUS, 1758 - The Reptile Database
Slow worm, Anguis fragilis (Reptilia: Anguidae) as a species complex: Genetic structure reveals deep divergences. Molecular Phylogenetics and Evolution 55 ...Missing: osteological traits
[25]
[PDF] Two species of slow worm (Anguis fragilis, A. colchica) present in ...
Their contact zone runs from the north-eastern. Balkans, through Pannonia to northern Central Europe. In northern Poland, the contact zone has been located ...
[26]
Phenological, ecological, and demographic data of the slow worm ...
Aug 29, 2024 · The slow worm (Anguis fragilis) is a lizard with a wide distribution throughout Europe ( Strzała et al. 2017 ; Jablonski et al. 2021 ). The ...Missing: taxonomy | Show results with:taxonomy
[27]
https://reptile-database.reptarium.cz/species?genus=anguis&species=fragilis
[28]
A method of obtaining dietary data for slow worms (Anguis fragilis ...
The food contents of Anguis fragilis, included in the same family, are composed of mollusks, earthworms, millipedes, amphibians, insects and their larvae ( ...
[29]
[PDF] The diet of the Slow Worm, Anguis f. fragilis LINNAEUS, 1758, in the ...
All specimens utilized come from sites close to the edges of Swiss Mountain. Pinewoods (Pinus mugo), at about 700 -. 1200 m altitude. Slow Worms were collected ...Missing: altitudinal | Show results with:altitudinal
[30]
[PDF] A case of cannibalism behavior of the Slow worm, Anguis fragilis ...
Mar 13, 2011 · Adaptation of ambush foraging may induce loss of chemical discrimination of the prey (Cooper & van Wyk,. 1994). Since the lizards are kept in ...Missing: strategy | Show results with:strategy
[31]
Nature in June - New Forest Local Group
Jun 1, 2025 · The slow worm is an unhurried creature, and it feeds on slow-moving prey such as worms and slugs. The fact that it is slow itself means that ...
[32]
Null models and the thermal biology of the anguid lizard Anguis fragilis
Microclimatic changes associated with dense canopies in native forests or tree plantations could affect squamate assemblages. In this study, we tested the ...
[33]
https://biozoojournals.ro/bihbiol/cont/v5n1/bb.111201.Cicek.pdf
[34]
[PDF] Feeding state and selected body temperatures in the slow-worm (<i ...
This paper tests for a postprandial thermophilic response in a cool habitat species that shows low field activity temperatures. The European lizard, Anguis ...Missing: dense | Show results with:dense
[35]
Feeding state and selected body temperatures in the slow-worm ...
Aug 6, 2025 · Here it was examined in an anguid lizard, namely the slow-worm Anguis fragilis, which is a semi-fossorial cool temperate species that exhibits ...
[36]
[PDF] Population structure and translocation of the Slow-worm, Anguis ...
unfavourable habitat. As Slow-worms have a small home range averaging approximately 200m2 with few moving more than 4m in a single day. (Smith, 1990) ...Missing: locomotion | Show results with:locomotion
[37]
Spatial capture–recapture analysis of artificial cover board survey ...
Sep 13, 2017 · We use data from a spatial capture–recapture study on the slow-worm Anguis fragilis where ACOs were used to capture these habitat generalist ...Missing: lifespan wild
[38]
sexual combats, matings, and reproductive phenology in an alpine ...
Jan 11, 2016 · Mating occurs between April and May, while parturition takes place from mid-August to mid-September.
[39]
(PDF) Reproductive ecology of the slow worm (Anguis fragilis) in the ...
Aug 7, 2025 · The reproductive characteristics of the slow worm (Anguis fragilis) were studied in A Coruña (Galicia, NW Spain) in 1999, 2000, 2001 and 2002.Missing: rows | Show results with:rows
[40]
[PDF] Biennial reproduction and clutch parameters in an alpine population ...
Clutch size ranged from 6 to 13 and the constancy of the ratio of clutch size and female snout-vent length was statistically highly significant.Missing: gestation | Show results with:gestation
[41]
(PDF) Parental Behavior in Anguid Lizards - Academia.edu
... parental behavior is perhaps absent in viviparous Anguis fragilis and Ophiodes. Meager circumstantial evidence suggests that chemical cues influence those ...<|control11|><|separator|>
[42]
Slow worm facts - Trees for Life
A newborn slow worm is 7-10 cm in length, and growth is relatively slow, with it taking 6-8 years for an individual to reach its full size. Males reach ...
[43]
European slowworm | Wildlife Online
Colour/Appearance: Typically brown-grey in colour with a copper lustre on back. Males tend to be more uniform in colour than females, which often present with ...Missing: coloration | Show results with:coloration
[44]
Slow worm | NatureScot
Mar 7, 2025 · Their natural predators include birds of prey and larger mammals like badgers and foxes.
[45]
[PDF] Two observations concerning slow worm Anguis fragilis antipredator ...
Although a wide range of animals may occasionally prey upon slow worms, the major predator groups on slow worms are likely birds and reptiles. (Martín & López, ...
[46]
[PDF] Slow-worm - Worcestershire County Council
Most rural records tend to come from nature reserves. 3. Current factors affecting the species. • Loss of habitat due to intensive agricultural land use and ...
[47]
Slow-worm SAP – Nottinghamshire Biodiversity Action Group
Lack of habitat management, with a loss of open areas due to scrub encroachment. Over-tidying, mowing and strimming, and overgrazing which reduce available ...
[48]
Slow Worm (Anguis fragilis) - British Reptiles - Woodland Trust
Like much of the UK's wildlife, they are threatened by habitat loss. Trees woods and wildlife. Adder. The adder is the UK's only venomous snake, but it's ...
[49]
Species Focus: Slow Worm - Ealing Wildlife Group
Jun 25, 2023 · Like other reptiles, they hibernate, spending the winter from October onwards hibernating under piles of leaves, burrowed underground or within ...
[50]
Amphibian and Reptile Road Mortality in Special Nature Reserve ...
Feb 23, 2022 · Individuals of A. fragilis had a low road mortality rate, perhaps because of its secretive lifestyle, although Wells and colleagues [65] have ...
[51]
but don't be fooled. This is no snake... | Countryfile.com
Oct 10, 2025 · The oldest specimen recorded in captivity lived for at least 54 years, so an adult in the wild may be more than 25 years of age.
[52]
The Slow Worm (Anguis fragilis) - Flora and Fauna of the UK
Nov 18, 2024 · This page provides an overview of the slow worm's physical characteristics, behaviour, habitat, diet, reproduction, and the conservation status ...The Slow Worm (anguis... · Habitat And Distribution · Diet And Behaviour
[53]
What to Do if You Find a Slow Worm in Your Garden - Yahoo Life UK
Aug 15, 2025 · The greatest threat is humans: habitat loss due to intensive agriculture, the use of pesticides and slug pellets, and careless killing out of ...
[54]
Slow-worms – the gardener's best friend
Jul 25, 2022 · Their presence can be an important indicator of a balanced eco-system not adversely impacted by pesticides and predation by non-native species ...
[55]
The effect of the climate crisis on UK reptile populations - Froglife
Feb 22, 2021 · Zero dispersal resulted in population contractions for all UK species, indicating climate change driven population collapse. This demonstrates ...
[56]
[PDF] European Red List of Reptiles - IUCN Portals
Order. Family. Species. IUCN Red. List Category. (Europe). IUCN Red. List Criteria ... Anguis fragilis. LC. LC. SQUAMATA. ANGUIDAE. Pseudopus apodus. LC. LC.
[57]
Wildlife and Countryside Act 1981, SCHEDULE 5 - Legislation.gov.uk
Changes to legislation: Wildlife and Countryside Act 1981, SCHEDULE 5 is up to date with all changes known to be in force on or before 30 October 2025.
[58]
[PDF] Ireland Red List No. 5: Amphibians, Reptiles & Freshwater Fish
documents that were referred to for this assessment (IUCN, 2001; 2003; 2010a) and the ... (2000) The present status of the slow-worm, Anguis fragilis L., in ...
[59]
Evaluating survey design and long-term population trends in slow ...
May 20, 2025 · Long-term population monitoring suggested that vegetation change is a major factor contributing to declines in slow-worm numbers within a local ...
[60]
Translocation of slow-worms (Anguis fragilis) as a mitigation strategy
At the receptor site, which had no previous slow-worm population, recaptures of translocated slow-worms declined during 2 years of subsequent monitoring; ...Missing: lifespan mark-
[61]
[PDF] Effectiveness of translocation in mitigating reptile-development ...
To determine the effect of translocation, we investigated six sites within the UK that had received populations of translocated slow-worm Anguis fragilis, ...Missing: efficacy | Show results with:efficacy
[62]
[PDF] Effect of habitat fragmentation on the genetic structure of slow-worm ...
To perform further population genetics analysis between 8 and 15 suitable microsatellites for Anguis fragilis were needed since no published microsatellites are ...
[63]
[PDF] Reptile Habitat Management Handbook | ARG UK
On coastal sand dunes, this species favours frontal dune ridges, preferring areas of dense marram grass combined with abundant exposed sand and a south or ...<|control11|><|separator|>
[64]
Contact zone of slow worms Anguis fragilis Linnaeus, 1758 and ...
Jan 6, 2025 · Background Legless lizards, the slow worms of the genus Anguis, are forming secondary contact zones within their Europe-wide distribution.
[65]
Ensemble modelling for smart conservation strategies for forest ...
In the context of climate change, many species face additional challenges such as habitat destruction due to anthropogenic impacts, including fragmentation and ...
[66]
(PDF) Climate change modelling of English amphibians and reptiles
Climate change poses a significant threat to many British reptile and amphibian species. Only four of the thirteen species are projected to have stable ranges ...
[67]
Phylogenetic relationships and divergence dating in the Glass ...
The Glass Lizards are a subfamily (Anguinae) of Anguid Lizards with an elongated limbless body plan that occur throughout the Northern Hemisphere.
[68]
The Phylogenetic Relationships of Major Lizard Families Using ...
Lizards with limbs and those without exhibit distinct locomotor abilities when adapting to their habitats, which in turn necessitate varying degrees of energy ...
[69]
An ancient lineage of slow worms, genus Anguis (Squamata
Slow worms, legless lizards of the genus Anguis Linnaeus, 1758, inhabit a large territory of the Western Palearctic region including all three southern European ...Missing: etymology | Show results with:etymology
[70]
Distribution and hybridization of Anguis fragilis and A. colchica in ...
Aug 5, 2025 · Based on pronounced divergences in molecular markers the subspecies of the slow worm, Anguis fragilis, have been recently elevated to species ...
[71]
a phylogenetic analysis of body-form evolution in anguid lizards
Within anguines, Anguis fragilis has evolved a relatively elongate trunk, relatively short tail, and smaller overall body size (relative to other anguines), and ...
[72]
Contrasting evolutionary histories of the legless lizards slow worms ...
May 10, 2016 · Four Anguis species with mostly parapatric distributions occur in the Balkan Peninsula. They show different levels of genetic diversity.
[73]
Phylogeography and postglacial colonization of Central Europe by ...
Nov 27, 2017 · Anguis fragilis is represented by a single haplogroup, while A. colchica by three haplogroups. This suggests four independent sources/refugia ...