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Acrochordus
Acrochordus
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Acrochordus
Temporal range: 11.608–0 Ma Middle Miocene - present [1]
Acrochordus arafurae
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Superfamily: Acrochordoidea
Family: Acrochordidae
Bonaparte, 1831
Genus: Acrochordus
Hornstedt, 1787
Synonyms[2]

Acrochordidae:

List
    • Acrochordina Bonaparte, 1831
    • Acrochordidae Bonaparte, 1840
    • Acrochorniens A.M.C. Duméril, 1853
    • Acrochordidae Jan, 1863
    • Acrochordinae Boulenger, 1893
    • Acrochordoidae McDowell, 1975
    • Acrochordini Dowling & Duellman, 1978

Acrochordus:

List
    • Acrochordus Hornstedt, 1787
    • Chersydrus Cuvier, 1817
    • Chersidrus Oken, 1817
    • Acrochordus Gray, 1825
    • Chersydreas Gray, 1825
    • Chershydrus Bonaparte, 1831
    • Verrucator Schlegel, 1837
    • Chersydraeas Gray, 1849
    • Potamophis Schmidt, 1852
    • Chersydraeus Duméril, Bibron & Duméril, 1854
    • Acrochordus Boulenger, 1893

The Acrochordidae, commonly known as wart snakes,[3] Java wart snakes,[4] file snakes, elephant trunk snakes, or dogface snakes are a monogeneric family of snakes.[3] The sole genus Acrochordus are basal aquatic snakes found in Australia and tropical Asia, with three species recognized.[4]

Description

[edit]
Head of Acrochordus arafurae

All are entirely aquatic, lacking the broad belly-scales found in most other snakes and possessing dorsally located eyes. Their most notable feature is their skin and scales. The skin is loose and baggy, giving the impression of being several sizes too large for the snake, and the scales, rather than overlapping, possess tiny pyramidal projections that led to their common names. Adults grow to between 60 and 243 centimetres (24 and 96 in) in length.

This type of snake are ambush predators, lurking at the bottom of rivers, streams and estuaries, and waiting for fish to approach, which they grip with their coils. The rough scales allow them to hold the fish despite the mucus coating.

Geographic range

[edit]

Found from western India and Sri Lanka through tropical Southeast Asia to the Philippines, south through the Indonesian island group to Timor, east through New Guinea to the northern coast of Australia to Mussau Island, the Bismarck Archipelago and Guadalcanal Island in the Solomon Islands.[2]

Relation to humans

[edit]

These animals are rapidly becoming rare as their hides are used for handbags and leather (stripped of scales, of course). Numerous attempts have been made by both zoos and private reptile collectors to keep them, but in all cases, they have been reluctant to feed and prone to skin infections.

Species

[edit]
Common name Scientific name IUCN Red List Status Distribution Picture
Arafura file snake[5] Acrochordus arafurae
McDowell, 1979
LC IUCN[6] New Guinea and northern Australia.
Little wart snake[7] Acrochordus granulatus
(Schneider, 1799)
LC IUCN[8] Peninsular India, Sri Lanka, Myanmar, the Andaman Islands, Thailand, Cambodia, Vietnam, China, the Philippines, Malaysia, Papua New Guinea, the Solomon Islands, and coastal northern Australia.
Elephant trunk snake[9] Acrochordus javanicus
Hornstedt, 1787
LC IUCN[10] Southeast Asia from Vietnam, Cambodia and Thailand, south through Malaysia, Singapore and Indonesia (Sumatra, Java and Borneo).

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
Acrochordus (file snakes) is a of non-venomous, fully aquatic snakes in the family Acrochordidae, comprising three extant (A. arafurae, A. granulatus, and A. javanicus) that inhabit freshwater, brackish, and coastal marine environments from through to and . These primitive colubroid snakes are distinguished by their baggy, wrinkled skin, small granular scales with a rough, file-like texture, and dorsoventrally flattened tails adapted for swimming, with no specialized fangs or glands. All are ovoviviparous, piscivorous predators with low metabolic rates and large blood volumes that enable prolonged submersion, though they are clumsy and nearly helpless on land. The genus represents the sole modern lineage of Acrochordidae, a family basal to advanced colubroids (Colubroidea), with fossil relatives dating back to the Paleogene; extant species diverged during the Miocene around 16–20 million years ago. A. javanicus (Javan file snake) is the largest, reaching over 2 meters and more than 10 kg, primarily in rivers and swamps of Indonesia and Southeast Asia, where it faces pressure from skin harvesting. A. arafurae (Arafura file snake), up to 2.5 meters, occupies billabongs and floodplains in northern Australia and southern New Guinea, reproducing infrequently (every 8–10 years) with litters of 6–27 young. The smallest, A. granulatus (little file snake), grows to about 1 meter and tolerates a wide salinity range from India to the Solomon Islands, often foraging nocturnally on fish and invertebrates in shallow waters. All three species exhibit sexual size dimorphism, with females larger than males, and are currently assessed as Least Concern by the IUCN due to their broad distributions, though local declines occur from habitat alteration and bycatch.

Physical Description

Morphology

Acrochordus species display a highly specialized morphology suited to their aquatic existence, characterized by robust, elongated bodies that facilitate movement through water. Across the three recognized , adult body lengths typically range from 60 cm to 243 cm, with smaller individuals and juveniles at the lower end and maximum sizes attained by females of larger species such as Acrochordus javanicus and . The body exhibits a stout trunk with a triangular cross-section, providing stability and hydrodynamic efficiency during . A defining feature is the loose, baggy that envelops the body, allowing significant expansion to accommodate large prey swallowed whole, a critical for their predation strategy in aquatic environments. This is covered uniformly by small, granular, non-overlapping scales on both dorsal and ventral surfaces, lacking the broad, overlapping ventral scutes typical of terrestrial snakes; instead, the ventral scales are comparable in and to the dorsals, forming a continuous, rugose texture. The head is short and blunt, without distinct enlarged shields, and features dorsally positioned eyes that are small and enable surface vision while the body remains submerged. Nostrils are similarly located on the dorsal anterior surface, equipped with valved flaps that seal during dives to prevent water ingress, supporting efficient respiration at the water's surface. Reflecting their fully aquatic lifestyle, Acrochordus lack external limbs entirely, relying on undulatory motions powered by the robust trunk and a laterally compressed that functions as a . In species like A. granulatus, the is notably paddle-like, enhancing maneuverability in shallow coastal waters.

Skin and Sensory Features

The skin of Acrochordus species features loose, baggy integument covered by numerous small, non-overlapping scales adorned with pyramidal or tubercular projections, creating a distinctive "file-like" rough texture that is unique to the family Acrochordidae. These projections, often referred to as scale sensillae, contribute to the dermal structure's overall coarseness, distinguishing Acrochordus from other snake families with imbricate or smoother scales. This rough texture also allows the skin to trap algae and sediment, providing effective camouflage in aquatic environments. The loose skin facilitates expansion, such as during prey ingestion, but also renders it susceptible to environmental stressors. In captive settings, the loose skin of Acrochordus increases vulnerability to bacterial infections, such as caused by , which can lead to systemic illness and death, thereby complicating husbandry efforts. Proper maintenance of , cleanliness, and is essential to mitigate these risks, as infections often arise from suboptimal enclosure conditions that promote proliferation on the permeable dermal surface. Acrochordus species have small eyes positioned dorsally on the head, which provide limited , especially in the murky environments they inhabit, leading to a greater dependence on tactile and chemical senses for and prey location. Chemical cues are detected via the and , while tactile sensitivity is enhanced by the rough, tubercular scales that respond to hydrodynamic disturbances. This sensory reliance compensates for the constraints of their ocular adaptations in low-visibility aquatic habitats. The skin of Acrochordus exhibits high permeability to , enabling passive in without the need to drink it, though individuals preferentially consume freshwater when accessible to restore hydration balance. This adaptation allows tolerance of saline environments, with thresholds reaching approximately 7-10% body mass loss before eliciting drinking responses, but underscores a physiological preference for freshwater to prevent osmoregulatory stress. The elevated cutaneous permeability, exceeding that of many terrestrial snakes, facilitates such exchanges but necessitates frequent access to potable in natural or captive conditions.

Distribution and Habitat

Geographic Range

The genus Acrochordus is native to tropical and subtropical regions of the , extending from and eastward through —including the , , , , , , , and —to , , and Pacific islands such as , Mussau, the , and the . The three species within the exhibit considerable overlap in their distributions, particularly in shared regions like (including , , , and Papua), , and coastal northern Australia ( and ), facilitating potential in coastal and estuarine zones. However, the genus is entirely absent from and the , with its range confined to the eastern and western Pacific basins. Records of introductions or vagrancy outside the native range are scarce and unconfirmed, including a single dubious report from Japan's Amami-Oshima Island in the Ryukyu Archipelago, with no evidence of established non-native populations. These snakes occupy aquatic habitats across their geographic extent.

Environmental Preferences

Acrochordus species exhibit a strong preference for slow-moving or stagnant aquatic environments, including freshwater rivers, streams, lowland lakes, ponds, swamps, floodplains, estuaries, and mangrove forests, where they spend their entire lives fully submerged. While A. arafurae and A. javanicus are primarily associated with freshwater and occasionally brackish habitats such as pandanus-lined lagoons and sheltered riverbanks, A. granulatus shows broader euryhaline tolerance, inhabiting coastal marine, estuarine, and mangrove systems but avoiding open oceanic waters of full salinity. All species demonstrate some capacity to tolerate brackish conditions and fluctuating salinities, though prolonged exposure to high marine salinity leads to dehydration, necessitating access to freshwater sources for osmoregulation and nitrogenous waste elimination. These snakes are closely associated with vegetated or muddy substrates, such as roots, sandy mud bottoms, beds, and burrows in soft sediment, which provide and sites for . They typically occupy shallow depths, often less than 10 meters, to facilitate frequent surfacing for air, though A. granulatus has been recorded up to 20 meters or deeper, including a record exceeding 30 meters as of November 2025. Acrochordus thrive in warm tropical waters with temperatures generally ranging from 25°C to 30°C, reflecting their distribution across and , but they are sensitive to water quality degradation, including and rapid salinity shifts, which can disrupt their physiological balance and serve as indicators of coastal .

Behavior and Ecology

Diet and Feeding Strategies

Acrochordus are primarily piscivorous, with a diet consisting almost exclusively of such as gobies (e.g., Oxyeleotris lineolatus), eels, and catfishes (e.g., leptaspis and Neosilurus hyrtlii), occasionally supplemented by crustaceans and snails. Larger individuals can consume up to 1 kg in weight, while smaller snakes target proportionally smaller prey, reflecting a prey size selection based on the snake's own body dimensions. These snakes are opportunistic feeders, readily consuming carrion such as dead when encountered. Feeding strategies in Acrochordus revolve around predation in aquatic environments, where the snakes remain sedentary on the substrate, waiting for prey to approach before striking. Their distinctive rough, tuberculate scales play a critical role in capturing slippery, mucus-covered by providing grip during seizure and , enabling the snakes to hold and swallow prey whole without reliance on or . This adaptation is particularly suited to their fully aquatic lifestyle in rivers, estuaries, and mangroves. Acrochordus exhibit a low metabolic rate compared to other reptiles, which supports infrequent feeding—typically every few weeks—allowing them to survive on sporadic large meals with high digestive efficiency. This energy-conserving physiology aligns with their sedentary behavior and the variable availability of prey in seasonal tropical habitats.

Reproduction

Acrochordus species exhibit ovoviviparous reproduction, in which eggs are retained within the oviducts and embryos develop internally, nourished by reserves until the female gives live birth. This mode ensures protection for developing young in the fully aquatic environment. sizes typically range from 5 to 25 young, varying by and maternal body size; for example, A. granulatus produces 1–8 offspring (mean ≈5–6), A. arafurae 11–25, and A. javanicus 13–52 (mean ≈29). Breeding is highly seasonal and synchronized with tropical wet seasons to optimize conditions for offspring survival, with ovarian activity peaking in summer months. In Australian populations of A. arafurae, ovulation occurs around July (late dry season), followed by a gestation period of approximately 5–6 months, culminating in births during the wet season (December–January). Similar patterns occur in Southeast Asian populations, where testicular enlargement and follicle development align with post-monsoon periods. Neonates emerge fully aquatic and independent, measuring 20–30 cm in total length at birth, capable of immediately without . is attained at 4–6 years of age or more, though this varies with growth rates influenced by the snakes' low metabolism, which also results in biennial or less frequent reproduction in many females.

Taxonomy and Evolution

Taxonomic Classification

The genus Acrochordus is classified within the Acrochordidae, a monogeneric family comprising solely this genus, which is placed in the suborder Serpentes of the order . The family Acrochordidae was established by in 1831, while the genus Acrochordus was originally described by Claes Fredrik Hornstedt in 1787. This classification reflects the unique morphological and ecological traits of these aquatic snakes, distinguishing them from other serpent lineages. Currently, three extant are recognized in the Acrochordus, with no acknowledged: A. arafurae McDowell, 1979; A. granulatus (Schneider, 1799); and A. javanicus Hornstedt, 1787. Historical taxonomic revisions have clarified synonyms and species boundaries; notably, A. arafurae was distinguished from A. javanicus in 1979 by Samuel B. McDowell based on differences in nostril orientation, scale counts around the eye, and labial morphology. Phylogenetically, Acrochordus occupies a basal position within , the clade of advanced snakes that also includes , but it is distinctly separated from the more derived colubroid families due to primitive traits such as specialized aquatic adaptations and cranial morphology. This placement underscores the genus's role as a foundational lineage in caenophidian , bridging earlier alethinophidian snakes and more specialized colubroids.

Evolutionary History

The genus Acrochordus first appears in the fossil record during the early Miocene, with the oldest known specimens dating to the Aquitanian stage (approximately 23–20 million years ago) from the Kharinadi Formation in Gujarat, western India. These fossils, consisting of vertebrae and ribs, exhibit morphological features indicative of an obligately aquatic lifestyle, such as elongated neural spines and robust zygapophyses adapted for undulatory swimming in fluviolacustrine environments. Additional fossil evidence from the Siwalik Group in Pakistan, spanning the middle to late Miocene (approximately 18–6.35 million years ago), includes over 1,200 vertebrae attributed to Acrochordus dehmi, a species larger than modern forms and dominant in aquatic depositional sites, suggesting early specialization to shallow-water habitats amid the intensification of the Asian monsoon system. No pre-Neogene fossils of Acrochordus have been identified in South Asia, constraining the lineage's origin to the Paleogene-Neogene boundary or slightly earlier, potentially linked to the dispersal of caenophidian snakes across Eurasia. Phylogenetically, Acrochordus occupies a basal position within the clade of advanced snakes, serving as the to the diverse superfamily, which encompasses most extant colubroid and viperid snakes. This relationship is supported by analyses of mitochondrial and nuclear DNA sequences, as well as morphological characters like the absence of advanced colubroid cranial specializations. The family Acrochordidae, containing only Acrochordus, has no close living relatives outside its own boundaries, highlighting its isolated evolutionary trajectory among aquatic squamates. Molecular phylogenetic studies, incorporating one mitochondrial locus () and two nuclear genes (c-mos and Rag-1), reveal that the three extant Acrochordus species diverged during the , with A. javanicus branching off first from the lineage leading to A. arafurae and A. granulatus around 20 million years ago, followed by the split between the latter two approximately 16 million years ago. These estimates, derived from Bayesian relaxed-clock analyses calibrated with fossils including A. dehmi (positioned as sister to A. javanicus), indicate deep interspecific divergences predating other marine snake radiations and aligning with tectonic events facilitating Indo-Australian dispersal. Key evolutionary adaptations in Acrochordus, such as and the development of rough, keeled with tubercular scales, likely emerged as responses to a fully aquatic niche, enabling live birth in water without terrestrial egg-laying and providing grip on slippery prey during . , observed across all , represents an independent origin within squamates, facilitating transfer via a simple suited to prolonged submersion. The dermal tubercles, unique among snakes, enhance friction in wet environments and may deter , underscoring the genus's specialization since its origins.

Species

Acrochordus arafurae

Acrochordus arafurae, commonly known as the Arafura file snake, is the largest species in the genus Acrochordus, endemic to southern (including and Indonesian Papua) and coastal regions of northern Australia, specifically the and . This aquatic snake can reach maximum lengths of up to 2.5 m, with females exhibiting extreme by growing significantly larger than males. The displays a distinctive brown or tawny coloration with minimal patterning, featuring an intricate network of dark reticulated markings that isolate small spots of ground color, providing effective in its aquatic environment. Like other members of the , it possesses loose, flabby covered in small, that give it a rough, file-like texture. It inhabits freshwater systems such as rivers, swamps, and billabongs, occasionally venturing into nearby estuaries and coastal waters, where it remains highly aquatic and nocturnal. A. arafurae is classified as Least Concern by the , with the assessment from 2017 indicating stable populations with no significant decline observed. The species is locally abundant across its range, though it faces potential threats from habitat degradation, pollution, and limited exploitation for its skin, which is used in traditional crafts like drum-making in .

Acrochordus granulatus

Acrochordus granulatus, known as the little file snake or marine wart snake, represents the smallest species within its , with adults typically attaining lengths of 60-80 cm. This compact, fully aquatic serpent exhibits a distinctive loose, baggy skin covered in small, that give it a rough, file-like texture, aiding in prey capture. Its distribution spans a broad coastal range from peninsular eastward through —including countries such as , , , , , and the —to and the , encompassing both brackish and marine environments along this extensive corridor. The species displays a mottled gray-brown dorsum accented by irregular black bands that widen on the back and narrow ventrally, providing effective in murky estuarine waters. It thrives in brackish estuaries and habitats, where its tolerance for varying salinities allows it to navigate tidal zones with ease. A. granulatus primarily preys on small fishes like gobies and such as crustaceans, ambushing them in shallow, vegetated areas using its specialized to grip slippery quarry. Classified as Least Concern by the in an assessment conducted on 18 October 2020, with no subsequent status change reported by , A. granulatus remains relatively abundant across much of its range. It is particularly common in the , where populations support local ecological dynamics in coastal fisheries. However, local declines occur due to incidental capture as in gillnets and trawls, particularly in Indian and Southeast Asian waters, posing a persistent threat despite its overall stable status. Like other acrochordids, A. granulatus is ovoviviparous, giving birth to live young in coastal waters.

Acrochordus javanicus

Acrochordus javanicus, commonly known as the Javan file snake or elephant trunk snake, is a fully aquatic species restricted to Southeast Asia, ranging from Vietnam and Cambodia through Thailand and peninsular Malaysia to Indonesia, including the islands of Sumatra, Java, and Borneo. This snake inhabits slow-moving freshwater and brackish environments such as rivers, swamps, streams, estuaries, and coastal lagoons, where it spends nearly its entire life submerged. Adults can attain a maximum total length of approximately 2.4 meters, with females significantly larger and more robust than males; the species exhibits pronounced in size. Its most distinctive feature is the loose, baggy, and deeply wrinkled skin, which imparts a trunk-like appearance and allows for expansion during feeding. The dorsal surface is typically brown, while the ventral side is pale yellow or cream-colored. As a carnivorous , A. javanicus primarily feeds on , including eels and catfishes, as well as occasional amphibians like frogs; it subdues prey by coiling around it rather than . The species is ovoviviparous, with females giving birth to live young in litters ranging from 13 to 52 , averaging 25 to 30, each measuring about 28 to 36 cm at birth. The International Union for Conservation of Nature (IUCN) classifies A. javanicus as Least Concern, based on a assessment indicating a wide distribution and stable populations despite localized pressures. However, habitat degradation from wetland drainage and pollution poses threats to regional subpopulations, particularly in densely populated areas like .

Conservation

Commercial Exploitation

Acrochordus species, particularly A. javanicus, have been commercially harvested primarily for their durable, rough-textured hides, which are processed into for products such as handbags, belts, and watch straps. The loose, granular skin structure provides a distinctive texture valued in the exotic leather trade, especially in . Harvesting occurs mainly through wild collection in wetlands and rivers, with skins exported from to markets in and . Prior to enhanced regulations in the early , annual trade volumes in were substantial, with estimates of around 330,000 A. javanicus individuals harvested yearly, often exceeding official quotas and contributing to population declines in heavily exploited areas. Historical has resulted in local rarity for some populations, particularly in and , where intensive fishing pressure depleted accessible habitats. Although not listed under Appendix I or II, Indonesia maintains a national export quota of 200,000 skins annually for A. javanicus. Captive maintenance of Acrochordus in zoos and aquariums presents significant challenges, including the snakes' reluctance to consume dead prey, which complicates feeding regimens and often leads to . They are also prone to skin infections due to their permeable, rugose and require precise humidity control to avoid , with losses up to 0.5% of body mass per day in suboptimal conditions. Few successful breeding programs exist, with limited records of in despite occasional successes in specialized facilities.

Status and Threats

The three species of Acrochordus—A. arafurae, A. granulatus, and A. javanicus—are all classified as Least Concern on the of , reflecting their relatively wide distributions across , , , and parts of the , though localized population declines have been noted in some areas due to environmental pressures. The assessments were last conducted in 2018 for A. arafurae, 2020 for A. granulatus, and 2011 for A. javanicus, with no changes to their status reported through 2025, indicating overall population stability despite regional vulnerabilities. Primary threats to these species stem from driven by and , which degrade essential forests and riverine systems across their ranges in and . in coastal fisheries, particularly gillnets and trawls, poses a significant risk, as these snakes are often incidentally captured and drowned during operations in brackish and marine environments. from agricultural runoff, industrial effluents, and urban waste further endangers their aquatic habitats by contaminating prey sources and altering water quality in rivers and estuaries. No major population crashes have been documented for any Acrochordus species, supporting their Least Concern designation, but ongoing monitoring is recommended, especially in Southeast Asian hotspots where is intensifying. Potential future risks include climate change impacts, such as rising sea levels and altered precipitation patterns that could shift salinity levels in mangroves and coastal rivers, potentially disrupting their osmoregulatory adaptations and breeding cycles. These threats underscore the need for targeted conservation efforts to protect coastal ecosystems vital to their survival.

References

  1. https://www.wikidata.org/wiki/Q752551
  2. https://species.wikimedia.org/wiki/Acrochordus_arafurae
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