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Acrochordus granulatusLittle filesnake, Marine File Snake

By Laken Cooper

Geographic Range

Little file snakes, also known as wart snakes, occur in aquatic habitats along coastal regions of southeast Asia, Indonesia, northern Australia, and surrounding islands. They are native to the Paleartic, Oriental and Australian regions. There is limited information as to whether little file snakes have been introduced into other regions, but their importance in the pet trade suggest that they are present in captivity in many regions of the world. (Beatty and et.al, 2004; Beletsky and Finlay, 2007)

Habitat

Like other species in the genus Acrochordus, little file snakes are fully aquatic. Unlike Javan wart snakes and Arafura snakes, which are strictly freshwater species, little file snakes can tolerate a broad range salinities, from salt to freshwater. Little file snakes have been found at depths ranging from 4 to 20 m, but generally prefer shallow water habitats because they must surface often for air. File snakes can stay completely submerged for hours at a time while hunting for prey and can withstand both slow and fast-moving currents. (Greene and Fogden, 1997; Lillywhite, 1989; Vitt, et al., 2001)

  • Range depth
    4 to 20 m
    13.12 to 65.62 ft

Physical Description

Little file snakes are non-venomous. They are considerably smaller than other members of the genus Acrochordus, but have the most striking appearance of any Acrochordus species. Little file snakes are typically brownish-gray, with white or yellow stripes. Average body mass ranges from 69 to 191 g, and body length ranges from 0.6 to 2.43 m. Little file snakes have a number of features that aid in swimming and in deterring predators. All snakes in the genus Acrochordus have flat tails and loose skin that allows them to flatten out, resembling highly venomous sea snakes. Little file snakes have triangular bodies and raised scales, for which the common name "file snake" was given. They have about 100 roughly-textured scales, which allows them to grip and constrict their prey. In addition, these snakes are covered both dorsally and ventrally by tubercles, which allow them to quickly grasp onto plants and rocks, preventing them from being carried away by currents, and helping them to hold onto prey. Little file snakes also have nostrils located on the top of the head, which allows them to breathe without raising their head completely out of the water. Unlike land snakes, the lungs of file snakes extend throughout their body, so that they are able to stay submerged in water for hours without coming up for air. Like other reptiles, file snakes are ectotherms, resulting in a low metabolism. This also allows them to remain submerged for long periods of time. Like other snakes, little file snakes shed their skin during growth. Although terrestrial snakes use rocks and other hard surfaces to help pull off their old skin, little file snakes are highly active in the days prior to shedding. Increased activity rates results in decreased mass and helps loosen their old skin prior to shedding. (Lillywhite, 1989; Lillywhite, 1996; Lillywhite, et al., 1988; Marais, 2007; Vitt, et al., 2001)

File snakes are sexually dimorphic. Females are typically larger than males, with a larger head and longer and heavier body. These larger body proportions help to support the reproductive processes. Average snout to vent length (SVL) in adult females is 686.2 mm, whereas average SVL in males is 648.6 mm. Body weight averages 168.5 g for females and 104 g for males. Females have an average head length of 19.57 mm and an average head width 13.2 mm. Males have an average head length of 17.8 mm and an average head width 11.11 mm. (Rieppel and Zaher, 2001; Sanders, et al., 2010; Voris and Glodek, 1920)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range mass
    69 to 191 g
    2.43 to 6.73 oz
  • Range length
    0.6 to 2.43 m
    1.97 to 7.97 ft
  • Average length
    1 m
    3.28 ft

Development

Unlike most snakes, little file snakes are ovoviviparous. Embryos do not contain a skull and have very few other developed organs. Little file snakes have indeterminate growth. The metotic fissure, a bony canal connecting the inner ear to the brain case that helps transmit stimuli to the nervous system, is present in all snakes except members of the genus Acrochordus. This simple autapomorphy suggests that acrochords are only distantly related to other groups of snakes. (Lillywhite, 1989; Rieppel and Zaher, 2001; Sanders, et al., 2010; Voris and Glodek, 1920)

Reproduction

Only limited information exists regarding the mating system of little file snakes. Females release pheromones in order to attract males, and in many cases multiple males arrive. It is not known how females choose a mate, since there is no competition among male file snakes. In sea snakes, males wrap around the larger females to begin the mating process. Mating may last for hours. Some males drown during mating, as females determine when the pair surfaces for air. Male snakes have two penises, but can only mate with one at a time. (Cermak, 2008; Christiansen, 2009)

Acrochordus granulatus mates once every 2 years, typically during June or July. Gestation ranges from 5 to 7 months. Males produce sperm throughout the year, which moves through the ductus to the cloaca during mating periods. Sperm levels vary depending on time of year and typically increases as mating approaches. Female file snakes accumulate yolk in high amounts during mating season. Females are capable of delaying conception and holding sperm until conditions are suitable for giving birth. (Houston and Shine, 1994; Mattison, 1995)

No information is available on sexual maturation in Acrochordus granulatus. In closely related Acrochordus arafura, males become sexually mature as early as 4 years old, with an average age of maturation closer to 5 years. Most A. arafura females reach sexual maturity by 7 years of age. Acrochordus granulatus has clutch sizes ranging from 1 to 12 eggs, with an average of 6 eggs, and birth mass ranges from 6 to 9 g. (Houston and Shine, 1994; Mattison, 1995)

  • Breeding interval
    Little file snakes breed once every two years.
  • Breeding season
    Little file snakes breed during June and July and give birth during December.
  • Range number of offspring
    1 to 12
  • Average number of offspring
    6
  • Range gestation period
    5 to 7 months

Neither male or female little file snakes provide parental care for young. Offspring are completely independent upon birth. (Houston and Shine, 1994)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

In captivity, the lifespan of Acrochordus granulatus ranges from 3 to 5 years. This short lifespan is due to their specialized needs for a warm environment and a steady supply of live prey. Other species in the genus Acrochordus live slightly longer in captivity. Acrochordus arafura has been reported to live nearly 9 years, and A. javanicus approximately 6 years. There is no information available regarding the lifespan of this species in the wild. (Houston and Shine, 1994; Lillywhite, 1996; Mattison, 1995)

  • Typical lifespan
    Status: captivity
    3 to 5 years

Behavior

Little file snakes are nocturnal and spend a majority of their time hunting and swimming. During the day, they spend their time burrowed in the mud or in sea grass. When submerged, they can go several hours without surfacing for air. File snakes are fully aquatic, however, during high tides they may come on land to move into shallow pools of water. (Lillywhite and Ellis, 1994; Lillywhite, 1996; Shine, 1991)

Little file snakes may live in groups and burrow together, but do not communicate with one other as some species do and are not known to have an established social hierarchy, even during the mating season. Little file snakes are not aggressive towards one another. When kept as pets, as many as 10 individuals may share an aquarium without displays of aggressive behaviors. They typically hunt as individuals; however, captive individuals may feed as a group when fish prey are provided. (Lillywhite, 1996)

Home Range

There is no information available on the average home range size of little file snakes.

Communication and Perception

Outside of breeding season, little file snakes do not communicate with conspecifics. During breeding season females produce pheromones in order to attract potential mates, which detect this pheromone via Jacobson't organ. Like terrestrial snakes, little file snakes use their tongues to detect danger and to locate prey via olfaction. Most snakes have advanced haptic and auditory senses and limited vision, however, these have not been formally tested in little file snakes. (Deoras, 1965; Lillywhite, 1996)

Food Habits

File snakes are piscivores and their diet primarily consists of small fish, snails, and small crustaceans. More specifically, little file snakes prey heavily on sleeper fish and gobies. (Lillywhite, 1996; Voris and Glodek, 1920)

File snakes exhibit sexually dimorphic feeding behavior. Males locate food by sliding along the bottom of the ocean floor and searching in cracks for fish. Females are ambush predators and wait for prey to pass by before attacking. Both sexes have rough skin that helps them keep hold of prey. File snakes do not store food in their body, but digest it as soon as it is caught. (Lillywhite, 1996; Shine, 1991; Voris and Glodek, 1920)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

File snakes have a number of anti-predator adaptations, which are used not only to deter predators, but also serve as adaptations for surviving in an aquatic environment. During the day, they spend much of their time in the shelter of underwater grasses and mud. In addition to olfaction, little file snakes use their forked-tongue as a way to sense potential threats. They also have relatively loose skin, which allows them to flatten their bodies and move more efficiently in the water when escaping potential predators. Major predators of little file snakes include humans, which hut them for their meat, crocodiles, and sea eagles. (Deoras, 1965; Lillywhite and Ellis, 1994; Lillywhite, 1989)

Ecosystem Roles

As a piscivore, Acrochordus granulatus likely has a significant impact on local fish diversity and abundance. They are also prey for a number of different vertebrate predators throughout their geographic range. Parasites of this species have not been documented. (Mattison, 1995)

Economic Importance for Humans: Positive

Humans hunt little file snakes for their meat and for trade on the aquaria market. Occasionally, they are also captured for their skin, which can be used as a substitute for leather to make handbags, shoes, wallets and a number of other items. (Lillywhite, 1996; Shine, 1991)

  • Positive Impacts
  • pet trade
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Acrochordus granulatus on humans. (Shine, 1991)

Conservation Status

Little file snakes have a broad geographic range and are locally abundant. Populations are considered stable, and there are no known threats to the longterm persistence of this species. Their ability to survive in a variety of aquatic environments allows them to tolerate environmental changes reasonably well. (Feder, 1980; Lillywhite, et al., 1988)

Contributors

Laken Cooper (author), Radford University, Christine Small (editor), Radford University, John Berini (editor), Animal Diversity Web Staff.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Palearctic

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

World Map

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

food

A substance that provides both nutrients and energy to a living thing.

fossorial

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

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

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).

natatorial

specialized for swimming

native range

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

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

ovoviviparous

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

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

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

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

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

social

associates with others of its species; forms social groups.

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

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).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Beatty, R., et.al. 2004. Encyclopedia of the Aquatic World. Tarrytown, NY: Marshall Cavendish Corporation.

Beletsky, L., H. Finlay. 2007. Australia: The East. Northampton, Massachusetts: Interlink Publishing Group.

Cermak, M. 2008. Spectacular Snakes of Australia. Cullingwood, Australia: Csiro Publishing.

Christiansen, P. 2009. Constrictor Snakes. London, U.K.: Amber Book, Ltd.

Deoras, P. 1965. Snakes of India. New Delhi, India: National Book Trust.

Dunson, W., S. Minton. 1978. Diversity, distribution, and ecology of Philippine marine snakes. Journal of Herpetology, 12/3: 281-286.

Feder, M. 1980. Blood oxygen stores in the file snake, Acrochordus granulatus, and in other marine snakes. Physiological Zoology, 53/4: 394-401.

Greene, H., M. Fogden. 1997. Snakes: The Evolution of Mystery in Nature. London, England: University of California Press.

Houston, D., R. Shine. 1994. Low growth rates and delayed maturation in Arafura file snakes (Serpentes: Acrochordidae) in tropical Australia. American Society of Ichthyologists and Herpetologists, 1994/3: 726-731.

Hutchins, M. 2003. Family: File Snakes. Pp. 439-444 in Animal Life Encyclopedia, Vol. 7, 2 Edition. Farmington Hills, MI: Gale Group, Inc.

Lemen, C., H. Voris. 1981. A comparison of reproductive strategies among marine snakes. Journal of Animal Ecology, 50: 89-101.

Lillywhite, H. 2003. "File Snakes" (On-line). Accessed February 13, 2011 at http://www.novelguide.com/a/discover/grze_07/grze_07_00475.html.

Lillywhite, H. 1996. Husbandry of the little file snake, Acrochordus granulatus. Zoo Biology, 15/3: 315-327.

Lillywhite, H. 1989. Unusual shedding behaviors in an aquatic snake, Acrochordus granulatus. Copeia, 1989/3: 768-770.

Lillywhite, H., T. Ellis. 1994. Ecophysiological aspects of the Coastal-Estuarine distribution of Acrochordid snakes. Coastal and Estuarine Research Foundation, 17/1: 53-61.

Lillywhite, H., A. Smits, M. Feder. 1988. Body fluid volumes in the aquatic snake, Acrochordus granulatus. Journal of Herpetology, 22/4: 434-438.

Marais, J. 2007. What's that Snake?. Cape Town, South Africa: Struik Publishers.

Marshall, A., B. Beehler. 2007. The Ecology of Papua. North Clarendon, VT: EricOey.

Mattison, C. 1986. Snakes of the World. New York, NY: Facts on File, Inc.

Mattison, C. 1995. The Encyclopedia of Snakes. New York, NY: Facts on File, Inc.

Rieppel, O., H. Zaher. 2001. The development of the skull in Acrochordus granulatus (Schneider) (Reptilia: Serpentes), with special consideration of the Otico-Occipital complex. Journal of Morphology, 249/3: 252-266.

Sanders, K., Mumpuni, A. Hamidy, J. Head, D. Gower. 2010. Phylogeny and divergence times of file snakes (Acrochordus): Inferences from morphology, fossils and three molecular loci. Molecular Phylogenetics and Evolution, 56/3: 857-867.

Shine, R. 1991. Australian Snakes: A Natural History. Ithaca, New York: Reed Books.

Vitt, L., J. Caldwell, G. Zug. 2001. Herpetology. San Diego, California: Academic Press.

Voris, H., G. Glodek. 1920. Habitat, diet and reproduction of the file snake, Acrochordus granulatus, in the Straits of Malacca. Journal of Herpetology, 14/1: 108-111.

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