Acrochordus granulatusLittle filesnake, Marine File Snake

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.