Animal Diversity Web

Ge­o­graphic Range

Cer­berus ryn­chops be­longs to the fam­ily Homa­lop­si­dae, which refers to Indo-Aus­tralian rear-fanged water snakes. It is con­sid­ered one of the most widely dis­trib­uted of the Homa­lop­si­dae, found oc­cu­py­ing both Ori­en­tal and Aus­tralian re­gions from India to Wal­lacea. (Al­faro, et al., 2004; Brischoux, et al., 2012)

• Biogeographic Regions
• oriental
  • native
• indian ocean
  • native

Habi­tat

Bock­adams live in near-shore coastal wa­ters in­clud­ing ma­rine, brack­ish, and fresh­wa­ter en­vi­ron­ments. Their habi­tats are mostly man­grove forests, tidal mud­flats, and es­tu­ar­ine areas. They will also travel on sandy beaches, but they spend the ma­jor­ity of their life in some type of water. Salt glands are what allow them to live in ma­rine en­vi­ron­ments be­cause they can expel salt through them in order to sur­vive. Asian bock­adams are the only homa­lop­sid species known to have one, which makes them the most wide­spread Homa­losid. How­ever, their salt glands are less ef­fec­tive than other sea snakes and so they have a much more lim­ited range com­pared to groups like the Hy­drophi­inae (coral reef snakes). Asian mud snakes also tend to avoid deep water, un­like other ma­rine snakes. (Al­faro, et al., 2004; Brischoux, et al., 2012; Rah­man, et al., 2014; Ras­mussen, et al., 2011)

• Habitat Regions
• tropical
• saltwater or marine
• freshwater

• Aquatic Biomes
• pelagic
• benthic
• temporary pools
• coastal
• brackish water

• Other Habitat Features
• estuarine
• intertidal or littoral

• Range depth

  15 (high) m

  49.21 (high) ft

Phys­i­cal De­scrip­tion

Asian bock­adams are char­ac­ter­ized by a wide head and snout, which is where the ep­i­thet "dog-faced water snake" comes from. They are striped and dark brown with a white un­der­belly. On both sides of their head, they have Du­vernouy's glands which are the sub­ject of on­go­ing de­bate and re­search. It's pos­si­ble they are prim­i­tive venom glands which helps with swal­low­ing and are mildly ven­omous. Cer­berus ryn­chops is also opistho­glyp­hous, mean­ing they have an en­larged pair of teeth be­hind the max­imille that point back­wards. Most aquatic snakes, in­clud­ing bock­adams, have more flat­tened tails and very small scales which allow them to swim bet­ter. (Al­faro, et al., 2004; Jayne, et al., 1988; Mori, 1998)

One unique adap­ta­tion of homa­lop­sids is their valvu­lar nos­trils. Their glot­tis can ex­tend to the in­ter­nal nares, cre­at­ing a water tight seal which al­lows them to live un­der­wa­ter with­out drink­ing or in­hal­ing too much liq­uid. (Rah­man, et al., 2014)

• Other Physical Features
• ectothermic
• bilateral symmetry
• venomous

• Sexual Dimorphism
• female larger

• Range mass

  15 to 270 g

  0.53 to 9.52 oz

• Average mass

  105 g

  3.70 oz

• Range length

  20 to 80 cm

  7.87 to 31.50 in

• Average length

  55 cm

  21.65 in

De­vel­op­ment

Dog-faced water snakes are one of the few vi­vip­a­rous snakes, so they are born live in water. (Al­faro, et al., 2004; Jayne, et al., 1988; Mori, 1998)

Re­pro­duc­tion

Asian bock­adam mat­ing sys­tems re­main largely a mys­tery, but they are likely com­pa­ra­ble to sea snakes in north­ern Aus­tralia which mate in the win­ter. Males com­pete for fe­males at­ten­tion by chas­ing them through the water using fast zigzag move­ments. (Lynch, et al., 2021; Ras­mussen, et al., 2011)

• Mating System
• polygynous

Not a lot is known about the re­pro­duc­tion process, how­ever they are vi­vip­a­rous. (Mori, 1998; Ras­mussen, et al., 2011)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

• Breeding interval

  Homalopsid snakes are thought to breed every two years.

• Range number of offspring

  2 to 40

• Average number of offspring

  5

Once young bock­adams are born, they are in­de­pen­dent from their par­ents. (Ras­mussen, et al., 2011)

• Parental Investment
• no parental involvement
• precocial
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

There is very lit­tle re­search on the lifes­pan of any Homa­lop­sid snakes. How­ever, the longevity of a com­pa­ra­ble species (a coral reef snake) in cap­tiv­ity is 7 years.

• Range lifespan
  Status: captivity

  7 (high) years

Be­hav­ior

Cer­berus ryn­chops is a soli­tary species that spends most of it's time hunt­ing fish and mov­ing be­tween dif­fer­ent salt and fresh­wa­ter areas. They gen­er­ally stay within 50km of the shore­line in areas with warm an­nual tem­per­a­tures and lower, but vari­able salin­ity. (Brischoux, et al., 2012; Rah­man, et al., 2014)

• Key Behaviors
• natatorial
• motile
• nomadic
• solitary

Com­mu­ni­ca­tion and Per­cep­tion

Just like most snakes, bock­adams do not see well, so they in­ter­act with their en­vi­ron­ment mostly based on smell and touch. Snakes use an organ in the roof of their mouths to iden­tify chem­i­cals around them. (Al­faro, et al., 2004)

• Communication Channels
• tactile
• chemical

Food Habits

Asian bock­adams are pis­c­viv­o­rous and mostly in­gest fish head first. This re­duces any po­ten­tial re­sis­tance from the prey's limbs and re­duces swal­low­ing time. While more gen­er­al­ist water snakes have been ob­served com­ing on land to swal­low and di­gest, C. ryn­chops swal­low their prey un­der­wa­ter. Their prey con­sists mostly of fish, but they have also been ob­served eat­ing crus­taceans, and frogs. The fish they eat in­cludes go­b­ies, apogo­nids, siganids, oxy­dercine go­b­ies, cat­fish, mul­let, and eels. While feed­ing, they will often an­chor them­selves or swim back­wards in order to re-clamp the jaw around strug­gling prey. There's a pe­riod of prey hold­ing be­fore con­sump­tion which is as­sumed to be the time it takes for the venom to kill or im­mo­bi­lize prey. (Jayne, et al., 1988; Mori, 1998; Rah­man, et al., 2014)

• Primary Diet
• carnivore
  • piscivore
  • eats non-insect arthropods

• Animal Foods
• amphibians
• fish
• aquatic crustaceans

Pre­da­tion

The two main anti-preda­tor adap­ta­tions are cam­ou­flage and venom. Mud snakes adapted to blend into their habi­tat: mud. Their drawl brown, striped ap­pear­ance helps them blend in with shal­low, murky wa­ters and man­grove forests. Venom is their sec­ond de­fense, they will bite and in­ject venom into some­thing they per­ceive as a threat. (Ras­mussen, et al., 2011; Voris and Mur­phy, 2002)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • tiger shark (Caracharhinus caustus), pariah kite (Milyus migrans), mangrove crabs (Scylla serrata), Humans (Homo sapiens)

Ecosys­tem Roles

The main role of Cer­berus ryn­chops is as a preda­tor. They con­trol fish and am­phib­ian pop­u­la­tions in salt marshes, man­groves, and es­tu­ar­ies. (Jayne, et al., 1988)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Bock­adams are hunted as part of the in­ter­na­tional in­ter­est in rep­tile skin, or­gans, and meat, but they are also of spe­cial in­ter­est along with other aquatic snakes due to their venom.

They also serve vital ecosys­tem func­tions of con­trol­ling fish and am­phib­ian pop­u­la­tions. (Ras­mussen, et al., 2011)

• Positive Impacts
• food
• body parts are source of valuable material
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

The main ad­verse ef­fect on hu­mans is harm­ing them through ven­omous bites. Fish­er­men are the most com­mon vic­tims, es­pe­cially when han­dling nets that have been trawled or dragged in muddy coast­lines or es­tu­ar­ies. (Ras­mussen, et al., 2011)

• Negative Impacts
• injures humans
  • venomous

Con­ser­va­tion Sta­tus

Dog-faced mud snakes are not legally en­dan­gered under CITES or any other in­ter­na­tional list. How­ever, they are under un­eval­u­ated threat due to hunt­ing, by­catch, and pol­lu­tion. There are na­tional and in­ter­na­tional laws im­pact­ing the trade of their skin, or­gans, and meat. (Ras­mussen, et al., 2011)

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

Helen Je­w­art (au­thor), Col­orado State Uni­ver­sity, Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

"Cer­berus ryn­chops" (On-line). The Rep­tile Data­base. Ac­cessed Feb­ru­ary 20, 2022 at https://​reptile-database.​reptarium.​cz/​species.​php?​genus=Cerberus&​species=rynchops.

Al­faro, M., D. Karns, H. Voris, E. Aber­nathy, S. Sell­ins. 2004. Phy­logeny of Cer­berus (Ser­pentes: Homa­lopsi­nae) and Phy­lo­geog­ra­phy of Cer­berus ryn­chops: Di­ver­si­fi­ca­tion of a Coastal Ma­rine Snake in South­east Asia. Jour­nal of Bio­geog­ra­phy, Vol.31, No.8: 1277-1292.

Bern­stein, J., J. Mur­phy, H. Voris, R. Brown, S. Ruane. 2021. Phy­lo­ge­net­ics of mud snakes (Squa­mata: Ser­pentes: Homa­lop­si­dae): A para­dox of both un­de­scribed di­ver­sity and tax­o­nomic in­fla­tion. Mol­e­c­u­lar Phy­lo­ge­net­ics and Evo­lu­tion, Vol.160: 107109. Ac­cessed Feb­ru­ary 20, 2022 at https://​www.​sciencedirect.​com/​science/​article/​abs/​pii/​S1055790321000427?​via%3Dihub.

Brischoux, F., R. Tin­gley, R. Shine, H. Lil­ly­white. 2012. Salin­ity in­flu­ences the dis­tri­b­u­tion of ma­rine snakes: im­pli­ca­tions for evo­lu­tion­ary tran­si­tions to ma­rine life. Ecog­ra­phy, Vol.35, No.11: 994-1003. Ac­cessed Feb­ru­ary 20, 2022 at http://​www.​proquest.​com/​docview/​1125268689/​abstract/​17E866ACAA4C469APQ/​1.

Jayne, B., H. Voris, K. Heang. 1988. Diet, feed­ing be­hav­ior, growth, and num­bers of a pop­u­la­tion of Cer­berus ryn­chops (Ser­pentes: Homa­lopsi­nae) in Malaysia. Chicago: Field Mu­seum of Nat­ural His­tory.

Karns, D., A. O'Ban­non, H. Voirs, L. Weigt. 2000. Bio­geo­graph­i­cal Im­pli­ca­tions of Mi­to­chon­dr­ial DNA Vari­a­tion in the Bock­adam Snake (Cer­berus ryn­chops, Ser­pentes: Homa­lopsi­nae) in South­east Asia. Jour­nal of Bio­geog­ra­phy, Vol.27, No.2: 391-402. Ac­cessed Feb­ru­ary 20, 2022 at https://​www.​jstor.​org/​stable/​2656268.

Lynch, T., R. Al­ford, R. Shine. 2021. Mis­taken iden­tity may ex­plain why male sea snakes (Aipy­su­rus lae­vis, Elap­i­dae, Hy­drophi­inae) “at­tack” scuba divers. Sci­en­tific Re­ports, Vol.11, No.1: 15267.

Mori, A. 1998. Prey-Han­dling Be­hav­ior of Three Species of Homa­lop­sine Snakes: Fea­tures As­so­ci­ated with Pis­civory and Du­ver­noy's Glands. Jour­nal of her­petol­ogy, Vol. 32, Iss. 1: 40-50.

Rah­man, S., A. Reza, R. Datta, C. Jenk­ins, L. Luiselli. 2014. Niche par­ti­tion­ing and pop­u­la­tion struc­ture of sym­patric mud snakes (Homa­lop­si­dae) from Bangladesh. The Her­peto­log­i­cal Jour­nal, Vol. 24, No. 2: 123-128.

Ras­mussen, A., J. Mur­phy, M. Ompi, J. Gib­bons, P. Uetz. 2011. Ma­rine Rep­tiles. PLoS One, Vol.6, Iss.11.

Voris, H., J. Mur­phy. 2002. The prey and preda­tors of Homa­lop­sine snakes. Jour­nal of Nat­ural His­tory, Vol.36, No.13: 1621-1632.