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Cerberus rynchopsNew Guinea bockadam, Dog-faced Water Snake

By Helen Jewart

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)

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)

  • 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)

  • 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)

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

  • 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)

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)

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)

  • 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

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

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)

Contributors

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

Glossary

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

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.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

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.

freshwater

mainly lives in water that is not salty.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

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).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

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

nomadic

generally wanders from place to place, usually within a well-defined range.

oriental

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

World Map

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

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

solitary

lives alone

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

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.

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