The secret life of a fanged frog with an enormous head

The rainforests of Vietnam and Cambodia are home to a strange species of Fanged Frog (Limnonectes dabanus). Along with sporting 'fangs' on their lower jaw, males of the species have enormous, strangely shaped heads. Despite their curious appearance, very little is known about these frogs, and for the first time we document their rather weird breeding biology and advertisement call.

At night during the rainy season, the rainforests of Southeast Asia erupt with the sound of frogs. Flying Frogs make soft clicking noises from the canopy, tiny tree frogs whirr from the branches above, and torrent frogs whistle from the boulders along swift flowing streams. But the call of the Fanged Frog Limnonectes dabanus was a mystery, until now.

Limnonectes dabanus is a medium-sized, ground-dwelling frog from the rainforests of Cambodia and southern Vietnam. Like other frogs in this group, the species has prominent ‘fangs’ (odontoids) on their lower jaw- hence the name ‘fanged frog’.

Aside from the fangs, female frogs look pretty normal. Male frogs are the really weird ones. The head of male frogs make up nearly half their body length, and they have head “ornamentation” in the form of a swollen cap, or caruncle, on the top of their heads. They’re also much larger than females.

So what does this impressive frog sound like when it calls? During our fieldwork in the forests of Vietnam we came accross a couple of calling male Limnonectes dabanus and managed to record their calls (while ankle-deep in mud!). Their call sounds a bit like a large water drop falling into a pool of water. What’s even more impressive is that it makes the noise without a vocal sac, the flexible membrane of skin possessed by most male frogs that serves to amplify their advertisement call.

We found that Limnonectes dabanus breeds in shallow, non-flowing or slow-flowing pools, puddles, and drainage ditches. Eggs and tadpoles of the species are pretty normal, but in one case, we found the eggs of the species scattered all over a small cave- on the floor, and stuck to the walls and roof. We’re really not sure how the couple managed that!

And what about the massive head of the males? Well, it may be used in male combat- for fighting with other males for good breeding spots. Their head would make a formidable weapon (especially with the hard 'cap' and ‘fangs’). Indeed, males of other closely related species have been reported to butt heads with each other (and bite!) during combat.

Limnonectes dabanus is an amazing, but still very poorly-known frog. While our discoveries provide important insights into the breeding biology and habitat requirements of the species (and allow us to know if it's in a patch of forest just by hearing the call), there’s still so much we don’t know. Like almost a third of all amphibians in the region, Limnonectes dabanus is considered ‘Data Deficient’, meaning that we know so little about the species that we don’t even know if it’s threatened with extinction or not. Unfortunately, given the threats facing amphibians in the region (primarily habitat loss), it’s likely that it is.

Dr Jodi Rowley
Curator, Amphibian & Reptile Conservation Biology

More information:
Rowley, J. J. L., Le, T.T.D, Hoang, H. D. & Altig, R. (2014). The breeding behaviour, advertisement call and tadpole of Limnonectes dabanus (Anura: Dicroglossidae). Zootaxa. 3881(2):195-200.