Walking around the Chitengo Camp in Gorongosa, especially after the rain when the earth is soft, I often run into two types of cute, pig-like creatures. Warthogs are the more noticeable ones, digging around for roots and grubs, completely unafraid of the busy activity of the preparations for the opening of the tourist season. But if I look carefully at the ground under my feet I often see what appears to be another kind of a tiny, fat piglet. These are Shovel-nosed frogs (Hemisus marmoratus), a species of subterranean amphibians that are remarkably adept at digging into the soil. A closer look reveals the root of their scientific name (“hemi-” means “half” in Greek and “sus” is “a pig” in Latin) – their pudgy little body ends in a sharp snout and, unlike other burrowing frogs that dig with their hind feet, these dive in head first, using the snout as a wedge and their short legs to push the body underground. They are not great jumpers and so they prefer to run if scared, and as soon as they find a suitable patch of soil they start pushing the potbellied body into the earth. If the soil is soft they completely disappear in a matter of seconds.
Photo: Although officially known as the Shovel-nosed frog (Hemisus marmoratus), I think you will agree that a direct translation of its scientific name, the Marbled half-piglet, is more appropriate.
Often, however, the ground is too hard to dig, and the only choice is to stand their ground. Already quite portly, they gulp in air and inflate the body, turning it into a small balloon, and making it difficult to swallow by a snake or another predator.
Photo: The preferred mode of escape of the Shovel-nosed frog is to disappear underground. Their pointy snout and powerful hind legs allow them to dig in completely in only a few seconds.
The Shovel-nosed frogs feed mostly on termites and ants, which explains their exceptionally small mouth, but it is not clear whether they are able to feed underground or only on the surface. Their reproductive biology is quite interesting – rather than laying eggs directly in the water, the female lays them in a burrow a few weeks before the onset of rains, and waits for the wet season to come. During this time she defends the eggs and newly hatched tadpoles against ants and other predators. If the conditions allow she then digs a connecting channel to a larger pond where the tadpoles complete their development, or carries them there on her back. This strategy gives the tadpoles an edge over other species because they enter the water and begin feeding before the eggs of other frogs have a chance to hatch.
Photo: If unable to dig, the Shovel-nosed frog inflates its body, making itself difficult to swallow.
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