Congolese giant toads may mimic venomous snakes to trick predators

Congolese giant toads may have mastered a way to fake out would-be predators looking for a tasty burger-sized snack. With a hiss and a butt-up posture that displays their backside, the toads look — and sound — remarkably like venomous vipers that slither through the same habitat.

These toads (Sclerophyrs channingi) may be using mimicry to avoid becoming other animals’ lunch, researchers report October 20 in the Journal of Natural History. If so, this would be the first known example of a toad imitating a venomous snake. 

One of the largest vipers in Africa, the Gaboon viper (Bitis gabonica), sports “the longest fangs of any snake in the world” — roughly 5 centimeters, says study coauthor Eli Greenbaum, a herpetologist and evolutionary geneticist at the University of Texas at El Paso. The snakes’ venom isn’t very toxic, but they can inject enough of it to make for lethal encounters.

An analysis of 10 Gaboon vipers and 16 Congolese giant toads from museum collections revealed that the toad’s body resembles the viper’s head in color pattern and size. By raising its rump, the toad “shows off this color pattern and shape that looks kind of like the cocked head of a Gaboon viper that’s preparing to strike,” Greenbaum says. And when handled, the toad makes a noise like a balloon letting out air that’s similar to the viper’s wheezy hiss.

These toads, endemic to Congo, have so far been found only in places there where the snake also lives. DNA analyses of the viper and toad by other scientists suggest that the two species emerged around the same time and may have evolved together.  

So far, “all of that evidence combined suggests that there’s a pretty strong case that these toads are mimicking these vipers,” Greenbaum says. Proving it would require testing if would-be toad eaters are, in fact, duped.