Step aside octopodes, there is a new master of camouflage in the animal kingdom. Certainly, Congolese giant toads don't have the capacity to change color to blend in with any background that some cephalopods manage, but they win points for originality. It's certainly common for vulnerable creatures to take on the appearance of something far more fearsome to avoid being eaten, but an amphibian pretending to be a snake is novel.
Nevertheless, that is exactly what Dr Eli Greenbaum of the University of Texas, El Paso, and colleagues describe in the Journal of Natural History. The toad's coloring resembles that of the Gaboon viper, particularly the dark brown spots and stripe on the toad's body and viper's head and a sharp color change from the toad's back to flank. The toad also has unusually smooth skin considering it belongs to a group of amphibians known for their bumpiness.
Furthermore, herpetologist Dr Chifundera Kusamba of the DRC's Centre de Recherche en Sciences Naturelles described hearing the toad make a sound he compared to air being released from a balloon, which also resembles the hissing sound the viper makes before making a defensive strike. A century ago American biologist James Chapin described seeing the toad “bow” in a way that would hide its legs.
“Our study is based on 10 years of fieldwork and on direct observation by researchers lucky enough to see the toad’s behaviour first-hand. We’re convinced that this is an example of Batesian mimicry, where a harmless species avoids predators by pretending to be a dangerous or toxic one,” Greenbaum said in a statement.
Greenbaum acknowledges proof of mimicry requires evidence the toad's predators are sometimes fooled. This is lacking because the toad is rarely seen in its native habitat, which, as its name suggests, is the rainforest of central Africa. It would take a lot of time or luck to witness one scaring off a threat.
The toad's range is small, perhaps because, when you are a legged species pretending to be one without, you can't fool all the predators all the time. Nevertheless, it has never been recorded where the vipers are unknown, so it probably helps.
“Given the relatively large size and therefore calorific value of this toad compared to other species, it would make tempting prey to a large variety of generalist predators, including primates and other mammals, lizards, snakes and birds,” Kusamba said.
If you're going to pretend to be something dangerous, the Gaboon viper is not a bad choice. Its 5-centimeter (2-inch) fangs are the longest in the snake world and it uses them to deliver the largest load of venom. Although the venom is not as lethal, gram for gram, as that of many other snakes, the viper's bite has been described as the world's most painful. We don't know who volunteered to compare but the toad's predators have reason to choose caution.