By chewing on the bark of a poisonous tree, the African crested rat acquires a toxin that it delivers if bitten by predators — the first placental mammal found to combat predation in this way.

Credit: R. SOC.

When threatened, the rat (Lophiomys imhausi) parts its grey fur to expose a pattern of specialized black and white hairs on its flanks (pictured), daring its attacker to bite the target. The creature picks up the toxin with its saliva by gnawing on the Acokanthera schimperi tree, then drools on the hairs.

Fritz Vollrath at the University of Oxford, UK, and his colleagues examined the structure of these hairs under two types of electron microscope. They found the hairs to be porous cylinders enclosing many long fibrils — a structure well adapted to absorbing the toxin and to delivering it upon contact with a predator's mouth.

Proc. R. Soc. B 10.1098/rspb.2011.1169 (2011)