Olfactory Obfuscation

An ambush-hunting species is difficult to sniff out.

A meerkat (Suricata suricatta) samples the odor from a scented cloth housed in a sample tube.

Shivan Parusnath, Wits University

Puff adders, Bitis arietans, lie in wait to catch their prey. These ambush hunters are visually camouflaged, but ecophysiologist Graham J. Alexander and his research lab at the Wits School of Animal, Plant and Environmental Sciences in Johannesburg, South Africa, began to suspect that puff adders might also be able to mask their scent, an additional trait that would give them considerable advantage over prey and protection from predators. The researchers had observed that dogs and tame mongooses—both snake predators that rely on their keen sense of smell to hunt—had failed to notice puff adders in the wild, even when walking directly over these venomous vipers.

To investigate whether or not puff adders used chemical camouflage, a research team, led by Wits post-graduate student Ashadee Kay Miller, began training dogs and meerkats to see if they could scent-match and detect the scent of puff adders. Miller’s team trained these mammals to match a target smell to one of six smells in a lineup. During dog testing, the target scent could be of wild or captive puff adders or their shed skins, or of any of five active-hunting, rather than ambush-hunting, snake species. The meerkats were tested with one activehunting snake species or a captive puff adder as a target. The lineup of scent-filled jars (for dogs) or tubes (for meerkats) included the target snake species among blank controls and environmental controls, such as vegetation or clean terraria.

Dogs and meerkats had little trouble pinpointing snakes that actively hunt prey. Dogs succeeded more than eighty percent of the time, and the meerkat success rate was more than ninety-two percent. Live puff adders, however, fooled both. Neither species could sniff out puff adders against the controls with odds better than guessing, though dogs could locate puff adders’ shed skins. The researchers believe puff adders’ passive lifestyle—lying in wait for prey for weeks, while avoiding their own predators—and lower metabolism may contribute to the snakes producing fewer or harder-to-detect odorous chemicals, a phenomenon that may occur in other ambush-hunting species. (Proceedings of the Royal Society B)