Puff adders in Africa are ambush foragers that rely on patience and stealth to catch prey, though their lying-in-wait strategy often puts the squat, venomous snakes at risk of being spotted and eaten themselves.
While they’ve evolved extremely effective visual camouflage, over a dozen of their predators are known to hunt using scent. But thanks to a form of chemical camouflage, puff adders are able to limit their detection, according to findings published in Proceedings of the Royal Society B earlier this month.
Ambush foraging typically requires long bouts of immobility followed by a rapid lunge or strike at passing prey. Many snakes are able to deal with the infrequent prey intake by shutting down their digestive machinery between large meals. Unlike active foragers, ambush foragers are a continuous source of odors.
A type of camouflage called chemical crypsis would provide an advantage – for avoiding detection by both their prey and predators – but this tactic isn’t well studied. Previous observations of puff adders (Bitis arietans) revealed that they go undetected by several scent-orientated mammals, and that they typically choose to stay motionless in response to approaching danger.
So, a team led by Ashadee Miller from the University of the Witwatersrand trained four dogs and five meerkats to see whether these scent-oriented predators could detect snakes using just olfaction. They tested for chemical crypsis in puff adders as well as five species of easily detectable, active foraging snakes. The dogs and meerkats were presented with cotton cloths scented with the smell of the various snakes in a line-up that included blank controls (washed, unscented cloths) and environmental controls (cloths scented with vegetation, for example).
The dogs and meerkats accurately, repeatedly, and unambiguously detected the scent of all the active foraging snakes but failed to detect puff adders – confirming chemical crypsis was an important part of the ambusher’s arsenal. This overlooked phenomenon is likely widespread among other ambushing species. The dogs were, however, able to locate the scent collected off the freshly shed skin of a captive puff adder, though the snakes typically defecate at the site of shedding before moving on.
This work provides the first evidence for chemical crypsis by a vertebrate organism as defense against scent-oriented predators. “Our study,” the team writes, “provides additional evidence for the existence of an ongoing chemically mediated arms race between predator and prey species.”
