Dec. 16, 2007 -- Most snakes give off a subtle odor that's akin to gamey fried chicken, but it is a useful smell to rock squirrels and California ground squirrels, which chew shed rattlesnake skins and then lick their fur with their snake-scented spit, according to a new study.
The rather indelicate ritual likely helps squirrels fool their rattlesnake arch nemeses. The discovery may represent the first documented instance of a vertebrate self-applying a chemical from a foreign source in order to defend itself against predators.
The squirrels don't even seem to like the taste or texture of rattlesnake skin.
"As far as we can tell, they do not consume the skin and at times we would see pieces of the skin stuck onto the squirrels' fur after they licked their bodies," lead author Barbara Clucas told Discovery News.
Clucas, a scientist in the Animal Behavior Graduate Group at the University of California at Davis, and her colleagues witnessed the behavior while studying squirrels and rattlesnakes at Lake Solano County Park in California and at Caballo Lake State Park, New Mexico.
Similar to how a person might always apply scent onto certain select areas, the squirrels typically twist to the side, lick their flanks and then grab their tail with their forepaws and lick the tail from its base to its tip. Like a big powder puff, the tail might help to waft the rattlesnake scent into the air.
The findings have been accepted for publication in the journal Animal Behavior.
Clucas and her team next tested to see if the scent served to deter other squirrels, parasites or predators.
The eau de snake, at least when it was on the squirrels, didn't seem to bother the other squirrels at all. Next, the researchers anaesthetized several squirrels and counted the fleas on their bodies for a period of one minute. They determined that the rattlesnake-infused spit did not change squirrel flea loads.
Finally, they predicted that if juveniles and females applied more of the snake scent it would indicate the behavior serves to ward off rattlesnakes. That's because juveniles are more vulnerable to snake attacks, and their mothers actively protect them from snakes, putting them at greater risk of attack too.
Sure enough, juveniles and females did engage in the scent application procedure more, indicating that the smell does help to deter snakes, and perhaps other predators that are also scared of snakes.
It can be hard to fool a snake, Clucas pointed out, since they possess a keen visual system and special pit organs that essentially enable them to see body heat.
"However, ground squirrels spend quite a lot of time underground in their burrows," she said. "So applying snake scent may benefit squirrels that are asleep (underground), unaware of a snake investigating their burrow."
Daniel Blumstein, associate professor in the Department of Ecology & Evolutionary Biology at the University of California at Los Angeles, commented that "the squirrels essentially 'cross dress' and mask their own scent with that of snakes."
"This is neat because it illustrates yet another way that predators and the risk of predation select for adaptations to reduce the risk of predation and it tells us to look widely for those adaptations," he told Discovery News.
The find additionally places squirrels on the list of other creatures that apply stinky foreign substances to their bodies. These include hedgehogs applying toad skin scent, rats wearing weasel smells, birds applying millipedes to their feathers and primates, including humans, that apply all sorts of stink in hopes of avoiding bug bites.
Related Links:
Jennifer Viegas' blog: Born Animal
Squirrel Wildlife Rehabilitation
Interesting Facts About Squirrels