In the London study that first examined raccoon food-washing habits, the 10 animals "washed" meat more often than plants, but didn't rinse off dirty earthworms [source: Lyall-Watson]. Even if no water was available, the captive raccoons would move their forepaws in the same way they would if they were actually dousing the food item. To the researchers, this behavior indicated that the raccoons weren't intentionally cleaning their food before eating.
But that doesn't mean it's a useless gesture — removing dirt from their meals is merely a beneficial byproduct of the action. Initially, scientists conjectured that raccoons lacked saliva glands and needed to add moisture, making it easier for them to eat [source: Zeveloff]. Instead, study results have indicated that the behavior enhances the tactile experience involved with eating.
As we mentioned, raccoons have highly dexterous forepaws that resemble hands. Raccoons actually have the same nerve grouping on the hairless parts of their forepaws as primates have, including humans, making them very sensitive to touch. Like primates, they have similar slowly adapting nerves in those hairless, or glabrous, patches [source: Rasmusson and Turnbull]. Slowly adapting nerves are responsive for both moving and stationary skin displacement, communicating to the brain, via the central nervous system, information about the weight, size, texture and temperature of whatever's come into contact with the forepaws. There are also nerves attached to underfur and longer guard hairs.
In a study examining the slowly adapting nerves in the forepaws of 136 raccoons, researchers found that wetting the skin increases the nerve responsiveness [source: Rasmusson and Turnbull]. Think about what happens when you look through a pair of sunglasses and then quickly take them off. When you remove them, your optical nerve responsiveness will likely increase because more light is flooding into your retinas to illuminate what you're looking at. Likewise, when raccoons perform their dunking ritual, the water on their paws could excite the nerves in their forepaws. That, in turn, gives them a more vivid tactile experience and provides precise information about what they're about to eat. This is a beneficial trait since the raccoon's vision isn't its keenest sense.
Like primates, raccoons employ a combination of sight and touch to reach out and grasp an object (unless, of course, they're reaching into murky water). However, raccoons often use both hands, rather than one, to grasp, and they exhibit little independent movement of their digits [source: Pubols, Pubols and Munger].
One interesting difference in tactile sense between raccoons and primates is the raccoon's lack of papillary ridges. The ridges are microstructures in our skin that help us detect friction and create our fingerprints. In the hairless areas of human skin, namely our palms and soles, the ridges are packed with Meissner corpuscles. These individual living cells serve as specialized mechanoreceptors, responding to sensations like pressure or tension. With all of these factors combined, a study observing raccoons' eating behavior concluded that while their dexterity is specialized, it isn't as much of an anomaly as the washing behavior implied at first blush [source: Pubols, Pubols and Munger].
From a public relations standpoint, that probably isn't such a good thing for the raccoon. Previously, the rabies-carrying, food-stealing animal had the distinction of at least washing its food. Now, it looks like those sticky fingers could use a thorough rinsing.
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More Great Links
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Last editorial update on Sep 17, 2018 04:00:35 pm.