Heather Proctor

This hair-raising feather mite is a vacuum cleaner for birds

Some things can’t be unseen. One is the final meal of a feather mite, a bloodsucking parasite that lives in the hollow quills, downy tufts, and outer layers of bird feathers. Or so scientists thought. Now, researchers have realized these tiny arachnids aren’t parasites after all, but may be beneficial cleaners that vacuum fungi and bacteria off bird feathers.

More than 2500 species of feather mites live in and on the feathers of almost every type of bird. Some of them—those that nest in the contour feathers that form the outer covering of a bird’s body—are thought to be so harmful that pet owners, zookeepers, and veterinarians try to remove them using special sprays or dusts.  

To better understand these mites, scientists analyzed their diets, looking inside the guts of 1300 from 190 species of bird. Instead of finding blood and skin, they found fungi and bacteria, which grow on bird feathers and can cause illness and feather loss, they report online in Molecular Ecology. They also spotted some plant matter and traces of gland oil that birds use for preening. To double check their findings, scientists isolated the DNA of the gut contents from 1833 mites. They found more of the same: lots of fungi and bacteria.

So instead of a parasitic relationship, feather mites and birds may have a mutualistic relationship where the birds provide the mites with food in exchange for cleaner feathers. The findings, scientists say, mean they may need to reevaluate their assumptions about the humble feather mite.