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Join date : 2014-02-24
By Rob Dunn
They hide in your bed and breed on your face. They're smaller than the period at the end of this sentence. Several years ago I made a bet about face mites, animals that live in hair follicles. They are so small that a dozen of them could dance on the head of a pin. They are more likely, though, to dance on your face, which they do at night when they mate, before crawling back into your follicles by day to eat. In those caves mother mites give birth to a few relatively large mite-shaped eggs.
The eggs hatch, and then, like all mites, the babies go through moults in which they shed their external skeleton and emerge slightly larger. Once they're full size, their entire adult life lasts only a few weeks. Death comes at the precise moment when the mites, lacking an anus, fill up with faeces, die, and decompose on your head.
Currently two species of face mites are known; at least one of them appears to be present on all adult humans. My bet was that even a modest sampling of adults would turn up more species of these mites, ones that are totally new to science.
Mites also live in dust, where they have found unwelcome fame by eating the bits of dead skin that trail behind us everyplace we go. Our shadows of shed life sustain multitudes.
Just how many species of mites exist in the world today is not well understood. Probably at least a million, no one knows enough to say with confidence, nor will anyone know for decades. Museum collections are filled with mite species no one has yet had a chance to study.
Another reason for my bet: Mites are specialists that occupy every conceivable niche, including the trachea of bees, the shafts of feathers, the anuses of turtles, the stink glands of bugs, the digestive systems of sea urchins, the lungs of snakes, the fat of pigeons, the eyeballs of fruit bats, the fur around vampire bat penises. Living in these habitats necessitates special hairs, chemicals, foot pads, mouthparts, and tricks. It also requires a way to get from one patch of good habitat to the next.
Yet the marvels of mite transport pale in comparison with the idiosyncrasies of mite reproduction. Some clone themselves. Others eat their mothers. Others mate with their sisters while still inside their mothers and then, during birth, kill their mothers. In the nostrils of hummingbirds and the ears of moths lurk Greek tragedies of small, strange lives.
The habitats that offer mites the most advantages are bodies, whether of mammals, birds, insects, or any other creature larger than a mite. Bodies are the buffet bus of life, providing food and transportation. Mites that live on bodies are specially adapted to hold fast to their host, even when it runs, swims, or flies.
Most bird species host more than one specialized mite found nowhere else. One species of parakeet has 25 different species of mites living on its body and in its feathers, each in a different microhabitat. Rabbits host several species of mites, mice as many as six. Even seals have their own mites. Given such diversity and specialization, it's easy to imagine that a roomful of people (think of all the habitats!) would be fertile ground for discovering mites—and for making good on my bet. For a long time this was just a conversation starter at slow parties. But recently some collaborators and I gathered a group of folks and asked them to sample their own skin. After some swabbing, poking, and DNA sequencing, we found mites on every adult we sampled, including one species new to science that seems to live mainly on people of Asian descent.
How did mite systematics—scientists who name new species—respond? A few were excited; the rest shrugged. They knew that my bet for mite diversity was an easy one, a fact of life they witness every time they examine a scoop of soil, peer into moss, or swab a friend. In fact, one need look no farther than the mites pictured in this article, most of which are unnamed species. In all likelihood they will long remain that way, mysteries in plain view, like most of life.