You are not alone. Your body is a collection of microbes, fungi, viruses … and even other animals. In fact, you aren’t even the only animal using your face. Right now, in the general vicinity of your nose, there are at least two species of microscopic mites living in your pores. You would expect scientists to know quite a lot about these animals (given that we share our faces with them), but we don’t.
Here is what we do know: Demodex mites are microscopic arachnids (relatives of spiders and ticks) that live in and on the skin of mammals – including humans. They have been found on every mammal species where we’ve looked for them, except the platypus and their odd, egg-laying relatives.
Genomics & Microbiology Lab Assistant Director Julie Urban and other scientists from the N.C. Museum of Natural Sciences, N.C. State and the California Academy of Sciences have just published a study in the journal PLOS ONE that uncovers some unknown truths regarding these little-known mites – all the while providing a glimpse into even bigger mysteries that have yet to be solved.
One of our most exciting discoveries is that these mites are living on everyone. Yes everyone (even you). This hasn’t always been obvious because it can be hard to find a microscopic mite living on one’s face. Traditional sampling methods (including scraping, or pulling a piece of tape off your face) only return mites on 10 percent to 25 percent of adults. The fact that mites are found at a much higher rate on cadavers (likely because the dead are easier to sample more extensively and intrusively) was a hint that they might be much more pervasive.
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As it turns out, you don’t have to actually see a mite to detect its presence. Dan Fergus, a mite molecular biologist working in Urban’s lab, discovered that mite DNA could be sequenced from face scrapings regardless of whether a mite could be found under the microscope. And mite DNA was sequenced from every adult we sampled. In other words, if you let us scrape your face, we’d find mite DNA on you. And where mite DNA is found, you’ll find mites.
One of the most intriguing (and unsolved) face mite mysteries is how humans acquired these beasties. Perhaps these mites are a model system of co-evolution. It’s possible that as every species of mammal evolved, so did their mites – each one particularly adapted to its changed environs. In such a case, we would expect that we acquired our mites from our ape ancestors, and that the two species of human mites would be more closely related to each other than to any other mite species.
However, we’ve learned that the two mite species on our faces – Demodex folliculorum and Demodex brevis – are actually not very close relatives to each other at all. In fact, brevis is more closely related to dog mites than to folliculorum, which shows us that humans have acquired each of these mite species in different ways.
If reading this made your face a little itchy, rest easy. In an evolutionary perspective, humans and Demodex are old, old friends. You are in good company. And so are your mites.