Parasites are everywhere. Big, small, pernicious, harmless; basically every living thing has something else living on it or in it or because of it. There’s something inherently creepy about parasites. Anyone who has watched Planet Earth has seen the stunning images of insect bodies completely ravaged by Cordyceps fungus and urban legends about 20 pound tapeworms abound on the internet. Even harmless parasites like bot flies (tropical flies whose larvae develop in mosquito bites in mammalian skin) which do not cause disease can definitely cause the willies. For some reason, people do not like the idea that something else is using us to make its living. (I am no exception to this.)
Despite their creep factor, parasites are also fascinating. Here are organisms that live part of their lives or maybe their entire lives in and on other organisms. There is no closer coexistence. My particular parasites of choice are the bat flies, flies that live on bats, feed on their blood, and breed on the walls of bat roosts. These flies are highly host specific, with certain species only found on one species of bat. The first time I caught a bat I remember watching these tiny brown specks scurrying all over the fur, with amazement and a little sympathetic skin crawling. I dutifully collected them and brought them back to the lab where my undergraduate research assistant and I identified them this summer. Amongst much head scratching over terms in our dichotomous keys (never let vertebrate and microbiologists do insect identification), we discovered something surprising; a few individuals of these parasitic flies were parasitized themselves!
I present to you the Laboulbeniales, an order of fungus that includes three genera that prey exclusively on bat flies. Like the bat flies themselves, these fungi are highly host specific and can range from virtually harmless, nourishing themselves solely from epidermal tissues, to fatal, invading the entire body cavity (Marshall 1981). There’s something elegant in the parallels between the parasites and their parasites; the range in severity, the close relationships between species, an exquisite partnering of parasitism on every level. And there’s a poetic justice to the fact that even creepy things have creepy things on them. Life will exploit every opportunity, however small, to make more life. Parasites are indeed everywhere.