What good are ___ ?

Fill in the blank with the objectionable life form of your choice — mosquitoes, black flies, slugs, parasitic worms, unnamed things that are too squishy for words.

Although the question “Why are we here?” is much trumpeted as a human preoccupation, what most of us really want to know is “Why are they here?” And if “they” are nonhuman (the presence of other people remains a complete mystery), science is pretty good at coming up with answers.

All those bacteria that live in and on us, and outnumber our own cells? They help our digestion, fight off bad bacteria and keep us humble. Bats? They eat insects. And in the latest news, researchers have found that European hornets and paper wasps, which pack a sting nasty enough to make anyone question their reason for being, provide a cozy winter home in their guts for one of humanity’s most important microbiological buddies: yeast.

The yeast in question is Saccharomyces cerevisiae, sometimes called baker’s yeast, but particularly important in the making of wine, as well as beer and bread. I wasn’t even aware that yeast had a second home until I read about this research. But it does, and now we know where.