When I ask Sara Weinstein about her favorite parasite, she laughs, and has a quick answer. “I think the flies that parasitize frogs are really interesting,” she says.

There are many species of them, including two known as toadflies. The females lay their eggs on frogs and toads—sometimes on their skins and occasionally in their nostrils. When the maggots hatch, they eat their way inward, and you can sometimes see them through the wounds that they open in their host’s flanks. Their appetites are usually fatal. Once their hosts have ribbited their last, the larvae fall away and turn into adults.

Many insects also get devoured alive by the larvae of parasitic wasps, flies, and more. But the