In the dark and moist understories of the subtropical forests of Shimoshima Island in Japan grow parasitic plants that feed on the roots of other plants. They are called Balanophora, and for over a century, the mechanism of their seed dispersal has remained a mystery.

A creature that burrows headfirst into flesh, driving sharp hooks into open wounds and feeding on their hosts? It sounds like the stuff of a horror movie. That’s the New World screwworm, a parasite that can kill livestock and occasionally infest humans. It was previously eradicated from North America, but has been moving northward again and was recently found in southern Mexico, setting off alarm bells for officials in the federal and Texas...