When one thinks of moths and their caterpillars, the first image that comes to mind is not of a killer that sucks its victims dry. Indeed, the majority of Lepidoptera are herbivores or detritivores. Some species occasionally resort to cannibalism or scavenging dead or dying insects when starving, but strictly carnivorous caterpillars are few and far between. The ones that exist, however, are pretty striking. Probably the most well-known and exciting are the Hawaiian species of the genus Eupithecia, small inchworms that are sit-and-wait predators of fruit flies. Videos such as this one abound on the internet, and it’s hard not to be impressed by their hunting prowess. Hawaii also hosts the predatory Hyposmocoma pupumoehewa (literally, ‘snail’s nightmare’), which ties down snails with silk, forces its way into the snails’ shells, and eats them. In the continental U.S, the predaceous Lepidoptera are not quite as cinematic, but equally fascinating.
There is a nice article on BugGuide that highlights the meat-eating moths of north america. One charismatic butterfly, the Harvester (Feniseca tarquinius) of the eastern U.S, feeds on wooly aphids as a caterpillar. The larva hangs out in the aphid colonies and munches its way through aphid after aphid. These colonies are usually attended by ants, who feed on the honeydew produced by the aphids and in theory are supposed to protect the aphids from predators – obviously they fail to do their job when Feniseca is involved. I first heard about this insect when I was in elementary school and I was told of an aphid colony in Holden, ME, where the Harvester was reported to frequent, but I never found it there. Years passed before I finally found a single adult sitting on a building on Cornell’s campus in Ithaca, NY. I have yet to see the caterpillar…
But among all these strange lepidopterans, one group stands out. The family Epipyropidae, with only 32 species worldwide, is fully parasitic on true bugs, mostly planthoppers but with at least one species, Epipomponia nawai, parasitizing large cicadas (see here for a fantastic photo of this). In the U.S. we have but one species, Fulgoraecia exigua, usually called the planthopper parasite moth. It ranges from southern NY to FL, west to CA, and has been found parasitizing many different planthopper species. The eggs are laid on plants, and the first instar caterpillars locate and attach to a planthopper, feeding on its bodily fluids for the rest of its days. The moth is a drab gray triangle that sometimes arrives at lights.
I have run across this odd animal on two occasions. In Maryland (2014), I came across several Fulgoraecia cocoons, which are immediately recognizable because they look like the Sydney Opera House (seriously!). I wanted to collect one to rear out the moth, but I feared I’d destroy the cocoons if I tried to detach them from the substrate, so I left them alone. Last fall (2017), I was beating shrubbery in Lebanon county, PA, when I noticed a planthopper Metcalfa pruinosa in my net that looked a little woozy. Upon closer inspectionI found a Fulgoraecia larva attached to the hopper’s abdomen! Unfortunately by the time I got around to photographing it, the caterpillar had already dropped off the (now deceased) planthopper and spun its cocoon, so I was unable to photograph the parasitic behavior. Two weeks later, the adult moth emerged and I was finally able to at least get a shot of that life stage. Hopefully someday I’ll be lucky enough to photograph the caterpillar parasitizing a planthopper.