If you're squeamish, you probably don't want to read about what's going on here.

This Hog Sphinx Moth caterpillar, seen here on Smartweed, has been parasitized by Cotesia congregata, a braconid wasp that lays its eggs in the caterpillar. (Many thanks to evanioidea for the species ID.) They are now pupating in the white cocoons hanging from its back. The caterpillar was still moving, but just barely.

There's no particular reason I should feel more sympathy for the caterpillar than for the wasp. In fact, sphinx moth caterpillars such as tobacco hornworm & tomato hornworm are agricultural pests, & such wasps would make good biological controls. (I wouldn't be surprised if they're used as such. In fact, this photo wasn't taken on a farm, but there are farm plots within a mile or so -- this is part of Cook College, Rutgers' ag school.) But it just seems like such a horrible death, eaten alive from the inside out. I'm a biologist & not particularly squeamish, but I find this photo both awfully cool and awfully disturbing.

If you're squeamish, you probably don't want to read about what's going on here.

This Hog Sphinx Moth caterpillar, seen here on Smartweed, has been parasitized by Cotesia congregata, a braconid wasp that lays its eggs in the caterpillar. (Many thanks to evanioidea for the species ID.) They are now pupating in the white cocoons hanging from its back. The caterpillar was still moving, but just barely.

There's no particular reason I should feel more sympathy for the caterpillar than for the wasp. In fact, sphinx moth caterpillars such as tobacco hornworm & tomato hornworm are agricultural pests, & such wasps would make good biological controls. (I wouldn't be surprised if they're used as such. In fact, this photo wasn't taken on a farm, but there are farm plots within a mile or so -- this is part of Cook College, Rutgers' ag school.) But it just seems like such a horrible death, eaten alive from the inside out. I'm a biologist & not particularly squeamish, but I find this photo both awfully cool and awfully disturbing.

Wasp obs at https://www.inaturalist.org/observations/505539. Caterpillar obs at https://www.inaturalist.org/observations/531855. More on the virus at https://en.wikipedia.org/wiki/Cotesia_congregata. The virus is encoded in the parasitoid's nuclear DNA and expressed in specialized cells in its oviduct so that virions are injected into the host along with the egg.