Parasitoids* are a frequent tragedy when you raise caterpillars. A perfectly normal looking caterpillar (like this Carolina Sphinx/Tobacco Hornworm caterpillar) can actually be full of eggs/larvae of parasitic flies and wasps.
I was given this Tobacco Hornworm as a gift, and by the time I got my hands on him he was prepupal and ready to dig a hole, make a subterranean dirt cocoon, and pupate. This was my first time with a sphinx moth caterpillar, and I gave him some dirt (rather than paper towels), because I didn’t know any better and wanted to replicate his natural environment. After a while, I wanted to find the pupa so I could keep a closer eye on it and watch the moth come out… but when I dug in the dirt, I could not find anything. Oh well.
Then one day, I started noticing these flies in the container. How did they get in there?! So I went outside with the container, let the fly out, went back inside. The container kept filling with flies. I saw them crawl out of the dirt, with their wings all shriveled (just like butterflies and moths, flies come out of their pupa with wings that need to be inflated!). Then I realized they were parasitoids–these are Tachinid flies, which commonly parasitize caterpillars. The eggs/larvae will hang out in the caterpillar until it pupates, and then they go to town, eat the baby from the inside out, and then they pupate inside the moth pupa, and emerge as adults. I was sad to not have a beautiful moth, but relationships between caterpillars and moth eggs and their parasitoids are under-documented, so it’s always interesting to see what happens.
*Parasitoids are organisms which live off another organism, and ultimately cause the death of the host in the course of their development. Parasites, in contrast, rely on the continued life of the host for their development. One example of a parasite is the botfly, which lives in the skin tissue of their hosts as a larva, then emerge to pupate outside of the host. If the host dies, the parasite dies.
Photos from June & July 2017 / Posted June 20, 2018