Monarch Caterpillar Metamorphosis and Tachinid Fly Parasites

Monarch Bodysnatchers
Hello, Bugman,
I recently placed 2 large monarch caterpillars in an terrarium with some milkweed, so I could watch them go through metamorphosis. All was well… at first. One morning, I found one of the caterpillars hanging from under a branch, as though ready to pupate, but it was dead, shriveled, and and clear strands hanging from it. There were two small, yellow maggots in the tank, as well as a red pupa. After a bit of searching, I found this site /research/PNE/creasey.aspx . Apparently, an introduced tachinid fly, Lespesia archippivora, was brought over to control cutworms, but attacks non-target species like monarchs as well. Fortunately, the other caterpillar seems to have dodged the bullet, and has formed a lovely chrysalis. Regards,

Monarch Caterpillar Monarch Chrysalis

Hi Emily,
Thank you for your wonderful letter, excellent photos, precise documentation, and technical research. Though we approve of biological control methods over pesticides, we always question the introduction of biological agents before the total ramifications of the actions are made apparent.

Parasitized Monarch Caterpillar Tachinid Fly larvae and pupa

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