Hello! I have a question about something I saw a little while ago. I was watching some caterpillars on a milkweed plant, and I saw one that was completely dead but squishy. I though that maybe it was a shedding, but it seemed to be a whole caterpillar. Do you know what happened?
(Black one pictured next to healthy one)
Yes, it's definitely a dead caterpillar next to a healthy one. The one on the left has died of something that's known as black death. It's a bacterial infection that affects monarchs. I think there's a virus that causes similar symptoms as well. They will turn black, have runny poop, regurgitate their food, and then start to deflate and liquefy. It's contagious and as far as I know, always fatal. They can sometimes manage to pupate, but then their chrysalis will turn black and they'll never emerge :(