Last fall, in the midst of my first monarch experience, I came home to a very depressing sight. My first chrysalis, which I had named Trigglet, had turned a muddy brown and had a white string hanging off of it. I already had my suspicions that Trigglet had some kind of problem. Since I’d never raised monarchs before, I would compare Trigglet’s chrysalis each day to the pictures of healthy monarch chrysalides on the web. Here’s how Trigglet compared to one of my later chrysalides:
The slight mottling on Trigglet became a muddy orangish-brown color as the days wore on:
(The white threads that I referenced in the introduction are not the threads you see above. Rather, that is tooth floss that I used to hang each chrysalis up on a wire for more convenient gawking.) Here’s what Trigglet looked like the day I knew my butterfly would not appear:
The tread dangling of the bottom screams: this monarch is toast! I sat down with my copy of “Milkweed, Monarch and More” (MMM) to figure out what had happened. Turns out, my monarch caterpillar was the victim of a parasitoid called the tachinid fly. I sat fascinated by the story of this insect. A parasite is a creature that lives in or on another host organism and derives nutrients at the expense of its host. A parasite doesn’t normally kill its host, but it does reduce the host’s fitness and fertility. A parasitoid, on the other hand, kills its host. The tachinid fly finds an egg or caterpillar to lay its own egg upon. From the MMM book:
“The tachinid larvae burrow into the caterpillars’ bodies and consume them from within. They eat non-essential tissues first so that the caterpillars live long enough for them to complete their development. Telltale threads hanging from a limp caterpillar body or chrysalis are a sign that tachinid larvae have left their host to pupate on the ground.”
I jumped out of my seat. This information meant that I had a fly larva – a MAGGOT chrysalis – on my porch! I hopped over to the crime scene and looked at the porch tile under Trigglet. Here’s what I found:
One intact tachinid chrysalis and one which I must have squashed when I first checked my monarch chrysalis. Since these parasitoids had already killed Trigglet, I decided to do an autopsy to see what it looked like inside my little monarch chrysalis:
This is a tachinid fly larva that didn’t get the chance to pupate. Until I started writing this entry, I didn’t know what caused the little white threads that hang from the monarch chrysalis. After finding this video, I can see that it’s dried goo attached to the pupating maggot.
To reduce the chances of having your monarch caterpillars fall prey to predators and parasitoids bring them indoors to raise as soon as you discover them on your milkweed. And always wash the milkweed you take out of the garden to feed to your caterpillars.
Sadly, a second monarch chrysalis later fell victim to the same fate. I had to remind myself that the tachinid fly does a service in the garden when it takes out pest insects. I just wish it hadn’t found my little monarch caterpillars. The experience made me second guess my bright idea of naming my babies before they hatched. I posted the picture below on Facebook with the following note:
Remember a couple of months ago when I discovered that a tachinid fly had parasitized the monarch chrysalis that I had named after my (somewhat) favorite niece Hatbox (Hadley)? Well, I put that chrysalis in a mason jar along with the fly chrysalides. A couple of days ago, I noticed that one of the flies had hatched (it’s legs-up in the picture below).
Anyway, congratulations Hats — your namesake is a dead fly.