Tachinid Flies and Monarch Butterflies

Tachinid flies are small flies that look like hairy houseflies. There are something like 1300 varieties in North America apparently. They are generally considered to be beneficial in that they help control garden and horticultural pests. If you were an organic gardener you would welcome these flies to your farm or yard.

Of course, those of us who like to play God and favor one species over another are on the flip-side of the coin and consider tachinid flies mortal enemies because they prey on our precious monarch caterpillars!

Depending on the variety of tachinid fly, they either lay their eggs on the back of the head of the caterpillar or inject the eggs into the caterpillar. In the case of those eggs that are laid on the the outside of the caterpillar, the larvae burrow into the caterpillar once they emerge. So no matter what, the larvae end up inside the caterpillar enjoying the ride while feasting on our precious ones.

The larvae do not actually kill the caterpillar as they need to allow it to pupate (form a chrysalis) from which the tachinid fly larvae will emerge on mucous-like threads that reach to the ground. "3-2-1 Bungee!" (If you've even been or seen bungee-jumpers you'll get that last reference). Once the fly larvae hit the dirt, they themselves pupate before emerging as flies.

Photo by Nigel Jones at Flickr
Used under Creative Commons License

Well I kind-of sort-of figured I have tachinid flies in my garden. For a start they are nectar-eating flies and I have nectar plants for my monarchs. And I have seen flies that look like this in the photo by Nigel Jones often enough.

Well this morning I was checking some chrysalises that I have sequestered in individual jars so I can test them for O.E. for the Monarch Health research project being conducted by the University of Georgia, and I came across one of the jars with the tell-tale strings hanging down off the chrysalis. Lifting the lid I saw two larvae wiggling on the bottom of the jar.

Of course I grabbed my trusty cell phone and recorded the following video of the action for all to "enjoy". Alien III!