I recently brought home two Eastern Black Swallowtail caterpillars on some fennel that I purchased at the nursery. Shortly after setting these plants (and some parsley, rue and dill) on my patio table, I had eggs on them.

After my experience with Monarch caterpillars disappearing, never to be seen again, I started bringing these in the house to rear as well.

Both of the original cats seemed happy and healthy. The big one pupated successfully, and eclosed a few days ago. The smaller one seemed to be ready to pupate (it had started wandering) but I found that it had fallen off the plant and was just writhing around in the bottom of the container. I tried getting it to grasp a stem I offered, but it could never grasp the stem. It never did recover and was my first swallowtail fatality.

There have also been several others that died at various stages. Some were so little I could barely see them, and others had molted a few times before they died, after writhing around on the bottom of the container.

One of them actually strung itself up on the top of the critter carrier, but as soon as it started to pupate, it stopped. The skin split and I could see part of the chrysalis forming, and it stopped as soon as it started. Thinking that for some reason it was taking longer than normal, I left it alone, but it was very clearly dead the next day.

I'm more familiar with what types of things get to the Monarchs. I hate tachinid fly larvae and caterpillar eating wasps), but don't know what types of things cause the premature death of Eastern Black Swallowtail cats that don't seem to be parasitized. Is it possible that some type of parasite (that I don't see visible evidence of) is the cause of their deaths?