I've been watching the caterpillars I discovered Sunday on my Butterfly weed. Slowly they are disappearing and I have so far found two dead ones. We do not use chemical pesticides/herbicides and only GreenBug (cedar oil) had been used on the cabbage well away from the BFweed.

I had a rather large one yesterday that is no longer on the plant it was feeding, so I am hoping it is pupating somewhere out of sight, but the others were small to medium size.

These BFweed were from the local nursery this spring, but the owner did them special for me. I asked him to use no chemicals whatsoever on them. He obliged and after a slow start they are growing beautifully and some even flowering.

Does anyone have any ideas? Parasite perhaps? As far as I know, the seeds were not treated. He lost the first batch from a fungus.

Thank you for any input.

I've heard that in the wild only about 2% make it to become butterflies. Maybe this will give you some info.
https://monarchbutterflygarden...
http://monarchparasites.uga.ed...

Thank you so much for the links. I did find two large healthy ones this morning in this patch, so that is encouraging. I hope they make it.

Predators which might have made off with some of your caterpillars include spiders, preying mantises, frogs, toads, snakes. If the cats have disappeared entirely I would suspect one of these. However, some predators like stink bugs and their ilk suck the insides out; the skin quickly shrivels and dries and may fall to the ground where it would be difficult to find.

Yes Chilly, there are about 10,000 things (a modest estimate) that eat larva. In addition to the above i would add wasps that chow down on caterpillars and/or inject them with parasites. Wasps are the primary predators of caterpillars in my garden and they range in size from 2" to almost microscopic. Also caterpillars can have parasites from birth passed down from the mother butterfly or picked up from the host plant or immediate environment. If caterpillars are bothered by predators on the host plant, they may wander away from time to time. Also, they will occasionally leave the host plant to molt, especially if bothered by various predators on their host. The caterpillars are especially vulnerable during molting. Take a look at your plants from time to time to discover what kinds of bugs are regularly hanging around and/or also populating the plants and you may get an idea of what is happening to the caterpillars.

Great links, Linda!