So sorry!

I assume these are monarchs, and, if so, they probably had any of the several diseases monarchs get. There's a virus with a scientific name, but I just call it the black death - it sounds like what yours had, but it might have been something else.

Anyway, again, I'm sorry. :(

Sherry

So sorry. That is the unfortunate flip side of raising butterflies.

Believe it or not, depending on what the "black puddle" looked like can be a clue to what happened. Different things can happen. It could even be that it fell off the top (?) of the cage and the impact caused the death. Most likely it is some disease. There are a lot of different viruses that kill caterpillars. The worst is NPV. You might as well close up shop when that hits. The caterpillars literally "melt" into a puddle of goo. The caterpillar looks really shiny while this happens. Some viruses will turn the caterpillars iridescent before death. A bacterial infection typically will take longer and some may leak, some may not.

When you say you had to euthanize two, do you mean pupae or adults? Why did you euthanize them? If you have OE, another lovely infection caused by a protozoa, that causes failed pupation, then chances are all of your caterpillars are infected at a heavy rate. Some may make it, some not, but all of them regardless should be euthanized or at a minimum, the adults should be checked for OE spores (I think there is a FAQ on this).

For all diseases, a strong solution of bleach and water (I can't remember the rate, 1:10, I think) should be used to clean out all your rearing supplies.

Don't get discouraged. We all have failures of the worst kind. I had a lovely sphinx moth caterpillar that had just pupated when my husband knocked the container off the table killing the pupa. I was devastated. Especially since my daughter kept saying "I can't wait to see the moth that comes out next spring". Luckily she forgot about it by then but I will always remember it :(.

We should probably start a "disaster" post.

Good luck,
Elisabeth

Thanks Elisbeth and Sherry, it does look like he fell as the silk was frayed and there is also a black spot on the netting where it looks like he hit first before hitting the bottom. He didn't turn black, he still had the beautiful monarch cat colors, but he was really mushy when I picked him up for disposal.
I euthanised the little ones because a couple of days after moutling they simply quit eating and one check showed them simply writhing around as if in great pain... it was not a pretty sight, they were only in the 3rd instar.