I've come across a problem in different seasons with Hyalophora caterpillars that begin to exude a blackish liquid from the mouth, languish, then expire.
This has occurred using different food plants, either sleeved on branches, or caged with a potted plant. It happens outdoors and indoors as well, there seems to
be no common thread, except the result, a dead and probably contagious caterpillar.
Sometimes it has killed every larva, even larva separated by what I would have thought a safe distance, other times it will take only one, I've seen it at the final instars,
and most recently the third instar, but that's as young as I've seen a caterpillar get this frustrating malady.
Perhaps this happens with other species, it's just that I have most of my rearing experience with the Hyalophora.
Any input would be appreciated, at least for now, this has only occurred with relatively common species, but losses are always a frustration.
kevin