Normally when I have deaths in cats from general illnesses they turn a brownish color (no stench) and remain soft but firmish to the touch. If they are infected with fly parasites, the parasite emerge within an 1-24 hours after death of the caterpillar.
I had a small grouping of cats I collected at my house on August 16. This particular group soon showed signs of illness and eventually some cats died. Those that died... some turned that normal brownish color, but 2 cats (3rd instar) essentially became black liquid contained within a thin skin .. you could see the liquid jiggle within the skin of the cat if you moved the cup around and if it leaked out... stunk - definitely not the normal illness related deaths I get. The remaining cats from that group "recovered" and went on to pupate. The next odd thing I noticed was.. one chrysalis started turning black within an hour of finishing while 4 others turned black within 24-36 hours. The rest of the chrysalis were fine and the butterflies emerged today perfectly healthy (except for 1 whose wings are crinkled a bit because she lost her grip and fell to the bottom of the rearing container before the wings were fully dry). Of the chrysalis that turned black I kept them to observe thinking maybe a wasp infestation may have been the cause, but since the others emerged ok today I went to throw out the black ones. One of them broke open and this foul smelling liquid poured out and it stunk up the place like you would not believe.. ugh.
The cats I collected 2 days before and the group I collected 3 days after the sick group I collected... perfectly fine. Not sure why just one group would be sick but the others not. you would think that it would have shown up in at least the latter group that was collected if not the earlier group. The patch at my house has been dry.. no wetness or anything in the past couple of weeks.
ah... yes... definitely viral caused.. this explains exactly what this group had.http://www.teachingwithmonarchs.com/disease.html
Polyhedrosis Virus – “Melt”
This disease is also known as ‘melt’. Caterpillars and chrysalises with melt literally melt. The caterpillar turns into liquid which drips and splashes across leaves to be eaten by other caterpillars. Each caterpillar which ‘melts’ contains literally a billion virus particles. When a caterpillar eats these particles, it will ‘get’ the disease. The stench of a ‘melted’ caterpillar is horrible.
Nuclear polyhedrosis virus is characterized by a caterpillar dying and hanging by its middle legs. C polyhedrosis virus is characterized by a caterpillar dying and hanging by its rear legs (prolegs).
Six hours of full sunlight will kill the virus particles. Remember, however, that the underside of leaves or plants is not exposed to six hours of direct sunlight.
This disease is so effective as a caterpillar killer that pesticide companies create sprays to use in gardens, fields, or forests to control undesirable caterpillars.
Polyhedrosis virus occurs as CPV cytoplasmic polyhedrosis virus or as NPV nuclear polyhedrosis virus.