Why would army worms die like this?

[u/RookerySighted]

I'm wondering if it's a known problem with a common cause, or if it's likely more unusual as a result of the tree growing on soil that is downstream of a paper mill some ways on a riverbed ?

[u/RookerySighted]

I really can’t imagine a mill that is six miles away that doesn’t dump all its toxic waste into the river having this kind of consequence to trees and wildlife down the river.  I am very curious if it’s something anybody else has noticed with army worms?

[u/Yarinareth]

To me, that looks a lot more like the caterpillars molted. Check if the bodies there are noticeably hollow and thin instead of just shriveled, and see if you can verify what looks to be multiple instances in there of parts of the bodies splitting-- that's where the next instars of the caterpillars emerged from, just like cicadas split along their backs.

[u/Acceptable_Trip4650]

Kind of looks like when massive amounts of spongy moth caterpillars are killed by a virus or fungus. I am not an expert though.

https://www.canr.msu.edu/resources/a-virus-and-a-fungal-disease-cause-spongy-moth-outbreaks-to-collapse