A grisly scene in Kibale forest, Uganda:
I found this long-dead cadaver stuck to a tree trunk at about waist height. The body must have been there for months or even years, judging from the moss growing across the cuticle.
Why is this puzzling? Rainforests are intensely competitive environments, and free protein does not stick around for long. So why would a perfectly good ant go uneaten?
My suspicion is fungus. If the ant was killed by a Cordyceps-type organism, the tasty innards would long have been consumed by the parasite. Still, that’s just a guess.

I agree. you can see an infected worker on http://www.webarchive.org.uk/wayback/archive/20101217234724/http://antbase.org/ants/africa/polyrhachis/polyrhachis_militaris/polyrhachis_militaris.htm
I remain hopeful of getting the getting the site hosted by Oxford UMNH after AMNH killed it this time last year.
I’m not sure about your proposed time for the presence of this ant skeleton. I have seen plastic flagging, used for trail markers in lowland Ecuador, that began to sport spots of epiphytic lichens and algae in less than two weeks. The appearance of this ant skeleton reminds me of that. Also note that an exoskeleton eviscerated by the fungal parasite is more chitin than protein, the former also a nitrogen source but much harder to digest.
Perhaps that’s my temperate bias showing, James.
What did the autopsy show?