Where Do Butterflies Go To Die?

The obvious answer is in the digestive tract of something that preys-upon butterflies.  Birds, omnivores that walk on four legs and other insects.  Which explains why it is rare that you find a dead butterfly laying around somewhere to be discovered by an observant individual. 

I think the best chance of finding a dead and unconsumed insect of any consequence is the garage or machine shed.  Once they fly-in they're trapped and quite likely to die.

Monarch butterflies feed on milkweed (their host plant) and as a consequence ingest and store milkweed toxins known as cardiac glycosides.  This makes the larvae and adult butterfly toxic to birds and other predators who have learned to avoid these weaponized butterflies.  

Which might just explain this situation. 

A dead monarch in the yard.  Pieces of it anyway.  I suppose there is a first time for everything...