Too Much, Too Soon?

A 2011 male bumblebee (over 500 grams) breeds 2 females.
Both females lay all slugs and the male is found belly up, dead.

This just happened to a good friend of mine last week.

Too much for the little guy to handle?

If proper breeding practices were observed and the animal was rested like they need to be then I wouldn't think that would be an issue. The Slugs could have been due to temperature issues with the female's being to hot. and the bee could have just had some kind of congenital problem that caused it to die..then again your friend could have bred the animal to death. No way to know for sure with out vet looking at the body.