[PepperdineG]

It could be something like what happens with honey bees in chimneys. Honey bees think they've found a great hollow tree home with it even smelling like a tree due to creosote, but creosote levels are so high that it makes sick bee colonies. With bumblebees it might be something where bees are naturally attracted to smell thinking it's a good thing without being able to recognize there can be too much of a good thing, so will make them sick.

[kbelder]

Like humans and sugar.

[beretguy]

Or like humans and beer.