strange beehaviour?

pardon the pun .. i've noticed all these bumblebees acting really weird this week, they seem to be eating flies, i didn't think they do that, and a lot of them have been dropping to the ground from exhaustion and starvation, saw a few dead ones on the ground, they've been ignoring all the flowers all around them and eating baby flies in stead.. they seem to be anyway, at first i thought they were looking for shelter from the rain the other day, inside curled up leaves, but there were even more doing it yesterday and more still today when it's been bright and sunny .. maybe that's what the first few were doing, just trying to get out of the rain, and that's when they learned how delicious meat is, and now they've taught other bees to like it as well.. or maybe some GM plant's pollen's messed with their heads or something.. or maybe it's always been happening and i've just never noticed.. has anybody else seen anything like this?