Bumble bees are rather charming, buzzing from flower to flower with their furry black and yellow bodies. Depending on where you live, the bees you see might be escapees from a greenhouse or "bumble bee factory." They might even be descendants of stowaways on Viking ships. Thanks to humans, bumble bees are world travelers, spreading to countries that never hosted bumble bees before. For centuries these insects pollinated our crops. But are they pushing out native pollinators? Why are some species of bumble bees flourishing whereas others are floundering, to the point of possibly disappearing forever?