This Fly Torpedoes a Bindweed Bee's Nest

A “bee fly” looks a bit like a bee, but it’s a freeloader that takes advantage of a bindweed turret bee’s hard work. The bees dig underground nests and fill them with pollen they collect in the form of stylish “pollen pants.” As the bees are toiling on their nests, the flies drop their *own* eggs into them from the air. But the bees employ a tricky defense against the flies.