The Thick-headed Fly is so named not because they're particularly stupid, but because their heads are larger than their thoraxes. They seem fairly docile, but don't be fooled - their method of egg incubation can only be described as, er, hit and run.

Females will wait on flowers for bees to come nearby, using themselves as bait. When the bee attacks, the Fly strikes back and injects a single egg into its abdominal section. The larva hatches and feeds on the bee's blood until it's a bit bigger - then, it starts eating its host. The bee dies, often in flight, and the larva pupates within its corpse over winter.