l: Today on A Moment of Science--reindeer flies. Don: Flying reindeer?? Y: No, reindeer botflies, or reindeer nose bots. Reindeer and other large mammals are often plagued by botflies. Botflies are parasites that deposit larvae inside the noses of their hosts. The larvae burrow into the flesh of their nasal passages, causing pain, breathing trouble, and other serious problems. D: Whoa, that's horrible! Y: The deer think so too, and learn elaborate behaviors to avoid the flies. When  experienced deer see or hear a botfly, they'll sneeze to try to blow the fly away. Then they'll thrust their heads down to press their noses into the snow or a clump of grass, looking cautiously around to be sure the fly is gone before raising their heads.    But the flies have evolved sneakier and sneakier ways to get at their hosts. Two different species of botfly have evolved opposite attack strategies.  One species uses stealth. These flies are able to fly and hover silently. They approach deer slowly from behind, staying low to the ground. Then they position  themselves just below the deer's nose. From this "blind-spot" in front of the deer, a  fly can dart up and squirt a batch of larvae into the deer's nostril. D: That is sneaky! Y: Other botflies exploit the deer's natural curiosity. These flies buzz conspicuously and  land on a deer's hindquarters. When the deer turns to investigate the fly, it has to  stretch its neck out awkwardly. Deer in this position find it hard to evade a fly when  it nips in to deposit larvae; they can't move their noses quickly enough. D: Hmm. Maybe that's why Rudolph's nose is so red!