NEW ORLEANS, LOUISIANA—Whether on an African savanna or a feedlot in Texas, mammals are plagued by myriad insect pests: mosquitoes with malaria parasites, tsetse flies spreading African sleeping sickness, horseflies transmitting rinderpest. And in their defense, giraffes, zebras, cows, and the like depend on their tails to swish the insects away. Now, mechanical engineers have discovered just how good these rear-end fly swatters actually are. To find out, they filmed 19 videos of swishing tails from six species, analyzing how fast the tails moved and how their movements changed after insects landed. They discovered that these mammals put a lot of effort into shooing away would-be biters, swinging their tails three times faster than a gravity-driven pendulum, the team reports today at the annual meeting of the Society for Integrative and Comparative Biology. The tail works like a double pendulum in that it swishes from where it sticks out of the butt and then from another pivot point where the bone and skin part of the tail ends and the hair begins (see video above). Because of that second pivot, the tip can swing at a different speed or even direction than the rest of the tail. This flexibility enables the animal to interrupt its swishing and use both pivot points to take aim and powerfully swat the intruder before it has a chance to bite. Now that they know how the natural swatter works, the team says they might be able to one day build prosthetic tail tips for animals that lose theirs.