The Krill Drill

Antarctic krill, small shrimplike creatures, swim in dense schools of 20,000 or so animals per cubic yard. To avoid turbulence they adopt a staggered formation so that no krill swims directly in another’s wake. That obviously requires some kind of coordination. Konrad Wiese, a zoologist at the University of Hamburg, thinks he’s figured out how krill keep in touch: their tiny antennae pick up pressure waves from their neighbors. Wiese glued a tiny Lucite block to a krill to immobilize it, as shown here, and placed a small pressure sensor near the swimmerets--the bristle-covered legs that propel the animal. He detected four distinct signals: a low-frequency wave coming from the paddling swimmerets themselves and three higher-frequency signals from the bristles, which increase the surface area of the swimmerets by folding and unfolding as the krill swims. The low-frequency wave, Wiese thinks, tells each krill how fast the krill ahead is ...