Snaps of a tiny amphipod push the boundary of ultrafast, repeatable movement

Surprisingly, the fastest motions are not produced by large animals or robots. Rather, small organisms or structures, including cnidarian stinging cells, fungal shooting spores, and mandible strikes of ants, termites, and spiders hold the world acceleration records. These diverse systems share common features: they rapidly convert potential energy - stored in deformed material or fluid - into kinetic energy when a latch is released. However, the fastest and smallest known movements often cannot be used multiple times, because mechanical components are broken or ejected. Furthermore, some of these systems must overcome the added challenge of moving in water, where high density and viscosity constrain acceleration at small sizes. Here we report the kinematics of repeatable, ultrafast snaps by tiny marine amphipods (Dulichiella cf. appendiculata). Males use their enlarged major claw, which exceeds 30% of body mass, to snap a 1 mm-long dactyl with a diameter equivalent to a human hair (184 ...