Furcula (Collembola)

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The furcula is a tail-like appendage shaped like a fork, found on the fourth abdominal segment of springtails. Present in most species, it is used for jumping when the animal is threatened^[1]. While at rest, it is folded under the abdomen and held there by a structure called a "retinaculum", located on the third abdominal segment. When the retinaculum releases the furcula, it springs open and hits the substrate, propelling the springtail into the air. This mechanism is not used for locomotion, but only for escaping from predators.