Slow-mo dragonfly nymph labium (mask) in action. The actual strike only takes a fraction of a second. The labium is hydraulically activated by drawing in water, sealing the anal vent, and compressing the abdominal muscles. If the same action is performed with the anus open, the nymph will instead shoot forward on jet-propulsion, which it can use to escape predators or rapidly close in on prey.

Slow-mo dragonfly nymph labium (mask) in action. The actual strike only takes a fraction of a second. The labium is hydraulically activated by drawing in water, sealing the anal vent, and compressing the abdominal muscles. If the same action is performed with the anus open, the nymph will instead shoot forward on jet-propulsion, which it can use to escape predators or rapidly close in on prey.