Water Scorpion

Nepa cinerea — the European water scorpion — is one of about 270 species in family Nepidae and one of the most extraordinary cases of convergent evolution in the insect world. Despite the common name and the visual resemblance to scorpions, water scorpions are NOT scorpions (which are arachnids in the order Scorpiones); they are true bugs (Hemiptera, the same order as bedbugs, cicadas, and assassin bugs) that have independently evolved a body shape and behavioral repertoire similar to scorpions through convergent selection on the freshwater ambush-predator niche. The body is flat, leaf-shaped, brown, and 18-22 mm long, often with twigs and algae attached to the body for camouflage. The front pair of legs are dramatically modified into raptorial pincers — anatomically and functionally analogous to the pincer pedipalps of true scorpions and to the raptorial forelegs of praying mantises (yet a third independent evolution of the same prey-capture body plan). The rear of the abdomen extends into a long thin siphon (the 'tail' — but not a stinger or weapon of any kind) that functions as a snorkel: the water scorpion holds the siphon at the water surface while resting submerged, drawing atmospheric air through the tube to a tracheal system for respiration. The species is a slow-moving ambush predator of small fish, tadpoles, mayfly nymphs, and other aquatic invertebrates — she sits motionless on submerged vegetation or pond bottom and grabs passing prey with the raptorial front legs. The bite is harmless to humans (no venom, no mechanical danger). The species is widespread across Europe and into central Asia in still and slow-moving freshwater habitat.