Water Boatman

Corixa punctata — the water boatman — is one of about 600 species in family Corixidae (the water boatmen — small aquatic true bugs that swim in pond and lake habitats worldwide). The species is widespread across temperate Europe and Eurasia, with closely-related Corixidae species across all temperate and subtropical regions worldwide (Sigara species and many others in NA, Europe, Asia, Australia). Adults are 8-10 mm long, with the species' diagnostic features: oval streamlined body adapted for swimming, dark grayish-brown coloration with fine darker mottled pattern, FRINGED HIND LEGS adapted as oar-like SWIMMING APPENDAGES (the source of the 'boatman' common name — the rowing motion of the hind legs when the bug swims looks exactly like a boatman rowing a boat), and short antennae adapted for the aquatic lifestyle. Water boatmen carry a layer of AIR ON THE BODY SURFACE (especially under the wing-covers and on the underside of the abdomen — held in place by hydrophobic body hairs) that serves as their oxygen supply during underwater excursions. The species is famous for the EXTRAORDINARY LOUDNESS of male mating calls. Male water boatmen produce STRIDULATION CALLS during mating that have been measured at 99 DECIBELS UNDERWATER (Sueur, Mackie, & Windmill 2011, PLOS ONE — recorded from European water boatman populations) — one of the LOUDEST ANIMALS ON EARTH SCALED TO BODY SIZE. The call is produced by RUBBING THE MALE'S PENIS AGAINST RIDGES ON THE ABDOMEN — a dramatically unusual form of stridulation (most insects stridulate by rubbing wings or legs together; water boatmen stridulate genitalia-against-abdomen). The call is so loud that human listeners standing on the bank of a pond can hear it FROM ABOVE THE WATER through the air-water interface (most underwater sounds are reflected by the water surface and are inaudible to listeners on land — the water boatman's call is loud enough to penetrate the air-water boundary). The biological function: the calls attract females to mating opportunities; the EXTREME LOUDNESS may reflect intense male-male competition (loudest male wins) or selection for calls that effectively transmit through water. The species and family are featured in essentially every modern textbook discussion of bioacoustics and underwater communication. Water boatmen feed primarily on algae and detritus (most aquatic Hemiptera are predators — water boatmen are unusual in being primarily herbivorous), making them significant beneficial aquatic decomposers and primary consumers in pond and lake ecosystems. The species is harmless to humans (no bite, no sting) and is one of the most-photographed aquatic arthropods in macro nature photography.