Water-boatman (Arctocorisa arguta) and Back-Swimmer (Anisops wakefieldi).
Both these insects have many things in common. They are true bugs; they live in still, freshwater areas especially ponds and stagnant pools throughout New Zealand; and their means of locomotion in water is by the rowing-like action of their hind pair of legs. The back-swimmer swims only on its back while the water-boatman propels itself dorsal side uppermost. Both are carnivorous and feed on insect and other animal life in the water. Mosquito larvae are an important part of their diet. The water-boatman can be distinguished by its body which is compressed dorso-ventrally while the back-swimmer has a body laterally compressed. Both insects are about ½ in. in length.
by Roy Alexander Harrison, D.SC., Senior Lecturer in Agricultural Zoology, Lincoln Agricultural College.