Common Backswimmer
Notonecta undulata
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These aquatic insects are about half an inch long and swim upside-down in rapid jerks. They use their long, flattened back legs, which are fringed with hairs, as oars. The underside (which faces up) is dark, and the back has an orange pattern on it. Backswimmers will come up underneath their prey to catch them. They are also capable of flying and do so to find more habitable areas.

Dorsal view
Ventral view