From Ohio History Central
It is easy to see where backswimmers (Notonecta undulata) get their name. They spend most of their lives swimming on their backs. Because they swim upside down, their light brown, half-inch long bodies are shaped something like a boat, with the top portion of their body keel-shaped. Their strong back legs resemble boat oars and are used to propel them through the water. The other legs of the backswimmer are also for special functions; the first pair is for grabbing prey and the middle pair is for holding things.
Backswimmers are found throughout Ohio in habitats of ponds, lakes and slow-moving streams.
Backswimmers breathe by capturing a layer of air and clutching it to their abdomen with tiny hairs. The air is absorbed into their abdomen through openings called spiracles. They then return to the surface for more oxygen.
Another unusual characteristic is that their bodies are colored in a way that is opposite of most other animals. Instead of being dark-colored on top and light-colored on the bottom, backswimmers, because of their upside down lifestyle, are darker on the bottom than on the top. This helps them with camouflage from underwater predators such as water scorpions, giant water bugs and diving beetles.
They are aggressive predators themselves. They will prey on animals much larger than themselves, including tadpoles and small fish. Other diet includes small crustaceans; mosquito larvae; water fleas and other aquatic insects and organisms; and land insects that fall onto the water's surface Using sucking mouth parts, they extract bodily juices from their prey.
Backswimmers have a very painful bite and are sometimes called water bees because of the reaction that occurs.