A water bug is a type of aquatic insect. Often people call a common house pest a water bug, but that bug is actually a large type of cockroach. Bugs in this category can belong to several different families, including the Notonectidae, Nepidae and Belostomatidae families. Water bugs are scientifically classified as belonging to the Hemiptera order. Boatmen (Corixade), water scorpions (Nepidae) and backswimmers (Notonectidae) are some of the most well-known waterbugs. Sometimes, however, the name water bug is used to refer to giant water bugs (Belostomatidae) to the exclusion of these other types of bugs.
Giant water bugs outdistance all the other aquatic bugs, coming in at more than 4.5 inches (11 cm) in length. These bugs are strong fliers and have mouth parts capable of piercing and sucking. A bite from one of these bugs can be serious, as they inject enzymes that break up proteins in their victims' bodies. Besides piercing mouths, these bugs have pointed beaks on the bottom portion of their heads; they also have wings that form an x-like pattern, overlapping the back portion of their abdomens. They eat fish, birds and various water animals.
Water boatmen are much smaller than the giant water bug, measuring about 1/2 inch (1.27 cm) long. They have long, hairy legs that are similar to boat oars on the back portions of their bodies and wide, rounded heads fitted with big eyes and rather short antennas. They have flattened bodies that are more long than wide. Their coloring is typically dull and mottled, and they are often confused with backswimmers because they are shaped similarly. This type of water bug swims upside down and has wings that are a lighter shade than its legs; they eat plant material, such as algae.
Water scorpions are a bit larger, coming in at about 1 to 2 inches (2.5 to 5 cm) long. These water bugs resemble land-based scorpions and have tails that look like whips. Surprisingly, these tails are actually breathing tubes. They have forelegs that resemble pincers, which they use to grab their prey, and they are meat eaters, consuming various pond animals. They do deliver a rather painful bite, but it is not as dangerous as a bite from a land scorpion.
Backswimmers are predators that swim upside down and have long hind legs that they use as oars. Their bodies are shaped like boats, and their abdomens are shaped like broad keels. Their underparts are lighter than their upper bodies, perhaps to help in camouflaging them when they swim. They can deliver painful bites, and they typically eat bloodworms and larvae. This type of water bug also carries an air bubble for breathing when underwater.