Giant Diving Beetles are members of a family collectively called predatory diving beetles. They all live in the water and are voracious predators that will often take prey larger than themselves. There are about 150 species of predatory diving beetles in the United States and Canada, ranging in size from about 1.5 mm to 40 mm (1/16 of and inch to about 1-1/2 inches).
Identification of these species is tricky. Any
bug that is over about 20 mm will undoubtedly can be called a Giant Diving Beetle. Most species of
diving beetles are dark brown or black, often with a lighter brown or reddish brown border, and some having a lighter band across the back near the hind end. The hind legs, which are used for swimming, are the longest, and have long hairs on them. The larvae, which are called water tigers, are elongate, with a large head and powerful jaws. They swim using all three pairs of legs and usually have the tail end sticking up in the air.
Both adults and larvae are voracious predators, and will devour a wide variety of insects and other invertebrates, as well as vertebrates such as frogs, toads, salamanders and small fish. The adults have mandibles that allow them to tear their prey apart. The larvae have jaws like hypodermic needles that allow them to inject digestive enzymes into their prey. These enzymes dissolve the body tissues and the water tiger sucks up the resulting liquid.Water beetles are often used as indicators of wetland habitat and quality. These beetles respond quickly and predictably to changes in pH balance, salinity (saltiness) and levels of organic pollution in water. Scientists can learn about the quality of water for supporting wildlife by closely monitoring water beetles.
Both adults and larvae come to the surface to breathe by sticking the back end out of the water. Adults carry air under the wing covers, and often have a small bubble attached to the back of the abdomen. Adults come out of the water at night and fly around. Because they use the moon to navigate, they are attracted to any bright light. For this reason they are often found under porch lights, street lights and gas station lights.