GIANT DIVING BEETLE & WATER TIGER

Bug Index

Assassin Bug

Bigeyed Bug

Firefly

Bumblebee

Damselfly

Dragonfly

Giant Diving Beetle

Giant Stoneflies

Giant Water Bug

Ground Beetles

Honey Bee

Lacewings

Ladybird Beetle

Mealybug-Destroyers 

Millipede

Pirate Bugs

Praying Mantid

Predatory Mites

Rove Beetles

Sowbug

Syphid Fly

Tachnid Fly

Yellow Jacket

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. 

They can be found wherever there are ponds, sloughs, lakes, streams and rivers. They are not found in fast-moving water. Adults and larvae of various species can be found throughout the spring, summer and fall. The adults of some species move from shallow bodies of water in the fall to deeper lakes where they remain active all winter long under the ice. As mentioned above, these insects are aquatic in the larval and adult stages. The larvae do, however, come out onto dry land to pupate. 

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. 

Giant Diving Beetles, when they turn up under a porch light or street light, often amaze people because of their large size. Although they have biting mouthparts, and can certainly give one a bit of a nip, they are not capable of doing any real damage. Gas stations with their bright lights and car lots, with the combination of bright lights and shiny reflective car tops, can attract large numbers of the medium-sized predatory diving beetles, to the point that they may even become a bit of a nuisance.