What does it look like?
Diving Beetles are usually brownish-black or dark green. They have chewing mouthparts. They range in size from 1/16 inch to 1-5/8 inches long. They have smooth, oval bodies and long, slender legs. Hind legs are often flat like paddles for swimming.
Small Flat Diving Beetles are only about ½ inch long. They have an oval, flattened body. They are brown with brownish-yellow markings. The hind legs are fringed with yellow hairs to help them swim.
Yellow-marked Diving Beetles are about 3/8 inch long. They have a black carapace (shell) with dull yellow edges and markings. Their hind legs are reddish-brown. Front legs and middle legs are dull yellow.
Marbled Diving Beetles are flat and oval shaped. They have a black, bony shell covering (carapace) with irregular gold markings. They have yellowish spots on the abdomen.
Predacious Diving Beetles are dark brown or black. The body is smooth and shiny. They are 1/8 to 1 inch long. There are spots, lines, or dappled colors on the wing covers (elytra). The antennae are thin. Their hind legs are flat with claws on the ends. Legs are fringed with hairs for swimming.
Great Diving Beetles are about 1 inch long. Their body is streamlined for fast swimming. Their color is dark brown to black with yellow legs. There is a yellow border around the head and mid-section (thorax) of the body. Spangled Diving Beetles are about ½ inch long. Sometimes they appear gold-colored. The edges of the body are black. They have swimming hairs on their legs.
Where does it live?
Diving Beetles are found in freshwater habitats: wetlands, marshes, and slow-moving streams. Sometimes they can be seen in ponds and puddles. Large Diving Beetles are found throughout North America. Small Flat Diving Beetles live in southern Canada and northern United States.
Marbled Diving Beetles live in Texas, Arizona, California, and Mexico. They are widespread in the northern United States and Canada.
Predacious Diving Beetles are found worldwide. There are about 500 species in North America. They live in freshwater habitats. Sometimes they live in salt water ponds. Adults and larvae are seen in spring, summer and fall. Adults of some species remain active in winter. They live under ice in deep lakes.
Great Diving Beetles are found in Britain, Europe, and northern Asia.
What does it eat?
Adult Diving Beetles and their larvae are predators. They eat other insects. They use their strong jaws to attack large prey. They eat frogs, toads, salamanders and small fish. Their larvae are called “water tigers,” because of their fierce appetites.
Marbled Diving Beetles eat small insects, water mites, and aquatic worms.
How does it defend itself?
Diving beetles are slow moving on land. They are food for birds and mammals. But in water, they move quickly to avoid predators. Their larvae are small and fast moving. In a small pond, they may be at the top of the food chain with no predators.
Some species can detect chemicals given off by predators.
Great Diving Beetles send out a foul-smelling fluid to keep predators away.
What stages of metamorphosis does it go through?
Diving beetles undergo complete metamorphosis. They grow from egg to larva, to pupa, and finally to adulthood. Larva eat a tremendous amount of food. As they grow they shed their outer covering (exoskeleton) many times. Then comes the pupal stage which usually happens in the winter.
Adults mate from spring to autumn. Most species lay eggs in moist soil. Some species insert a large egg mass into a water-plant stem. This keeps the eggs moist. Plant stems do not dry out as quickly as surface soils. They are also better hidden from predators.
What special behavior does it exhibit?
To swim, Diving Beetles move their hind legs together like oars rather than one at a time. They hold the tip of the abdomen up to the water surface to get air. Air is stored under their wing covers. They use the stored air when they are under water.
Adults fly around at night. They use the moon to navigate. They are attracted to outside lighting. They sometimes land on roads or shiny surfaces, mistaking them for water
In dry seasons, Predaceous Diving Beetles burrow into the sand and mud beneath streams. If their water habitat becomes too dry, they fly away to find a new one. Sometimes electric lights lure them to birdbaths and swimming pools.
How does it affect people?
Diving Beetles are beneficial because they eat other insects. They may play a role in controlling mosquitoes.
Their bite is painful but they are generally harmless to people. They are a bother when they swarm around bright lights.
Diving Beetles are pests in fish hatcheries where they eat baby fish (fry).
People in Mexico and Japan eat Diving Beetles.
Borror, D. J. & White, R. E. (1970). A field guide to insects of America north of Mexico. New York, NY: Houghton Mifflin Company.
Marshall, S. A. (2006). Insects and their natural history and diversity. Richmond Hill, Ont: Firefly Books.
McGavin, G. C. (2000). Insects, spiders and other terrestrial arthropods. New York, NY: Dorling Kindersley Inc.
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