Predacious Diving Beetle

Scientific name: Insecta Coleoptera

Common name(s): Predacious Diving Beetle

We've nicknamed the bug you see above, the predacious diving beetle, "zippity."

The predacious diving beetle is a seldomly seen but very common aquatic insect. In fact, there are over 500 in North America and over 5,000 worldwide. The reason they are so infrequently seen is that they spend nearly all of their lives in the water. The creature shown to the left is in the adult stage. This particular beetle is one of the largest of it's kind in North America, measuring approximately 1.5 inches long.

As their name implies, these beetles are predatory; that is, they eat other creatures — mainly bugs, although an occasional tadpole or small fish is not uncommon for the larger ones. The adults are very good swimmers and catch most of their prey live, eating it whole or in pieces. The larvae lie in wait near the waters surface and catch their prey with two large pincers. Then, they inject the captured bugged with juices that dissolve their insides. Once the inside of the bug is nice and juicy they suck out the insides like a mosquito sucks blood. Sometimes, when food is not abundant, predacious diving beetles will feed on something that is dead that they didn't kill. This is called scavenging.

Most predacious diving beetles hang out in wetlands and lakes, in and around vegetation and woody debris. Some are found in rivers, but not very many.

Predacious diving beetles are excellent swimmers. They have a very smooth and streamlined exoskelton. Their hind legs are covered with long hairs called natatory setae. They use these hairs like people use flippers, and they use them very well. In addtion to being fast swimmers, predacious diving beetles are well camouflaged and difficult to see. This makes them almost impossible to catch. But, if they are caught, many adult diving beetles emit a very distastful chemical. This keeps them from being preyed upon by fish and insect-eating waterfowl.

The larvae aren't good swimmers, but they're camouflaged well. If you see a large predacious diving beetle larvae, be careful. They've got two long pincers and can inflict a painful bite.

The next time you're standing on a dock and the water is calm, be very still and watch the water around the weeds. If you're lucky, you'll see a predacious diving beetle swim by. But don't blink, because they are fast.

Class: Insecta
Order: Coleoptera
Family:Dytiscidae
Genus: Dytiscus
Species: n/a

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More Info

Want to know more about Minnesota's water? Check out our Water page and find out more about the quality of Minnesota's water.

The creature highlighted on this page was collected by MPCA's Water Quality Lab. This lab samples and analyzes water from around Minnesota.