THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Beetles are the most diverse group of organisms in the world! To date, about 1 out of every 4 species of plant, animal, bacterium, and fungus that has been described by science is a species of beetle. A wonderfully diverse subset of those beetles live in freshwater wetlands, as most of the aquatic beetle families prefer still or slow water. Many families can be collected in a variety of wetland habitats, from pools and mossy bogs to tree holes.

Many aquatic beetles are benthic, lliving on or in the substrate. Others, such as adult whirligig (Gyrinidae) or predaceious diving beetles ( Dytiscidae) swim within the water column or on the water surface. The most commonly encountered Coleoptera in Pacific Northwest wetlands are Dytiscidae, Haliplidae (crawling water beetles) and Hydrophilidae (water scavenger beetles). Some families, such as riffle beetles (Elmidae) and long-toed water beetles (Dryopidae) do not regularly inhabit wetlands because they prefer faster moving waters. As with the rest of this guide, the focus of the beetle section is on the taxa most likely to be found in wetlands, but taxa less likely to be found are also included, in separate links.

Most of us see beetles such as lady bugs, June bugs, and ground beetles on a regular basis, and are familiar with the general appearance of an adult beetle. However, all Coleoptera go through complete metamorphosis, with a very different-looking larval form that pupates and emerges as the more easily recognized adult. Adult aquatic beetles share many of the features we identify with beetles in our daily lives and are fairly recognizable. Beetle larvae, on the other hand, are usually much more cryptic and hidden from view, so you may not be as familiar with them. If you ever bought mealworms from a pet store, you'll have a head start on recognizing aquatic beetle larvae when you come across them!