Order Coleoptera (Beetles) 
Courtesy of the Cacapon InstituteHead has thick hardened skin; thorax and abdomen of most adult families have moderately hardened skin, several larvae have a soft-skinned abdomen; no wing pads on the thorax in most larvae, but wing pads are usually visible on adults; three pairs of segmented legs attach to the thorax; no structures or projections extent from the sides of the abdomen in most adult families, but some larval stages have flat plates or filaments; no prolegs or long tapering filaments at the end of the abdomen.  Beetles are one of the most diverse the insect groups, but are not as common in aquatic environments.  Most of the adult stages of the families listed here are aquatic or semi-aquatic. 


Chrysomelidae (Reed beetle): The body is soft; three-pairs of segmented legs attached to the thorax and two hooks on the lower end of the abdomen. Crawler; Collector/gatherer; S-M (H)(S)


Dryopidae (Long-toed beetle): Adults are hard bodied with very short comb-like antennae.  The family is similar in appearance to Elmidae.  The larva  of this beetle is not aquatic but may be found in the splash zone. Clinger/crawler; Shredder; VS-S (M)(S)


Dytiscidae (Predacious diving beetle): Legs have five-segments and two-claws on the end; abdomen terminates into a pair of filamentsAdult: slender antennae; hind coxae extends posterior dividing the first abdominal segment into two sections. Swimmer/crawler; Predator; VS-VL (M)(S)


Elmidae (Riffle beetle): Larvae: Legs with four segments and a single claw; nine abdominal segments some with a cavity that protect the hind gills Adult: hard bodied, slender sometimes clubbed antennae; the forewings have numerous rows of indentations; legs long compared to body. Clinger/crawler; Scraper/shredder; VS-S (M)(F)


Gyrinidae (Whirligig beetle): Two claws of each leg, legs with five segments; ten abdominal segments with pairs of lateral filaments.  Adult: compound eyes, which appear divided into pairs; antennae clubbed; mid and hind legs paddle-like. Swimmer/crawler; Predator; S-L (M)(S/F)


Haliplidae (Crawling water beetle): Legs with five segments and a single claw; abdomen terminates into long filaments; some have many long slender filaments along the entire length of the body. Adult: antennae long and slender; forewings have many indentations; legs lined with small hairs for swimming. Swimmer/crawler; Shredder; S-M (H)(S)


Hydrophilidae (Water scavenger beetle): Large mandibles; legs with four segments and a single claw; end of the abdomen usually blunt.  Adult: antennae clubbed with cup-like segments at the base; hind coxae (joined base) do not extend or divide the abdomen. Swimmer/crawler; Predator; VS-VL (H)(S)


Ptilodactylidae (Toe-winged beetle): Legs with four segments and a single claw; abdomen has ventral gills.  Very similar in appearance to the riffle beetle larva.  Clinger/crawler; Scraper/shredder; VS-S (M)(F)


Psephenidae (Water penny): Body flattened with thoracic and abdominal segments expanded so that the legs and head are obscured from above; legs terminate into a single claw.  The adult is semi-aquatic, sometimes encountered near the stream. Clinger/crawler; Scraper; VS-M (L)(F)