Coleoptera (beetles)

Order Coleoptera Description

Coleoptera is the largest insect order including over 5,000 aquatic species.  Beetles occupy a wide variety of habitats, but they never reach the same population densities as the common Ephemeroptera (mayflies) or Trichoptera (caddisflies).  Most aquatic beetles live in the substrate at the bottom of rivers and lakes, usually in cracks or self-made burrows. They occur in the greatest diversity in lentic habitats along pond edges or slow moving streams.


Coleoptera Families:
Click on each to display information below .


DryopidaeFamily Dryopidae

Long-toed Water Beetles

This family of aquatic insets is unique in the fact that the adult stage, and not the larval stage is aquatic.  Dryopid adults are most frequently found in the fast moving current of streams and rivers especially under rocks and submerged logs.  The adult's body is hard and the average body length is between 5 and 6.5 mm.  Dryopids have short antennae that are difficult to see because they are hidden beneath part of the head. 


Coleoptera Life History
Larvae and Pupae
Most species of Coleoptera pupate terrestrially.  The length and number of instars in the larval stage are variable between species.  In many species the larval stage is shorter than the adult stage, so the adult is found more frequently.

Adult Coleoptera generally live for only one season.  The adults of most species reside in the same aquatic habitat as the larvae, but they may leave on dispersal flights to find mates elsewhere if the present conditions are not optimal. The length of the adult stage varies with each individual species.  Eggs are deposited underwater or into submerged plant tissue; eggs usually hatch in 1 to 2 weeks.

Feeding Habits
Feeding is very variable among families of aquatic beetles.  Some Coleoptera are predators that engulf their prey or inject digestive enzymes through piercing mouth parts, while others, including the water penny, are scrapers that feed on detritus and algae. 


© 2007 by the Board of Regents of the University of Wisconsin System, UW-Extension provides equal opportunities in employment and programming, including Title IX requirements. UW-Extension programs are open to all persons without regard to race, color, ethnic background, or economic circumstances. All rights reserved.
Citizen Water Monitoring Network Home l Contact l UWEX Water Resources l Wisconsin DNR | Citizen Monitoring Network