Length: typically about 3 mm in the genus
Members of the genus Stenelmis are found in streams, feeding both as larvae and adults by gathering detritus and scraping nutrients from rocks. Some members of the genus are flightless, while others fly for a brief period soon after leaving the pupa.
Each species in Stenelmis takes one, two, or three years to complete development. Researchers have found the period required for development of the various species has ranged from six months to three years. The former time period was in a laboratory setting and may not be duplicated in nature. It appears some species go through five larval instars and some seven (Tavares, 1990; White, 1978).
Interestingly, newly emerged adults are often found at lights, and as White reports, can remain out of water for several days. Once the adults have been living in a stream, however, they will die within a few hours after being removed from the water.
A related family is Byrrhidae, the Pill Beetles.
Note: At present this is the only page in the family Elmidae on the American Insects site.