| Abstract |
he narrowfoot hygrotus diving beetle (Hygrotus diversipes Leech, 1966) is a rare and endemic aquatic beetle only known from central Wyoming. Hygrotus diversipes was discovered in 1964 and became a Category II Candidate Species under the Endangered Species Act in 1984, which led to surveys that discovered the beetle in 3 additional streams. We compiled historical data on H. diversipes and bolstered this data set with contemporary surveys to understand the species' distributions, trends, and habitat needs. Hygrotus diversipes lives in isolated pools of intermittent, shallow streams with mostly subsurface flows. All inhabited streams had high concentrations of salts (500–58,000 µS/cm). We began annual surveys in 2010 for H. diversipes in response to 3 petitions requesting federal protection between 2007 and 2013. Four streams were occupied during ≥33% of years, and we consider them core sites used by H. diversipes. Specific conductivity and pH explained the most environmental variation in occupied streams according to principal components analysis. Most pools occupied by H. diversipes hold water all summer, but hot, dry spells caused water levels to drop and specific conductivity to increase. Hygrotus diversipes is most common in smaller pools (<8 m long) with structure (e.g., woody vegetation and overhanging grass) that lack fish. This rare aquatic beetle was not warranted federal protection under the U.S. Endangered Species Act in 2023. |
, Audrey Lindsteadt 
