Only the size of a strawberry seed, this aquatic beetle lives in and out of the bubbling, boiling spring openings found in the headwaters of the San Marcos and Comal Spring complexes that are fed by Edwards Balcones Fault Zone Aquifer groundwater. This species was listed as endangered in 1997, because threats of groundwater overconsumption and contamination. The U.S. Fish and Wildlife Service works with our partners to ensure the springs continue to provide clean and healthy freshwater to their microhabitats and important life history and biological research to address the needs for the species.
Heterelmis glabra is morphologically similar to the Comal Springs riffle beetle, but occupy different habitats. Heterelmis glabra can be found in rivers or streams from the southwestern United States, Central America and Mexico.
Microcylloepus pusillus co-occurs in the same habitats at the Comal Springs riffle beetle, but are often observed to be smaller and darker in color. These observations alone are not best to distinguish between the two species because of sampler bias. One key identifier is the indentations found on the prothorax, or mid-segment, on the top part of their body. The Comal Springs riffle beetle has a horizontal line and Microcylloepus pusillus has a Y-shaped indent down the center of the prothorax. A flashlight and a microscope will help you properly distinguish between the two species.
Stenelmis sp. co-occurs in the same habitats at the Comal Springs riffle beetle, but are larger about the length of a grain of rice. This species is dark brown and may appear to have a white or lighter color head, but may not always present. This change in color comes from the amount of oxygen held by the plastron.
Areas where ground water meets the surface.
Crawling on submerged gravel and decaying wood in close proximity to the spring openings, the Comal Springs riffle beetle eats organic matter, known as awfuchs or biofilm, off the roots and wood.
This fully-aquatic riffle beetle cannot fly and does not have gills. Instead, they encapsulate a bubble of air called a plastron that diffuses oxygen to their body and relies on good quality freshwater to survive.
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