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NATURAL HISTORY

COMAL SPRINGS RIFFLE BEETLE } Heterelmis comalensis
FAMILY: Elmidae

DESCRIPTION: The Comal Springs riffle beetle is an aquatic, surface-dwelling species of about two millimeters in length, with females slightly larger than males. It is reddish brown in color and has short hind wings and a narrow body. The larva has an elongate, tubular body and can be up to 10 millimeters in length.

HABITAT: The Comal Springs riffle beetle occurs in gravel substrate and shallow riffles in spring runs. The water in occupied habitat is usually about one to four inches deep, although the beetle may also occur in slightly deeper areas within the spring runs.

RANGE: Comal Springs riffle beetles are known from three spring runs at Comal Springs in Landa Park, as well as San Marcos Springs, 20 miles to the northeast.

MIGRATION: This beetle has not been known to migrate.

BREEDING: Riffle beetles typically deposit eggs on the underside of submerged rocks and debris.

LIFE CYCLE: All beetles undergo complete metamorphosis with life cycles consisting of an egg, larva with multiple instars, pupa, and adult. All life stages except that of the egg make take place throughout the year.

FEEDING: Larval and adult riffle beetles both feed on microorganisms and debris scraped from the substrate.

THREATS: The main threat to the survival of the Comal Springs riffle beetle is decreased spring flow due to increased use of groundwater resources throughout the Edwards Aquifer region, which may prove fatal to the species when coupled with periodic drought. Other threats associated with increased urbanization include increased flooding and erosion, pollution, siltation, and storm-water runoff. Exotic species negatively affect the beetle through competition for food, displacement or destruction of aquatic vegetation, and general habitat degradation.

POPULATION TREND: Comal Springs riffle beetles have been collected from spring runs 1, 2 and 3 at Comal Springs and a single specimen was taken from San Marcos Springs. It is not known whether this species historically ranged in other springs that are now dry almost all the time, such as San Pedro Springs and San Antonio Springs.

Photo by Joe N. Fries, USFWS