Comal Springs Riffle Beetle

Heterelmis comalensis

Description

The Heterelmis comalensis (Comal Springs riffle beetle) is an aquatic, surface-dwelling species in the family Elmidae known from Comal Springs and San Marcos Springs. It was first collected in 1976 and was described in 1988. The closest relative of H. comalensis appears to be H. glabra, a species that occurs farther to the west in the Big Bend region. Adult Comal Springs riffle beetles are about 0.12 in (3 mm) long, with females slightly larger than males. The Comal Springs riffle beetle is not a subterranean species. Some riffle beetle species can fly, but the hind wings of H. comalensis are short and almost certainly non-functional, making the species incapable of this mode of dispersal. Larvae have been collected with adults in the gravel substrate of the spring headwaters and not on submerged wood as is typical of most Heterelmis species.

Behavior

The Comal Springs riffle beetle forages in aquatic gravel, and is flightless. Its food is unknown, but it is probably a predator of other invertebrates.

Habitat

It occurs in the gravel substrate and shallow riffles in spring runs. Usual water depth in this occupied habitat is 1-4 in (2.5-10 cm), although the beetle may also occur in slightly deeper areas within the spring runs.

Distribution

Populations are reported to reach their greatest densities from February to April. The Comal Springs riffle beetle has been collected from spring runs at Comal Springs in Landa Park and a single specimen was collected from San Marcos Springs 20 mi (32 km) to the northeast.

Threats

The primary threat to the Comal Springs riffle beetle is a decrease in water quantity and quality as a result of water withdrawal throughout the San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer. Groundwater pollution from human activities threatens to seriously degrade the water quality of its habitat as well.

Conservation and Recovery

The Comal Springs riffle beetle is only known from Comal Springs and San Marcos Springs. The rare beetle will only survive if its critical habitat at these springs is protected, and the essential hydro-logical and water-quality characteristics are conserved. The primary threat is associated with the withdrawal of water from the San Antonio segment of the Edwards Aquifer, so it is crucial that this hydrological use is limited to an intensity that does not degrade the critical habitat. The acceptable rate of water use by humans will have to be determined, and will have to account for the effects of periodic drought on groundwater recharge. It will also be necessary to control the risks of local spills of pesticides, hydrocarbon fuels, fertilizers, and other chemicals, any of which could seriously degrade groundwater and damage habitat. The populations of the Comal Springs riffle beetle will have to be monitored, and research undertaken into its basic biology and habitat needs.

Contacts

U. S. Fish and Wildlife Service
Ecological Services Field Office
Harland Bank Building
10711 Burnet Road, Suite 200
Austin, Texas, 78758-4460.
Telephone: (512) 490-0057

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

Reference

U.S. Fish and Wildlife Service. 18 December 1997. "Endangered and Threatened Wildlife and Plants: Final Rule To List Three Aquatic Invertebrates in Comal and Hays Counties, TX, as Endangered." Federal Register 62(243):66295-66304.