[Photo: Texas Parks and Wildlife]

Comal Springs Riffle Beetle
Heterelmis comalensis

Description: The Comal Springs riffle beetle is a small aquatic beetle of the family Elmidae. It is approximately .07 inches (2 mm) long and .04 inches (1 mm) wide with females larger than males. The riffle beetle has short non-functional hind wings. It is brownish-yellow to dark brown in color, and covered with fine golden hair.

Life History: The Comal Springs riffle beetle feeds on microorganisms and debris scraped from the bottom of water bodies. The Comal Springs riffle beetle breeds year-round and its life cycle includes four stages: egg, larva (multiple instars), pupa, and adult. Other beetles of this genus have been shown to take anywhere from 6 months to 3 years to complete their life cycle, with the speed of this cycle heavily dependent upon environmental temperatures.

Habitat: This beetle's habitat includes the shallow, gravelly portion of spring runs at Comal, San Marcos, and Hueco Springs at 2-10 cm in depth, occasionally deeper.

Distribution: Heterelmis comalensis can be found at Comal, Hueco, and San Marcos Springs at the headwaters of the Comal and San Marcos Rivers in Comal and Hays counties, central Texas.

The map below depicts the critical habitat for this species, as designated by the US Fish and Wildlife Service pursuant to the Endangered Species Act.

NOTE: No warranty is given, expressed or implied, as to the accuracy, reliability, or completeness of these data. Data do not represent a legal description of the critical habitat boundary; refer to the textual description in the appropriate final rule for this species as published in the Federal Register.

Federally Designated Critical Habitat for the Comal Springs Riffle Beetle (Heterelmis comalensis) [Figure: Houston Advanced Research Center using US FWS data]

Status: The Comal Springs riffle beetle is a state and federally listed (1997) endangered species. There is a refugium for this species at the San Marcos National Fish Hatchery and Technology Center. The Comal Springs riffle beetle has an extremely small range, suggesting that it requires particular habitat characteristics to live. Thus, changes in the surface or groundwater quality or quantity associated with its habitat could cause extreme negative consequences for this population. Surface and groundwater quality threats associated with its habitat include constituents associated with human sewage, animal waste, agricultural chemicals and urban runoff. Because flowing water is required for respiration, optimal spring flows should be >150 cubic feet per second (cfs). The beetle begins to lose habitat at between 150 and 100 cfs and sustained low flows of 80 cfs or lower pose a possible legitimate risk to this population.

Resources:

Edwards Aquifer Authority, Draft Edwards Aquifer Habitat Conservation Plan

Texas Parks and Wildlife, Endangered Species of the Edwards Aquifer

Texas A&M, Comal Springs Riffle Beetle Status

US Fish and Wildlife Service Critical Habitat Final Rule

US Fish and Wildlife Service, Endangered Species Listing