The Comal Springs riffle beetle (Heterelmis comalensis) is an endangered species inhabiting springs of the Edwards Aquifer. It is known to exist only in Comal spring in Guadalupe and Comal Counties, Texas, and San Marcos spring in Caldwell and Hays counties, Texas. This species is threatened by decreased water quality and quantity. We tested the association of H. comalensis to spring openings and assessed preference for several habitat variables in an effort to describe the determinants of the narrow range of the species. To test the association of beetles with the spring outlets, we buried meter-long cotton strips over spring habitat as lures and, after 4 wk, collected adults and larvae from the strips. We found beetle abundance was highest within 20 cm of the spring outlet and decreased gradually with distance from the spring source. We tested preferences for the following variables: well water, flow, carbon dioxide (CO₂), temperature, and light, using H. comalensis and Heterelmis vulnerata, a more-widespread species, as a comparison. Both species showed significant preferences for low flow, elevated CO₂, temperatures ~23°C, and darkness. They differed in that H. comalensis preferred well water while H. vulnerata did not. Based on our results, H. comalensis was found primarily in spring source habitat and preferred the water quality conditions found in these habitats.