Two monitoring methods for the endangered Comal Springs riffle beetle, Heterelmis comalensis Bosse, Tuff, and Brown, 1988, were evaluated. The first used cotton cloth “lures” lodged within the substrate in close proximity to spring openings. The second evaluated the feasibility of marking H. comalensis with paint. During our evaluation, biofilms grew upon the lures over time, and within two weeks H. comalensis were collected. Numbers of H. comalensis (mean = 23, range = 4–53) collected from lures peaked at 10 weeks and then began to decline as the cotton cloth lures began to decompose. Three other invertebrate species, the riffle beetle Microcylloepus pusillus (LeConte, 1852), the endangered Comal Springs dryopid beetle Stygoparnus comalensis Barr and Spangler, 1992, and the endangered Peck's cave amphipod, Stygobromus pecki (Holsinger, 1967), were also collected from the lures, suggesting that this technique may have broad applicability as a passive monitoring tool for interstitial aquatic endemics and other endangered species. All species, including H. comalensis, were readily quantified, and the technique allowed for specimens to be returned alive to their site of capture.Marking H. comalensis elytra with paint was a feasible technique because marks were retained for up to three months; however, it may be more practical for laboratory experimentation rather than field use because it is timeconsuming and labor intensive. Recapture rates for marked individuals were low in situ, most likely due to unknown factors such as movement, dispersal, and the ratio of individuals marked compared to the population size. Nevertheless, our evaluation suggests that these two techniques in combination may provide a valid means to monitor and evaluate population trends of H. comalensis without negatively affecting the species.