Experimental tests of habitat preferences in the Comal Springs dryopid beetle, Stygoparnus comalensis

The Comal Springs dryopid beetle, Stygoparnus comalensis Barr and Spangler (Coleoptera: Dryopidae), is a federally endangered species endemic to three spring systems in central Texas, United States. Improving our understanding of the biology of this species is necessary for making progress towards the goals of its protection: establishing a monitoring program and maintaining captive reproducing populations. A series of experiments were conducted in captivity to empirically examine habitat preferences of S. comalensis while using a similar co-occurring species, Stenelmis sexlineata Sanderson, for comparison. Stygoparnus comalensis had a strong affinity for wood over leaves and rocks and had fuller guts when offered wild-conditioned wood compared with captive-conditioned wood. Adults and larvae of S. sexlineata were also attracted to wood when offered rocks, but did not prefer wood when also offered leaves. Both species responded to light, but responses were light- and species-specific, with S. comalensis avoiding shorter wavelength light and being attracted to longer wavelength light whereas S. sexlineata seemed to hide from all light types. Both species were attracted to conspecifics but not heterospecifics. Stygoparnus comalensis did not exhibit any clear response to flowing water (S. sexlineata was not examined). These results provide insight into the potential adaptations of a spring-endemic beetle species and environmental relationships that can potentially be used for improving monitoring and conservation of wild populations.