Rhadine infernalis

Distinguished from the sympatric R. exilis by its thick rather than slender body, and by a pronotum that is wider and less elongated. R. infernalis has been observed closer to cave entrances than R. exilis. The two subspecies R. i. infernalis and R. i. ewersi are distinguished by subtle morphological differences established in the original descriptions by Barr (1960) and Barr & Lawrence (1960).

Small reddish-brown beetle with reduced eyes and elongated appendages characteristic of troglobitic adaptation. Body length ranges from 6.6 to 8.2 mm. Elytra are smooth. The neck is narrow, measuring less than half the width of the head. The pronotum is relatively wide and less elongated, bearing two pairs of setae. Body form is thick rather than slender.

Restricted to karst terrain in Bexar County, Texas, specifically caves and mesocaverns (small cavities inaccessible to humans). Karst habitats feature stable temperatures, high humidity maintained by water flow through limestone voids, and limited light. The species has been documented in 39 caves across five of six designated karst fauna regions within the county.

Endemic to Bexar County, Texas, United States. Known from 39 caves distributed across five karst fauna regions (KFRs) within the county: Stone Oak, UTSA, Helotes, Government Canyon, and Culebra Anticline. This represents the widest documented range of any endangered karst invertebrate in the region.

Observations from a limited study at Camp Bullis indicate activity primarily in spring and summer, with one fall record. Due to small sample size and the species' occupation of inaccessible mesocaverns, regular patterns of dormancy or activity remain undetermined.

Opportunistic feeder, consuming smaller or dead arthropods found in caves. Cave crickets (genus Ceuthophilus) and their eggs and nymphs are likely important food sources, as these crickets are abundant in Texas caves and serve as a documented food resource for karst invertebrates. Organic matter washed into caves from the surface may also contribute to nutrient availability.

Specific details unknown. As a troglobite, it likely exhibits characteristics common to cave-adapted invertebrates: relatively long lifespan, lower reproductive rate, and low metabolic rate, adaptations to conditions of limited food and stable environment. Direct development without larval stages is typical for Carabidae.

Occupies mesocaverns and cavities requiring excavation for access, making direct observation difficult. When active, found primarily under rocks. Observations suggest preference for areas of high organic content, including old bat guano. Believed capable of extended periods without food, retreating into very small inaccessible spaces during non-feeding periods, which may explain irregular detection. Most observations have been made near cave entrances relative to other troglobitic species.

Predator and scavenger within the nutrient-poor cave ecosystem. Functions as a consumer of arthropod detritus and potential predator of smaller cave invertebrates. Part of a trophic web dependent on surface-derived organic matter transported into caves, particularly by cave crickets that serve as a keystone resource for multiple endangered cave species.

Federally listed as endangered under the U.S. Endangered Species Act (2000), prompting conservation management of karst habitats in Bexar County. Subject of recovery planning and establishment of Karst Fauna Areas. Threatened by urbanization, invasive species (particularly red imported fire ants), and groundwater pollution. Conservation efforts include invasive ant control using containerized bait stations, establishment of preserves by the City of San Antonio and Texas Parks and Wildlife Department, and implementation of the Southern Edwards Plateau Habitat Conservation Plan.

• Rhadine exilisSympatric congeneric species in Bexar County karst; distinguished by slender body form and more elongated pronotum. R. infernalis has thicker body and wider, less elongated pronotum with two pairs of setae. R. exilis typically occurs deeper in caves than R. infernalis.

• troglobite
• cave beetle
• karst invertebrate
• endangered species
• Texas endemic
• ground beetle

• BugGuide
• Wikipedia
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• How Entomologists are Battling Invasive Ants to Protect a Texas Cave Ecosystem