A look at Marnock Cave. One of San Antonio’s caves.

Marnock Cave is one of the estimated 500 caves in San Antonio, Texas. This news article will explain what Marnock Cave is.

Marnock Cave is located ½ mile north of Helotes, Texas. This cave is the type locality but the exact physical cave location is unknown, therefore the cave name may be synonymous with another caves. (Ref: https://www.edwardsaquifer.net/pdf/karst_invertebrate_recovery_plan.pdf)

Marnock Cave lies within the approximately 4-acre John Wagner Ranch Cave #3 preserve (John Wagner Ranch Cave Preserve) within a small residential neighborhood in the Grey Forest area of northwestern Bexar County. Land to the east, west, and south of the preserve area contains low density (1-5 acres) occupied residential lots. Land to the north consists of undeveloped scrubby ranch land and woodland. A relatively high diversity of troglobitic species coupled with presence of low-density residential areas immediately to the east, west, and south and a large tract of undeveloped land to the north made acquisition and management of the preserve area highly desirable.

Its surface water drainage is a slightly oval, 52-m-long by 43-m-wide area that drains sheetwash into the cave’s entrance. In the direction perpendicular to the axis of the cave, the groundwater basin boundary should extend 20 m from the footprint of John Wagner Ranch Cave No. 3, plus an additional 10 m to include a probable collapse area at the cave’s northeast end. This is the likely groundwater drainage area since in feeding conduits and passages in other caves seldom reach greater distances from their main phreatic voids. (Ref: https://www.fws.gov/southwest/es/Documents/R2ES/Bexar_Cnty_Inverts_Delineation_of_Hydrogeologic_Areas.pdf)

John Wagner Ranch Cave No. 3 is frequently visited by locals which is why trash can be seen along with frequent signs of vandalism. Residents of San Antonio are aware of the existence of this cave.

The La Cantera Habitat Conservation Plan is the Karst Manager for Marnock Cave. John Wagner Ranch Cave No. 3 is synonymous with Marnock Cave. (Ref: https://www.fws.gov/southwest/es/Documents/R2ES/Bexar_RP_Distribution.pdf)

The John Wagner Ranch Preserve is managed per the La Cantera Habitat Conservation Plan since 2001. Management for this cave includes biannual RIFA treatment, biannual faunal monitoring, biannual cave cricket exit counts, and monthly surface inspections. (Ref: https://www.fws.gov/southwest/es/Documents/R2ES/Bexar_County_Karst_Invertebrates_5-Year_Review_Sep2011.pdf)

John Wagner Ranch Cave No. 3, and Fat Man's Nightmare Cave are located at the University of Texas at San Antonio (UTSA) and are included in the La Cantera Habitat Conservation Plan (LCHCP). (Ref: https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.120568/Rhadine_infernalis)

Rhadine exilis is a small beetle which inhabits John Wagner Ranch Cave No. 3. This species has been collected at Robber Baron Cave and tentatively identified from a juvenile specimen collected at John Wagner Ranch Cave No. 3. Distribution of this species of Rhadine exilis is known only from caves near Helotes and Camp Bullis. (Ref: https://books.google.com/books?id=L4Q-wsuDzQwC&pg=PA278&lpg=PA278)

The male holotype of Rhadine exilis can be found in Marnock Cave. The taxonomic classification is: Class Insecta (insects), Order Coleoptera (beetles), Suborder Adephaga, Family Carabidae (ground beetles), and Tribe Agonini (agonines). (Ref: https://www.fws.gov/southwest/es/Documents/R2ES/AUES_KarstInverts_Taxonomy.pdf)

J. F. Lawrence found Rhadine exilis running over wet walls and ceiling of Marnock Cave. The species coexists with R. i. infernalisin Marnock Cave and with R. i. ewersi in Headquarters Cave. Rhadine exilis is the most slender and depressed species in the genus, and by its form alone is readily distinguished from all other species of the subterranea group. It is presumably related most closely to speca and austinica because of itsmorphological attributes. There are 10 paratypes from Marnock Cave. Both infernalis infernalis and infernalis ewersi coexist with the extremely slender R. exilis, and are more abundant thanexilis except in Marnock Cave. The tips of the terminal palpal segments are not finely truncate. (Ref: https://digitallibrary.amnh.org/bitstream/handle/2246/5413/N2539.pdf?sequence=1)

This cave is the type locality for Rhadine exilis. While the habitat at John Wagner Ranch Cave No. 3 seems richer with nine known troglobites (the three La Cantera caves respectively have six, eight, and five troglobites), its high number is the result of numerous collections over the past 39 years and does not reflect the current low quality of the habitat. The cave should be protected, but it has too many problems of its own to serve as mitigation unless a larger and effective preserve can be established there and the habitat is restored. John Wagner Ranch Cave #3 lies within the UTSA karst region and contains the same possibility for C. madla as the La Cantera caves. Dr. James Cokendolpher, confirmed that the species identified in the John Wagner Ranch Cave #3 was more likely to be C. madla than any of the other three listed species of Cicurina. (Ref: https://casetext.com/case/center-for-biol-diversity-v-us-fish-wildlife-serv-4)

Species pairs of the subterranea group coexist in six caves: infernalis and exilis in Marnock, Headquarters, and Bat caves; speca and koepkei in Alzafar Cave; and subterranea and persephone in Tooth and Kretschmarr caves. Each of these three species pairs includes a "robust" species (infer-nalis, koepkei, persephone) and a "slender" one (exilis, speca, subterranea). In four caves the robust species is much more abundant than the slender one, but exilis was more abundant than infernalis in Marnock Cave, and in Alzafar Cave a single specimen of each species was found. These data suggest that the niches of the various species may overlap broadly, and that minimal overlap occurs between robust and slender species.

This is the most slender and depressed species in the genus. It is reddish-brown with an eye rudiment only 0.08 mm in diameter. Body length ranges from 7.0-8.4 mm. The pronotum is one-third as wide as long, widest behind middle, and possesses two pairs of marginal setae. Rhadine exilis is mostly closely related to R. speca speca, which occurs in Comal and Kendall counties. The two species may be most easily separated by the size of the eye rudiment (0.10 to 0.15 mm in R. speca speca versus 0.08 mm in R. exilis) and the width/length ratio of the pronotum (about 0.40 to 0.45 as wide as long in R. speca speca versus about 0.33 in R. exilis). The pronotum is also widest behind the middle in R. exilis whereas it is widest at or near the middle in R. speca speca. (Ref: https://www.edwardsaquifer.org/wp-content/uploads/2019/02/1999_Veni-etal_KarstSpeciesConservation.pdf)

Specimens of Texella inhabit John Wagner Ranch Cave No. 3. Additional specimens of Texella were also found in John Wagner Ranch Cave No. 3 due to a heavy fire ant infestation. (Ref: https://tpwd.texas.gov/business/grants/wildlife/section-6/docs/invertebrates/e1_j54_final_report.pdf)

John Wagner Ranch Cave #3 is the only cave on that ranch that has definitely yielded an immature eyeless Cicurina. Yes, based on known distributions that species is more likely to be C. madla than any of the other three listed Cicurina. Of course there is the possibility that it could be undescribed, but the proximity to Madla's Cave suggest otherwise. (Ref: https://www.fws.gov/southwest/es/Documents/R2ES/Bexar_County_Karst_Invertebrates_5-Year_Review_Sep2011.pdf)