Owen et al.
Feeding on Ceuthophilus secretus (Orthoptera, Thaphidophoridae) by Rhadine austinica (Coleoptera, Carabidae) Barr 1974 in a central Texas cave
Jacob D. Owen1,2, Liza Colucci1, & Jeremy D. Maikoetter1
1 Zara Environmental, LLC, 1707 W. FM 1626, Manchaca, Texas 78652, USA 2 [email protected] (corresponding author)
Key Words: cricket, Ceuthophilus cunicularis, ground beetle, Rhadine austinica, Coleoptera, Carabidae, Austin, Texas, karst, subterranean, urban.
The genus Ceuthophilus (Insecta: Orthoptera: Rhaphidophoridae) currently consists of 89 species throughout North America (Taylor et al. 2007). The majority of known caves contain relatively low-energy ecosystems with primary producers absent (Gers 1998; Simon et al. 2003; Simon 2019). Cave crickets are known to introduce energy into cave ecosystems by first foraging at night on the surface and subsequently roosting within caves during the daytime where they eventually deposit feces, eggs, and their dead bodies (Barr 1967; Barr and Kuehne 1971; USFWS 2003; Taylor et al. 2005), ultimately driving the framework for a troglobitic food chain (Taylor et al. 2007). Smaller cave invertebrates, such as springtails, feed on the cave cricket guano, thus supporting predators such as troglobitic Cicurina spp. spiders (Araneae, Dictynidae) (Cokendolpher 2004). Cave cricket eggs are depredated by cave-adapted Rhadine spp. ground beetles (Coleoptera, Carabidae) (e.g., Taylor 2005), while other relationships are poorly understood despite the ubiquitous presence of cave crickets throughout there range. Cave cricket roles in the cave ecosystem are expected to hold value as indicators of health, where more cave crickets potentially signify a healthy and operating subterranean ecosystem and conversely less cave crickets could mean potential degradation in the subterranean ecosystem (Taylor et al. 2005; Lavoie et al. 2007). There are three species of cave crickets, Ceuthophilus secretus Scudder, 1894, Ceuthophilus cunicularis Hubbell, 1936, and an undescribed Ceuthophilus species that co-occur in central Texas caves containing federally listed karst invertebrate species or species of concern (Balcones Canyonland Preserve 2014). Of these three, Ceuthophilus secretus is the most studied (see Taylor et al. 2005; Taylor et al. 2007; Owen et al. 2016; Weckstein et al. 2016), primarily due to this species behavior of terrestrially foraging at night allowing researchers to document movement (Taylor et al., 2005) and population structures (Owen et al. 2016). Both C. secretus and the undescribed Ceuthophilus species both forage at night, whereas C. cunicularis rarely leave caves (Taylor et al. 2007). Cave cricket natural history is poorly documented in the highly karstic landscape of central Texas (e.g., Mitchell 1971; Taylor et al. 2005; Owen et al. 2016) and central Texas karst species conservation effectiveness potentially relies on obtaining more baseline data on cave cricket natural history (Owen et al. 2016).
The North American ground beetle genus Rhadine (LeConte) (Insecta: Coleoptera: Carabidae), are flightless ground beetles notable for their slender bodies and relatively
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long legs (Gómez et al. 2016). These beetles range from Canada south to Oaxaca, Mexico with the southwestern United States having the greatest diversity of species (Mitchell 1971; Barr 1974; Gómez et al. 2016). There are approximately 50 species in habitats that include mammal burrows, cellars and mine shafts, crevices in rock piles, and caves (Barr 1960; Barr 1974). The troglobitic (cave inhabiting) Rhadine species are abundant and speciose in the central Texas limestone caves found throughout the Balcones Fault Zone (Bousquet 2012). Most troglobitic Rhadine spp. are geographically separated and known from only one or few localities (Barr and Kuehne 1971; Reddell 1994), which has led to federal listing for some species (Reddell 1994). Life history traits, such as reproduction and early life stages of Rhadine spp. are poorly understudy and information on life history traits are needed for all troglobitic ground beetles (Elliott 1994). Basic life history data, such as diet, are lacking for Rhadine spp. (USFWS 1994) with rare documentation of Rhadine spp. being predators or opportunistic feeders of co-habiting invertebrates and cave cricket eggs. Mitchell (1971) and Taylor et al. (2007) suggest that troglobitic Rhadine and cave crickets share a predator-prey relationship and that Rhadine spp. are reliant on the cave cricket eggs. However, except for cave cricket eggs, feeding on cave crickets by Rhadine spp. has not been observed (Elliott 1994).
A wide-ranging species found in at least 39 known caves (south of the Colorado River and north of Hays County, Texas in central Texas; Balcones Canyonland Preserve 2014), R. austinica Barr, 1974 is a karst species of concern covered by the Balcones Canyonland Conservation Plan and not currently federally listed (Balcones Canyonland Preserve 2014). There are multiple nearby caves in central Texas that have the federally listed R. persephone Barr, 1974, although these two species do not co-occur.
Ceuthophilus sp. have been documented falsely digging oviposition holes, presumable to detract beetle depredation (Taylor et al. 2007). Troglobitic Rhadine are suggested as being highly endemic and major predators of subterranean environments. Other than egg predation there have been no confirmed predation events by Rhadine, particularly R. austinica, in published records, despite multiple circumstantial feeding observations (Elliott 1994). Here we report the first record of feeding on a deceased adult Ceuthophilus cunicularis by Rhadine austinica in a Texas cave.
Whirlpool Cave is located in South Austin, Travis County, Texas within the Whirlpool Cave preserve approximately 40 meters to the east of Highway Loop 1. Additional pedestrian roads are located directly adjacent to the preserve. The predominantly urban setting allows for easy and transparent access by the public. The cave supports a rich invertebrate fauna, including Balcones Canyonland Preserve species of special concern Cicurina bandida and R. austinica (Balcones Canyonland Preserve 2014).
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Figure 1. Travis County Room, Whirlpool Cave, Travis County, Austin, Texas.
In the early morning of 4 March 2019, as part of the regular cave atmosphere monitoring event, we entered Whirlpool Cave, southwest Austin, Texas (Figure 1), and encountered a dead Ceuthophilus cunicularis approximately 40 meters inside the cave adjacent to the crawl path. On closer examination of the corpse, we noticed a Rhadine austinica nearby and upon closer inspection of the deceased C. cunicularis, we observed another R. austinica on the abdomen of the C. cunicularis (Figure 2). We were able to photograph and video the feeding event, totaling approximately 10 minutes of observation time.
Cave crickets are generally abundant in subterranean environments (Lavoie et al. 2007). In central Texas, it is presumed that cave fauna are partially reliant upon the energy contributed to the cave environment by cave crickets, including their corpses. This is the first evidence of R. austinica feeding on a C. cunicularis carcass in a cave and presumed to be the first confirmed and documented report of Rhadine spp. feeding on a deceased adult cave cricket.
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Figure 2. Rhadine austinica predating on an adult deceased Ceuthophilus cunicularis. (A) shows the open wound on the C. cunicularis that the R. austinica was primarily focused during feeding. (B) The R. austinica has its head fully within the wound of the C. cunicularis.
Acknowledgements We are indebted to the Texas Cave Management Association, the Balcones Canyonlands Preserve and the City of Austin, specifically Nico Hauwert, PhD for allowing access and initiating progressive research on valuable natural resource sites.
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