INFORMATION

The Farallon Camel Cricket (F. cavernicolus) was first described by entomologist David C. Rentz in 1972 (Rentz, 1972). It is a member of the Rhaphidophoridae, or “Cave Cricket” family (Rentz, 1972). As the name suggests, Cave Crickets favor cool, damp, and dark areas, such as rotten logs, wells, stumps, and, of course, caves (Iowa State Institute, BugGuide). Species in this family share wingless, brownish bodies with a humpbacked appearance, long antennae, and large hindlegs (Iowa State Institute). 

The Farallon Cave Cricket is endemic to the Farallon Islands, an archipelago approximately 28 miles west of San Francisco, California (Valainis et al., April 2019; FWS). This species is the only known orthoptera on the islands, where it is primarily found in caves and shallow rock crevices alongside nesting Cassin’s Auklets, which provide food in the form of guano and carrion. (Rentz, 1972). However, crickets are opportunistic feeders known to consume almost anything they find (Valainis et al., January 2019). 

A distinctive characteristic of Cave Crickets is their tendency to gather closely together in groups of around 15 to 100 individuals in mutual antennal contact (Rentz, 1972; Valainis et al., January 2019). Individuals enter and leave the caves in clusters but tend to disperse upon disturbance, such as when light is shown on them, only to form new groups later (Valainis et al., January 2019). This behavior is not well understood, but may relate to the species’ sense of smell, taste, touch, and proprioception through antennae, believed to be mechanosensory and chemosensory organs. While mature crickets are typically found on cave walls and rock surfaces, immature crickets are often observed on cave floors, where they presumably land in an effort to escape cannibalism by older crickets (Valainis et al., January 2019). 

Like most Cave Crickets, this species is nocturnal and known to venture outside their subsurface habitat to forage for food (Valainis et al., January 2019). 

Recent research suggests that Cave Crickets are a keystone species in  subsurface ecosystems (USGS Mammoth Cave 2008, National Park Service Natural Resource Condition Assessment 2021, Poulson et al., 1995, Weckerly, 2012). By periodically foraging at or near the cave entrance, Cave Crickets produce guano and eggs which serve as critical nutrients to other species that live in otherwise energy-depauperate caves (Weckerly, 2012). Because Cave Crickets are vital to bringing resources into cave communities, they are often used as a basis for monitoring the health of cave ecosystems (USGS Mammoth Cave 2008, Poulson et al., 1995, Weckerly, 2012). Accordingly, threats to Cave Crickets are really threats to the cave ecosystem.  

CONSERVATION STATUS

The Farallon Camel Cricket has not been assessed by the IUCN but may qualify as Vulnerable on the basis of its restricted area of distribution, Extent of Occurrence (EOO), Area of Occupancy (AOO)), small population size, and suspected rate of decline  (IUCN Red List Criteria Summary Sheet). The Farallon Camel Cricket is restricted to the caves and crevices of the Farallon Islands, which total 211 ac (0.85 km2) (Valainis et al., April 2019; FWS). However, the species’ actual population size and trends are largely unknown as recent estimates have varied dramatically. 

According to the Project Feasibility and Non-Target Risk Trial Report for the proposed House Mouse Eradication project at the Farallon Islands, a survey conducted in 2010 counted approximately 1630-1830 crickets in five caves known to be home to the species (Pg. 22). However, with the introduction of biomarkers making crickets easier to see and count, estimates significantly increased and even quadrupled in some cases. A series of surveys conducted in 2013-2014 also suggest a greater abundance than previous estimates with a mean of 2790 ± 277 crickets found over nine samples in just one of the caves known to house the species (Valainis, et. al. 2018). More recently, surveys conducted by scientists stationed on the islands in partnership with the U.S. Fish and Wildlife Service have counted an average of 3397 individuals in Cricket Cave during fall counts from 2016 to 2020 (Point Blue 2020 Farallon Island Ecosystem Report (pg. 29)). 

Threats

Threats to the Farallon camel cricket population are also understudied but may include predation by The Farallon Island Arboreal Salamander (Aneides lugubris farallonensis), the House Mouse (Mus musculus), and the Burrowing Owl (Athene cunicularia). Anthropogenic stressors such as cave entrance disturbance by humans and rock-fall may also threaten the species by impeding foraging (Valainis, January 2019, Mammola et al., 2021). Climate change and weather may be an additional inhibiting factor, as Cave Crickets are known to be sensitive to temperature and humidity (Weckerly, 2012). That is, fluctuations in population abundance related to extreme weather conditions have been observed in similar species, and are believed to be the result of reduced foraging (Valainis, January 2019).

Conclusion

Caves and subterranean habitats are among the most “unique, secluded, understudied, and difficult-to-study environments on our planet” (Mammola et al., 2021). Consequently, specialized species, including the Farallon Camel Cricket, are among the least documented fauna on our planet as knowledge gaps currently impede the ability to protect cave ecosystems (Mammola et al., 2021).

Limited research exists explaining the diet, biological characteristics, and behaviors of most subterranean species, and the Farallon Camel Cricket species in particular. As such, threats to this species’ global population and its habitat are difficult to quantify. Basic knowledge as to the Farallon Camel Cricket diet, mating behavior, foraging behavior, and interactions within different subterranean communities is required to fully understand their role in the cave ecosystem, the potential threats to their survival, and, consequently, the Farallones’ unique subterranean ecosystem as a whole.