Comal Springs Dryopid Beetle - Edwards Aquifer Authority

Comal Springs Dryopid Beetle

Covered Species Information

Authored by Connor Helsel
The Comal Springs dryopid beetle (Stygoparnus comalensis) is a subterranean aquatic beetle found exclusively in the Comal and San Marcos Spring systems of the Edwards Aquifer in Central Texas. The foremost threat to the species is over extraction of water from the aquifer, as Comal Springs dryopid beetles rely on consistent levels of springflow in and around the spring openings they inhabit (U.S. Fish and Wildlife Service [USFWS], 1997). The Edwards Aquifer Habitat Conservation Plan implements water quality monitoring and Conservation Measures such as the Voluntary Irrigation Suspension Program Option and the Aquifer Storage and Recovery programs to help maintain springflow for these aquifer dwelling species.

Common name

Comal Springs dryopid beetle

Scientific name

Stygoparnus comalensis

Endangered Species Act status

Endangered

Maximum size

Reach a size of approximately 3 mm (~0.12 inches; USFWS, 1997).

Physical description and Life History

The Comal Springs dryopid beetle is the only known subterranean member of the family Dryopidae (USFWS, 1997). Physically, the species has non-functioning eyes and wings, a reddish-brown and thinly pigmented, translucent body, segmented antennae, and has been described as the “long-toed water beetles” (Arsuffi, 1993; USFWS, 1997).

The Comal Springs dryopid beetles respire underwater via a plastron, a mass of setae on the underside that work to trap a thin layer of air and force the diffusion of dissolved oxygen from the surrounding water (Brown, 1987; USFWS, 2013a). This method of respiration is most effective is areas with ample springflow, since high springflow equates to increased levels of dissolved oxygen in the water (USFWS, 2013a).

Comal Springs dryopid beetles are most commonly found in subterranean areas where little is known of their behavior, reproduction, and lifespan in the wild. Though, it is believed that larvae are laid in air filled voids within spring openings as all other known dryopid beetle larvae are terrestrial and inhabit moist soil along stream banks (Brown, 1987; Kosnicki et al., 2019; USFWS, 1997). The Comal Springs dryopid beetle cannot swim and the exact depth to which this species navigates within spring opening is unknown (USFWS, 1997).

Distribution

In and around spring orifices of Comal and San Marcos Springs, more specifically in Landa Lake, Spring Lake, Hueco Springs, and Fern Bank Springs (Gibson et al., 2008; USFWS, 2013a).

Habitat and Diet

Critical habitat for the Comal Springs dryopid beetle is designated as 39.4 acres of surface and 139 acres of subsurface, specifically the beetle has been collected within 360 ft (110 m) of spring orifices (USFWS, 2013b). Comal Springs dryopid beetles have been consistently collected in and around the roots of sycamore trees growing near spring openings; these root mats may serve as the primary habitat of the species (Kosnicki et al., 2019).

The required temperature range of the Comal Springs dryopid beetle is that of the springwater at Comal and San Marcos Springs, 22 to 24°C (Edwards Aquifer Recovery Implementation Program, 2012; USFW, 2013b).

Diet is thought to be comprised of bacterial biofilms of decomposing leaf and wood material, particularly that of sycamore roots, although the precise food source remains unknown (Kosnicki et al., 2019; USFWS, 2013a).

References

Arsuffi, T. L. (1993). Status of the Comal Springs riffle beetle (Heterelmis comalensis), Peck’s cave amphipod (Stygobromus pecki), and the Comal Springs dryopid beetle (Stygoparnus comalensis) from Central Texas. Prepared for the U.S. Fish and Wildlife Service.

Brown, H. P. (1987). Biology of riffle beetles. Annual review of entomology, 32(1), 253-273.

Chapman, R. F. (1982). The Insects: Structure and Function. Harvard University Press, Cambridge, MA.

Edwards Aquifer Recovery Implementation Program. (2012). Habitat Conservation Plan. 414.

Gibson, J. R., Harden, S. J., & Fries, J. N. (2008). Survey and Distribution of Invertebrates from Selected Springs of the Edwards Aquifer in Comal and Hays Counties, Texas. The Southwestern Naturalist, 53(1), 74–84.

Kosnicki, E., Julius, E., & BIO-WEST, Inc. (2019). Life-history aspects of the Comal Springs dryopid beetle (Stygoparnus comalensis) and notes on life-history aspects of the Comal Springs riffle beetle (Heterelmis comalensis). https://doi.org/10.13140/RG.2.2.36307.94248

National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. https://doi.org/10.17226/25200

U.S. Fish and Wildlife Service. (1997). Endangered and Threatened Wildlife and Plants Final Rule to List Three Aquatic Invertebrates in Comal and Hays Counties, TX, as Endangered; final rule. 62 Fed. Reg. 242 (December 18, 1997) (to be codified at 50 C.F.R. pt. 17).

U.S. Fish and Wildlife Service. (2013a). Biological Opinion for the Edwards Aquifer Recovery Implementation Program HCP (No. 21450-2010-F-0110; pp. 52–57). Ecological Services Field Office. Austin, TX.

U.S. Fish and Wildlife Service. (2013b). Endangered and Threatened Wildlife and Plants; Revised Critical Habitat for the Comal Springs Dryopid Beetle, Comal Springs Riffle Beetle, and Peck’s Cave Amphipod; final rule. 74 Fed. Reg. 2013-09895 (Oct. 23, 2013) (to be codified at 50 C.F.R. pt. 17).

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