(Odonata: Anisoptera: Gomphidae)
Erpetogomphus compositus is a North American species whose distribution extends from northwestern United States to northern Mexico. It is known from lotic, depositional habitats with fine sediments, including sandy rivers and streams. Although this species is globally secure, it is critically imperiled in Washington, possibly extirpated from Utah, and unranked in all other US states. Habitat disturbance and degradation are the main threats to this species, but adaptive land management practices, such as conserving and restoring riparian buffers around known aquatic habitats, may help protect this species.
Adult: Characteristic of the family Gomphidae, this species has small, widely separated eyes and enlarged posterior abdominal segments (often less apparent on females). The conspicuously pale-ringed abdomen and pale green thorax with four distinct dark stripes are diagnostic for this species (Paulson 1999). The thorax is whitish between one pair of stripes (Paulson 2007a). The wings are clear with a slight yellowing at their bases (Abbot 2007). Total length: 46-55 mm (1.8-2.2 in.); abdomen: 31-39 mm (1.2-1.5 in.); hindwing: 26-32 mm (1-1.3 in.). Additional descriptive information for the adult can be found at OdonataCentral: http://www.odonatacentral.org/index.php/FieldGuideAction.get/id/46076 (last accessed 5 Oct. 2008).
Immature: Erpetogomphus in the Pacific Northwest can be identified by the following traits: prementum and palpal lobes flat (as opposed to cup-shaped), antennae 4-segmented, wing pads divergent, labium wide (maximum width more than half maximum width of head across eyes), tips of cerci extending at least 0.9 times (as opposed to 0.75 times) the distance to the tip of epiproct (Tennessen 2007). Species identification is difficult for a non-expert.
Adult flight period varies by region: 19 June – 13 September in Oregon (Johnson and Valley 2005); 11 July -17 August in Washington (Paulson 2007b). The egg-laying strategy of this species involves hovering motionless over water and tapping the abdomen to the water surface (Abbott 2007). Like all odonates, the majority of the life cycle is spent as aquatic larvae. Larvae are predators of aquatic animals, mainly insect larvae, while adults prey on flying insects. NatureServe (2008) designates sightings more than 3 kilometers apart as separate populations, but little is known about the dispersal and colonization ability of this species.
Range-wide: Distribution extends from northwestern United States to northern Mexico. United States species records in: AZ, CA, ID, NM, NV, OR, TX, UT, WA, WY (NatureServe 2008).
Washington: Known from only Crab Creek, Grant Co., and the Yakima River, Benton Co. (Paulson 2007b).
Oregon: Primarily confined to areas east of the Cascade Range, up to 1370 m (4500 ft). Present in Gilliam, Grant, Harney, Malheur, Sherman, Wasco, and Wheeler counties (Abbott 2007). Particularly common along the John Day River in the Columbia Basin, a regional “hotspot” for lotic odonates. Also common at the Malheur and Owyhee Rivers (Johnson and Valley 2005).
The genus is generally known from lotic, depositional habitats with fine sediments (Merritt et al. 2008). The Washington collection records were in sandy streams and rivers (Paulson 2007b). This species inhabits desert streams, creeks and irrigation ditches with wide sandy or rocky margins in the Southwest (Abbott 2007). Often seen perched on sandbars of streams, and in shady, more protected areas in the late afternoon (Abbott 2007). The larvae are burrowers (Merritt et al. 2008).
Global Status (1990): G5
Rounded Global Status: G5 – Secure
National Status: N5
State Statuses- Arizona (SNR), California (SNR), Idaho (SNR), Nevada (SNR), New Mexico (SNR), Oregon (SNR), Texas (SNR), Utah (SH), Washington (S1), Wyoming (SNR)
Habitat disturbance and degradation are the main threats to this species. The larvae of this species require fine substrate for normal burrowing behavior. Road construction, building construction, and logging related activities in the watershed degrade aquatic substrate through increased erosion and sediment delivery (Rothrock et al. 1998). The loss of trees through timber harvest poses additional threats, since trees provide (1) shade that maintains lower water temperatures for larvae and (2) foraging and nighttime roosting areas for adults (Packauskas 2005).
Locally, cattle grazing and agriculture activities in the watershed pose the greatest threat to this species. Both the Malheur and Owyhee Basins support intense agricultural activities, including irrigated row crops, rangeland, and confined animal feeding operations (CAFOs) (Cude 2008). Degraded water quality, including high levels of total phosphates, biochemical oxygen demand, ammonia, nitrate nitrogen, and fecal coliform bacteria, has been reported in both of these rivers, and irrigation withdrawals, fertilizers and animal waste breakdown products have been identified as the major sources of contamination (Cude 2008). While the upper course of the John Day River has protection under two important river preservation programs (the National Wild and Scenic Rivers Act and the Oregon Scenic Waterways Act), the lower course, including stretches where this species has been found, is used for crop irrigation and ranching (BLM 2008). De-watering of aquatic systems can have dramatic impact on habitat and communities by decreasing water depth, increasing sedimentation, and altering water temperature and chemistry (reviewed in Dewson et al. 2007). Grazing by livestock not only reduces the amount of vegetation available for perching and emerging, but also has deleterious impacts on water quality, including increases in nutrient levels due to introduction of livestock waste material into waters, and increases in temperature, sediment, and turbidity due to trampling and bank alteration (Agouridis et al. 2005, reviewed in Mazzacano and Black 2008). The soils in this species’ habitat, including both the lower Malheur Basin and lower Owyhee Basin, are fine-grained flood plain deposits, prone to erosion, and aggravated in some areas by livestock and poor farming practices (Cude 2008). Chemical pollution has been recognized as a threat to members of this family (Paulson 2008, pers. comm.), and insecticides, herbicides, and other pollutants carried in agricultural run-off and wind drift may have serious consequences for the reproductive potential and long-term survival of this species.
Global climate change may further threaten the long-term survival of this species. Projected changes in this region include increased frequency and severity of seasonal flooding and droughts, reduced snowpack to feed river flow, increased siltation, and increased air and water temperatures (Field et al. 2007), all of which could impact this species’ habitat unfavorably. Moreover, since many aspects of odonate survival (e.g. development, phenology, immune function, pigmentation, and behavior) are sensitive to changes in temperature, global climate change is predicted to have serious consequences on this taxon (Hassall and Thompson 2008).
It is not known if disease and predation are serious threats to this species, but stocking of non-native fish species for commercial or recreational purposes could negatively impact population survival, since the larvae may not be adapted to co-exist with such predators.
Inventory: Since this species is known from many areas in Oregon but only a few limited sites in Washington, Washington surveys are more pressing at this time. Surveys for new populations should be concentrated in southern Washington, since central Washington represents the extreme northwestern edge of this species’ range. Since population size is important in evaluating the stability of a species at a given locality, abundance estimates for this species at new and recorded sites would assist future conservation efforts.
Management: All known sites and their associated watersheds should be protected from management practices that would adversely affect any aspect of the odonate life-cycle. Since the largest proportion of an odonate’s life is spent as an aquatic larva, protecting the larval stage is most critical for the species’ success (Packauskas 2005). Water quality and water levels should be maintained at known sites and in other potential habitat in Washington. Fish management should focus on retention of the native species with which the insect community is adapted to co-exist; non-native species stocking should be avoided or minimized. Adaptive land management practices, such as conserving and restoring riparian buffers around known aquatic habitats and fencing to exclude livestock, may help protect this species from the impacts of grazing and agriculture (Packauskas 2005).
Abbott, J.C. 2007. “Erpetogomphus compositus.” OdonataCentral: An online resource for the distribution and identification of Odonata. 2007. Texas Natural Science Center, The University of Texas at Austin 3 Oct. 2008 <http://www.odonatacentral.org/index.php/FieldGuideAction.get/id/46076>.
Agouridis, C.T., S. R. Workman, R. C. Warner, and G. D. Jennings. 2005. Livestock grazing management impacts on stream water quality: a review. Journal of the American Water Resources Association 41(3):591-606.
BLM. 2008. “John Day River Study” 28 Oct. 2008 <http://www.blm.gov/or/districts/prineville/plans/johndayriverstudy/>.
Cude, C. 2008. “Oregon Water Quality Index Report for the Malheur and Owyhee Basins.” Oregon Department of Environmental Quality 27 Oct. 2008
Dewson, Z. S., A. B. W. James, and R. G. Death. 2007. A review of the consequences of decreased flow for instream habitat and macroinvertebrates. Journal of the North American Benthological Society 26(3):401-415.
Field, C. B., L. D.Mortsch, M. Brklacich, D. L. Forbes, P. Kovacs, J. A. Patz, S. W. Running, and M.J. Scott. 2007. Chapter 14: North America. In Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. and Hanson, C.E., eds.). Cambridge University Press, Cambridge, UK. Available at: www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter14.pdf.
Hassall, C., and D.J. Thompson. 2008. The effects of environmental warming on Odonata: a review. International Journal of Odonatology 11(2):131-153.
Johnson, J. and S. Valley. 2005. The Odonata of Oregon. Bulletin of American Odonatology 8(4):101-122.
Mazzacano, C., and S. H. Black. 2008. Petition to emergency list Susan’s Purse-making Caddisfly (Ochrotrichia susanae) as an endangered species under the U.S. Endangered Species Act. 8 July 2008. Xerces Society for Invertebrate Conservation. 28 Oct. 2008. <https://xerces.org/Endangered/Xerces_Society_Susan%27s_caddisfly_petition_July_8_2008.pdf>
Merritt, R. W., K. W. Cummins, and M. B. Berg. 2008. An Introduction to the Aquatic Insects of North America. Fourth Edition. Kendall/Hunt Publishing Co., Dubuque, Iowa. 1158pp.
NatureServe. 2008. “Erpetogomphus compositus.” NatureServe Explorer: An online encyclopedia of life [web application]. Feb. 2008. Version 7.0. NatureServe, Arlington, Virginia. 6 Oct. 2008 <http://www.natureserve.org/explorer/>
Packauskas, R. J. “Hudsonian Emerald Dragonfly (Somatochlora hudsonica): a technical conservation assessment.” 24 Aug. 2007. USDA Forest Service, Rocky Mountain Region. 16 Oct. 2008 <http://www.fs.fed.us/r2/projects/scp/assessments/hudsonianemeralddragonfly.pdf>
Paulson, D. 1999. Dragonflies of Washington. Seattle Audubon Society, Seattle 31pp.
Paulson, D. 2007a. “Washington Odonata.” Slater Museum of Natural History. Oct. 2007. University of Pugut Sound. 6 Oct. 2008 <http://www.ups.edu/x7041.xml>.
Paulson, D. 2007b. “Field Key to Adult Washington Dragonflies (Odonata).” Slater Museum of Natural History. Jan. 2007. University of Pugut Sound. 2 Oct. 2008 <http://www.ups.edu/x6518.xml>.
Paulson, D. 2008. Personal communication: E-mail exchange with Sarah Foltz Jordan regarding Pacific Northwest odonates.
NatureServe. 2008. “Erpetogomphus compositus.” NatureServe Explorer: An online encyclopedia of life [web application]. Feb. 2008. Version 7.0. NatureServe, Arlington, Virginia. 6 Oct. 2008 <http://www.natureserve.org/explorer/>.
Rothrock, J. A., P. K. Barten, and G. L. Ingman. 1998. Land use and aquatic biointegrity in the Blackfoot River watershed, Montana. Journal of the American Water Resources Association 34(3):565-581.
Tennessen, K. 2007. Odonata Larvae of the Pacific Northwest: An Identification Manual. Created for use in a taxonomic workshop sponsored by the Xerces Society and held at Evergreen State College, Olympia, Washington, March 16-18, 2007.
Profile prepared by Sarah Foltz Jordan, The Xerces Society for Invertebrate Conservation.