- Scientific name: Somatochlora elongata
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Special Concern (MA Endangered Species Act)
Description
Male ski-tipped emerald
The ski-tipped emerald (Somatochlora elongata) is a large, slender insect of the order Odonata, suborder Anisoptera (the dragonflies), family Corduliidae (the emeralds). Most striped emeralds (genus Somatochlora) are large and dark with at least some iridescent green coloration, brilliant green eyes in the mature adults (brown in young individuals), and moderate pubescence (hairiness), especially on the thorax. The ski-tipped emerald thorax is an overall bronzy brown color with metallic green highlights and with a yellow anterior stripe and posterior spot. The face is yellow with two dark brown cross bands, with the forehead (frons) a shimmering metallic green. The large eyes, which meet at a seam on the top of the head, are brilliant green in mature adults. The long and slender abdomen is most narrow at the base, widening to segment 5 (dragonflies and damselflies have 10 abdominal segments) and then narrowing slightly towards the distal end. The abdomen is black with a metallic green luster with a yellow lateral spot on segment 2. The wings of this species are transparent and, as in all dragonflies and damselflies supported by a dense system of dark veins.
Adult male ski-tipped emeralds range from 52 to 56 mm (2 to 2.2 in) in length. Females measure 58 to 62 mm (2.3 to 2.4 in) in length. Both sexes are similar in coloration and body form. Final instar nymphs can range from 19 to 24mm (0.75 to 0.95 in) in length (Tennessen 2019).
Eleven species of striped emeralds have been recorded in Massachusetts and ski-tipped emerald can resemble several species. For adult identification, differences in size and the pattern and coloration on the thorax and abdomen can help distinguish species; however definitive identification requires examination of the male’s ski-shaped terminal abdominal appendages or checking for the female’s large triangle-shaped vulvar lamina or subgenital plate (see Lam 2024). Determination of these features usually require species in-hand accompanied by a hand lens or macro camera lens. The clamp-tipped emerald (S. tenebrosa), Williamson’s emerald (S. williamsonia) and incurvate emerald (S. incurvata) are species most like the ski-tipped emerald in overall size (larger) and appearance and can be reliably separated by male terminal appendage and female vulvar lamina shapes. Also, Williamson’s and incurvate emeralds possess yellowish lateral abdominal spots, absent in ski-tipped.
The nymphs and exuviae can be distinguished by characteristics as per the keys in Needham et al. (2000), Soltesz (1996), and Tennessen (2019).
Male (left) and female (right) ski-tipped emeralds.
Life cycle and behavior
Note, nymphs are present year-round.
As with other Odonates, ski-tipped emerald goes through aquatic egg and nymph life stages, and a terrestrial adult stage. The cryptic nymphs are predators, feeding on a wide variety of aquatic insects, small fish, and tadpoles. Nymphs undergo several molts (instars) for at least 2 years until they are ready to emerge as winged adults. Nymphs emerge up onto emergent vegetation, exposed banks, or tree trunks. When the nymph reaches a secure substrate, the adult begins to push itself out of the exoskeleton. As soon as the abdomen and wings are fully expanded, the adult takes its first flight. This maiden flight usually carries the individuals up into surrounding forest or other areas away from water, where they spend several days maturing and feeding and are somewhat protected from predation and inclement weather. Ski-tipped emeralds can be found in fields and forest clearings foraging on small aerial insects, such as flies and mosquitoes, which are consumed while flying. The species is known to join feeding swarms with mosaic darners and other striped emeralds at dawn and dusk. When not feeding, ski-tipped emeralds rest hanging vertically or perch obliquely from tree or shrub branches. After about a week, adult coloration is acquired, and the dragonfly becomes sexually mature before returning to the breeding habitat to initiate mating.
Breeding in Massachusetts probably occurs from mid-July through August, as in other regions where this species occurs. Males patrol up and down stream banks and beaver channels, usually no more than two feet above the surface of the water in search of females. A joined male-female pair quickly flies off into the surrounding upland habitat to mate.
Following mating, oviposition (egg laying) occurs. Females of the genus Somatochlora oviposit alone and deposit their eggs directly into the substrate by tapping the tip of the abdomen on its surface. ski-tipped emerald females will cruise low and erratically around a small area near the bank of the stream, intermittently tapping the surface of the water and the surface of bank often covered with mosses. They tap the bank and then the water, going back and forth continuously possibly to wash their ovipositor. In Massachusetts, females of the ski-tipped emerald have been seen ovipositing in backwater channels, though elsewhere they have been found ovipositing in sections of rapids of streams.
Ski-tipped emerald adults first appear in late June, peak in July and August, and are on the wing into early September.
Distribution and abundance
The ski-tipped emerald is distributed from the Maritime Provinces west to Ontario and south to Minnesota, Michigan, and Pennsylvania, and sparsely through Appalachian Mountains of North Carolina and Georgia. In New England, this species is found in Maine, New Hampshire, Vermont, and Massachusetts. Within Massachusetts, the ski-tipped emerald has been observed in north-central and western portions of the state, specifically in the Miller’s, Chicopee, Connecticut, Deerfield, Westfield, and Hoosic watersheds. Ski-tipped emeralds are typically found in low abundance but can be found in higher abundances at several sites including observed oviposition and sampled tenerals (recently molted) that indicate potential breeding wetlands.
The ski-tipped emerald is listed as a species of special concern in Massachusetts. As with all species listed in Massachusetts, individuals of the species are protected from take (picking, collecting, killing, etc.) and sale under the Massachusetts Endangered Species Act.
Distribution in Massachusetts.
1999-2024
Based on records in the Natural Heritage Database.
Habitat
In Massachusetts, the ski-tipped emerald has been found inhabiting small to medium-sized streams flowing through various wetland habitats at higher elevations and found higher in watersheds. Such streams may have a moderate or very sluggish flow and dense or little emergent vegetation. At several sites, ski-tipped emeralds have been found patrolling and ovipositing at the swelling of streams created by beaver dams. Elsewhere in its range, the ski-tipped emerald can occasionally inhabit highly vegetated ponds.
Healthy habitats are vital for supporting native wildlife and plants. Explore habitats and learn about conservation and restoration in Massachusetts.
Typical beaver wetland habitat for ski-tipped emerald.
Threats
Threats to ski-tipped emerald include degradation to water quality from road run-off like salt, discharge of industrial and chemical pollutants, and loss of upland and riparian forests also needed for adult development. Ski-tipped emerald may also be vulnerable to anthropogenically-induced streamflow alteration. Warmer water temperatures and more severe drought via climate change may pose a threat for ski-tipped emerald persistence in Massachusetts as it’s a relatively high elevational species and may require cooler water temperatures to complete its life cycle.
Conservation
Survey and monitoring
Surveys should target known sites and new streams and wetlands to inform ski-tipped emerald occupancy and population status in Massachusetts. Surveys for adults are likely to be more effective for detection compared to nymph or exuvia as this life stage is extremely difficult to find. Adult surveys should target breeding and feeding habitats, including swarms, where detection might be most probable. Multiple site visits (e.g., ≥3) are likely required to detect this species because of its rarity and the difficulty to capture by net or camera. Sites with breeding evidence should be monitored every 5 years to document changes in occupancy and habitat conditions. Sites without breeding evidence require additional survey effort to conform breeding and nymphal habitat. Suitable stream and wetland habitat likely exists across the landscape as more sites have been identified in recent years. Effort should be devoted to surveys in new breeding and potential sink sites to further update ski-tipped emerald status in Massachusetts.
Management
Upland and wetland protection to maintain water quality and quantity is critical for the conservation of ski-tipped emerald. Protection of forested upland borders of these river systems are critical in maintaining suitable water quality and are critical for feeding, resting, and maturation. Development of these areas should be discouraged, and the preservation of remaining undeveloped uplands should be a priority. Alternatives to commonly applied road salts should be tested to minimize freshwater salinization.
Research needs
Research effort is needed to estimate occupancy and detection rates for this species as it likely inhabits other sites not previously surveyed and species detection is likely low. Further refinement is needed to identify species habitat requirements including flow regimes as this species seems to occupy a range of flows from streams to beaver backwaters. Species distribution models coupled with climate change projections are needed to help assess future species risk and identification of climate-resistant stream and wetland sites.
References
Dunkle, Sidney W. Dragonflies Through Binoculars. Oxford University Press, 2000.
Lam, E. Dragonflies of North America. Princeton NJ: Princeton University Press, 2024.
Needham, J.G., M.J. Westfall, Jr., and M.L. May. Dragonflies of North America. Scientific Publishers, 2000.
Nikula, B., J.L. Ryan, and M.R. Burne. A Field Guide to the Dragonflies and Damselflies of Massachusetts. 2nd ed. Massachusetts Natural Heritage and Endangered Species Program, 2007.
Paulson, D. Dragonflies and Damselflies of the East. Princeton NJ: Princeton University Press, 2011.
Soltesz, K. Identification Keys to Northeastern Anisoptera Larvae. Center for Conservation and Biodiversity, University of Connecticut, 1996.
Tennessen, K. Dragonfly Nymphs of North America: An identification guide. Springer, 2019.
Walker, E.M., and P.S. Corbet. 1975. The Odonata of Canada and Alaska, Vol. III. University of Toronto Press.
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| Date published: | March 6, 2025 |
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