Somatochlora williamsoni Walker, 1907
Williamson's Emerald
NatureServe Global Rank: G5
Virginia State Rank: SH
VA DGIF Tier: IV
Federal Legal Status: None
Virginia Legal Status: None
Description: Williamson's Emerald is large at 2.3 inches long. The face is blackish with dull yellow-orange sides. The thorax is brown and metallic green. The abdomen is black with faint pale rings at the base of the abdominal segment S3, and the female has orange-brown spots at the base of S4-S8, on the ventral side. Male cerci are straight in the side view and curling up at the tips, hairy above. The female has a very sharply pointed subgenital plate that projects at a right angle from the abdomen and often has yellow tinted wings.
Similar species: In Virginia Williamson's Emerald is similar only to the Clamp-tipped Emerald (Somatochlora tenebrosa), which is more brightly colored.
North American Range: The Williamson's Emerald is a northern species that ranges around the Great Lakes states and southern Canada, east across southern Canada and the New England states. There is a single population found well outside this range in Virginia and another in West Virginia.
VA Observations by Locality: Highland
Flight season and broods: Not exactly known, but presumably May through July.
Aquatic Habitat: Williamson's Emerald prefers slower forest streams or clear-sand or wave washed lake shores.
Behavior and Ecology: The Williamson's Emerald hunts high in the air along woodland edges and can be found in feeding swarms in the morning and evening. They fly lower while in the shade. Males patrol at knee to waist height along streams and lake edges. Females oviposit above the water line on wet, muddy banks and apparently clean the ovipositor by dipping it into the nearby water.
Population trend and potential threats: Williamson's Emerald may be negatively impacted by poor water quality and habitat degradation.
Management practices: Populations should be monitored and habitats preserved.
References: Bangma, J. 2003. The Dragonflies and Damselflies of New Jersey. http://njodes.com/Speciesaccts/species.asp . Accessed: 4/8/2013
Dunkle, Sydney W. 2000. Dragonflies Through Binoculars: A Field Guide to Dragonflies of North America. Oxford University Press, New York, NY. 266 pp.
Paulson, Dennis. 2011. Dragonflies and Damselflies of the East. Princeton University Press, Princeton, NJ. 530 pp.