Dragonflies and Damselflies -- the Delicate, Daring Aerialists of Dyke Marsh
Virginia zoologist reports on survey.
Presenting his 2011 survey of the dragonflies and damselflies of the Dyke Marsh Wildlife Preserve, zoologist Chris Hobson told the Friends of Dyke Marsh Wednesday night that "the abundance is unbelievable."
For example, Hobson saw 5,000 of one species in one day and 1,000 of another during a short paddling trip. He found 16 species in the preserve on a four-day survey between April and September 2011, and four more have been identified in the preserve by Edd Barrows, a Georgetown University entomologist.
In Virginia, 194 species have been identified. The more varied the habitat, the more species are likely to be seen, Hobson said, explaining that a survey is a "snapshot."
He opened with a tutorial on odonata, the order encompassing dragonflies and damselflies. These insects have two pairs of wings and three pairs of legs, among other characteristics.
Dragonflies typically spread their wings to their sides, and their eyes are not separated. Damselflies are smaller; they usually hold their wings together over their abdomen, and their eyes are separated. To identify specific species, experts study their wings, wing patterns, colors, tail, thorax, abdomen, genitalia and other features, sometimes under a microscope. Some have bright, lustrous hues and diaphanous wings.
Dragonflies and damselflies are found around rivers, wetlands, seeps, bogs, springs, streams, ponds and lakes because their larvae, known as nymphs, are aquatic. Adults can be from half an inch to 5 inches long.
Hobson offered a few intriguing facts about odonates, his favorite invertebrate:
- Some “hang out” in noxious vegetation like stinging nettle and poison ivy.
- During mating, one species contorts into a "wheel" position, the female arching in a circle to connect to the male genitalia.
- Some are very adaptable. "Some species will breed in the bed of a truck," he quipped.
- They might bite if you catch them. "The big ones can pinch," Hobson said. "It’s like a mouse bite."
- Some species migrate south and return to Virginia in the spring.
They are "voracious predators," Hobson said. "They’ll eat anything they can catch and chew. Some are cannibalistic. They eat their brethren."
The months from April to November are the best time of year to see them. They zoom around, "patrol," establish territories and rest on vegetation. Hobson, who described their reproductive behavior as "fascinating," added, "It’s the wild west out there."
Hobson showed pictures and described the characteristics and behavior of many Dyke Marsh and Virginia species with provocative names like Halloween pennant, Prince baskettail, black saddlebags, common green darner, 12-spotted skimmer and russet-tipped clubtail. In Dyke Marsh, the most common species are the Eastern amberwing and the Needham’s skimmer.
The Friends of Dyke Marsh funded the survey. Hobson will share the data with the group and the National Park Service, the federal agency that owns and manages Dyke Marsh. Hobson works for the Virginia Natural Heritage Program in the Department of Conservation and Recreation.