SOURCE: Arlington County Government
Theo nguồn tin trên trang mạng của Quận Arlington ở tiểu bang Virginia
If April showers bring May flowers, then you could say July showers bring … dragonflies.
August 23, 2018
It’s not just your imagination — you really have been seeing more dragonflies in and around Arlington County this summer.
“In general, more rain does result in more dragonflies, and their damselfly cousins,” says Alonso Abugattas, Natural Resources Manager for Arlington County.
It’s hardly news, but this has been a particularity wet summer. In fact, July was the fourth-wettest July ever; following nearly 10 inches of rain in July, our neighbors in D.C. are closing in on a typical year’s worth of rain (and it’s only August); Reagan National Airport got drenched with 2.5 inches of rain in just 42 minutes on July 17. Use whichever stat you prefer, but the upshot is this: it’s prime breeding ground for dragonflies.
“This is generally true due to a couple of factors. First of all, all Odonates (from Odonata, the order of predatory insects made up of dragonflies and damselflies) start off life in the water, some of the naiads or nymphs (what baby dragonflies and damselflies are called) hunting other aquatic creatures for several years underwater,” Abugattas explained. “So, more water obviously benefits them. But since as aquatic young they feed on other aquatic organisms, more water also means generally more aquatic food for them, as well.”
Abugattas notes that most dragonflies and damselflies (with their smaller, slimmer bodies) will hunt and mate near water sources. Though some, like the fairly uncommon Needham’s Skimmer and giant Swamp Darner, have been spotted in Arlington’s globally-rare Magnolia bog and meadow. (Arlington’s magnolia bog is one of only two-dozen known in the world.)
Many others hover over our playing fields, where they can feed on flying insects.
VIDEO: A Swamp Darner, one of our region’s largest dragonflies, oviposits eggs into a river birch log in Barcroft.
“Overall, these insects are of great benefit to people.”
Despite some folktales about dragonflies — previously, it had been believed they descended from dragons, would sew snakes together and could measure human souls — dragonflies are, in fact, helpful.
“They are actually extremely beneficial,” Abugattas said, “catching and eating many insect pests, with damselflies in particular eating mosquitoes. A couple of the big ones can give a little nip if you grab them, but only if you grab one. They do not go after people.”
Dragonflies also serve as an indicator of water quality, and are used as such during stream macroinvertebrate water samples.
If you’re interested in learning more, there’s a summary of the Dragonfly and Damselfly inventory report in the Wildlife of Arlington: A Natural Heritage Resource Inventory Technical Report. It also lists some of the best dragonfly observation sites, including Barcroft Park, Cherry Valley Park and Long Branch Nature Center.
Abugattas reports more than 28 species of dragonflies and 14 species of damselflies have been recorded in Arlington so far, “but we likely have many more species yet to be recorded.”
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https://newsroom.arlingtonva.us/release/dragonflies-damselflies-arlington/
