Blue Dasher dragonfly (male, obelisking)

The following photographs show a Blue Dasher dragonfly (Pachydiplax longipennis) spotted along the boardwalk in the central wetland area at Huntley Meadows Park. This individual is a male, as indicated by its blue coloration and the terminal appendages at the end of its abdomen.

Male dragonflies have three terminal appendages, called “claspers,” including a pair of upper appendages called “cerci” and one lower appendage called an “epiproct.” The Blue Dasher’s cerci are black and are visible in all photos; its epiproct is tan and is visible in Photos 3-4. The male dragonfly’s claspers are used to grab and hold female dragonflies during mating.

The black nodules on the underside of the dragonfly’s thorax, shown clearly in Photo 1, are parasitic water mites.

Water mites (Family Arrenuridae) are a common still-water odonate parasite. They hatch from eggs laid underwater and the larva are free swimming. They seek then attach themselves to odonate larva and when the odonate larva emerges to molt into an adult, the mites transfer to the teneral dragonfly or damselfly. The mites continue to feed on the odonate’s fluids while the dragonfly/damselfly matures. When the odonate returns to water to reproduce, the mites drop back into the water where they continue to develop, undergoing a series of molts, feed on other underwater creatures, mate, and lay eggs. Source Credit: Ed Lam, author and illustrator of Damselflies of the Northeast.

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Some dragonflies, such as Blue Dasher, regulate their body temperature by perching in the “obelisk position”: the tip of the dragonfly’s abdomen is pointed toward the Sun, minimizing the surface area of the body exposed to direct heating by the Sun’s rays, thereby avoiding overheating.

Copyright © 2012 Walter Sanford. All rights reserved. www.wsanford.com

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One Response to “Blue Dasher dragonfly (male, obelisking)”

  1. Parasitic gall wasps | walter sanford's photoblog Says:

    […] Blue Dasher dragonfly (male, obelisking) – parasitic water mites on dragonfly thorax […]

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