Posts Tagged ‘obelisk position’

Return to terra firma

September 16, 2016

Several Blue-faced Meadowhawk dragonflies (Sympetrum ambiguum) were spotted near two vernal pools at a remote location in Huntley Meadows Park. All of these individuals are males, as indicated by their coloration and terminal appendages.

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

The next photo shows one of the males perching in the obelisk position.

Many dragonflies [perch in the] obelisk position to limit the amount of sunlight hitting their body and use their wings to shade their overheated thoracic flight muscles. Why not just find a shady spot? If he did he would relinquish his territory and that would reduce his chances for mating. Source Credit: Richard Orr, renowned expert on odonates of the mid-Atlantic region of the United States.

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

Regular readers of my photoblog know I’m fond of head-tilts in which the dragonfly seems to display some of its personality, especially when the individual is looking at me. I nicknamed this guy “Paleface” because his face is a lighter shade of turquoise than most male Blue-faced Meadowhawks.

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

The last three photographs were taken in a dry drainage ditch located near one of the vernal pools. According to the most recent U.S. Drought Monitor update, parts of the Washington, D.C. metropolitan region are “abnormally dry” — one classification category from “drought.”

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

12 SEP 2016 | HMP | Blue-faced Meadowhawk (male)

The Backstory: Teneral Blue-faced Meadowhawk dragonflies were observed at Huntley Meadows Park during late-May and early-June 2016, documented in Previews of coming attractions by Walter Sanford. (Hey, that’s me!) A pull quote from that blog post explains the title of this one.

Blue-faced Meadowhawk dragonflies are classified as a fall species of odonate. In the mid-Atlantic United States, meadowhawks seem to disappear for several months after they emerge during early summer and reappear during fall. Where do they go? No one knows for sure. I speculate Blue-faced Meadowhawks are an arboreal species of dragonfly that returns to the ground/water when it’s time to mate.

It must be time for Blue-faced Meadowhawks to mate, because they’ve returned to terra firma!

Related Resources:

Copyright © 2016 Walter Sanford. All rights reserved.

Advertisements

Cobra Clubtail claspers

May 19, 2016

All male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”) and a lower unpaired epiproct (“inferior appendage”).

A Cobra Clubtail dragonfly (Gomphurus vastus) was spotted at Riverbend Park, Fairfax County, Virginia USA. Two field markers indicate this individual is a male, as shown in the following annotated image: 1) it has three terminal appendages; and 2) its hind wings are slightly “indented.”

A Cobra Clubtail dragonfly (Gomphus vastus) spotted at Riverbend Park, Fairfax County, Virginia USA. This individual is a male.

16 MAY 2016 | Riverbend Park | Cobra Clubtail (male)

(See a full-size version of the original photo, without annotation.)

All male dragonflies have three terminal appendages, right? Look closely at the preceding annotated image. Notice there are four “prongs” at the posterior end of the abdomen. Cobra Clubtails feature a two-pronged epiproct. Just thought I should clarify any cognitive dissonance that may have been caused by looking at these images!

A Cobra Clubtail dragonfly (Gomphus vastus) spotted at Riverbend Park, Fairfax County, Virginia USA. This individual is a male.

16 MAY 2016 | Riverbend Park | Cobra Clubtail (male)

Notice the male’s abdomen is slightly more elevated in the preceding photo than in the annotated image.

Males perch on shore, or on rocks in rocky rivers, with abdomen elevated, then fly beats up and down. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 5952-5953). Princeton University Press. Kindle Edition.

Some species of dragonflies 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. Given the orientation of Cobra Clubtail relative to the Sun, I’m guessing this type of perching behavior is probably intended to mark territory and attract mates.

Editor’s Note: Female Cobra Clubtail dragonfly terminal appendages will be featured in a follow-up post: Cobra Clubtail dragonflies (females).

Copyright © 2016 Walter Sanford. All rights reserved.

Blue Dasher dragonfly (female, obelisking)

November 27, 2015

Seems like just yesterday Blue Dasher dragonflies (Pachydiplax longipennis) were everywhere. Now they’re nowhere to be found. (Heavy sigh.) It’s going to be a long winter!

This individual is a fresh-faced female, as indicated by her coloration and terminal appendages.

Some species of dragonflies, such as the Blue Dasher shown in this photo set, 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 © 2015 Walter Sanford. All rights reserved.

Thermoregulation

September 8, 2015

They’re back! Blue-faced Meadowhawk dragonflies (Sympetrum ambiguum), that is. Their recent reappearance is a sure sign that fall has arrived, summer-like warmth to the contrary.

This individual is a male, as indicated by its coloration and terminal appendages.

A Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a male.

06 SEP 2015 | HMP | Blue-faced Meadowhawk (male)

Some dragonflies, such as the Blue-faced Meadowhawk shown in the preceding photo, 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.

Related Resources:

Copyright © 2015 Walter Sanford. All rights reserved.

Parasitic water mites

July 8, 2015

Chiggers and ticks parasitize human odonate-hunters sometimes; water mites parasitize odonates sometimes. In my experience, some species of dragonflies seem to be more likely to be infested with water mites than others.

Lentic, slow moving water, ponds and temporary water are what mites need for their life cycle. The mites get onto late stage [odonate] nymphs, and then emerge with the nymph. As it ecloses the mites transfer to the adult damselfly, dragonfly. Life cycles of mite and host must be at stages where this can happen, so only certain species would probably be emerging at those times. Species that emerge earlier or later in the season probably wouldn’t have to deal with them. There’s more than one species of mite, so different species would emerge at different times. There is some reference in Corbet’s book [Corbet, Phillip S. (1962). A Biology of Dragonflies.] about some (grooming) species grooming themselves better, and knocking them off also, so they’ve evolved to attach to species where their life cycle can be completed. Some of these species disperse them well also. Nature is truly amazing! Source Credit: Stick LaPan, Northeast Odonata Facebook group.

Odonates and parasitic water mites are able to co-exist except in cases of extreme infestation, when parasitization can be fatal.

Halloween Pennant dragonfly (Celithemis eponina), spotted in a remote location at Huntley Meadows Park, has a mild infestation of black water mites. This individual is a female, as indicated by its coloration and terminal appendages.

A Halloween Pennant dragonfly (Celithemis eponina) spotted near Dogue Creek, Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a female with a mild infestation of black water mites.

29 JUN 2015 | Huntley Meadows Park | Halloween Pennant (female)

The next photo shows the same female with another water mite attached to the underside of its abdomen.

A Halloween Pennant dragonfly (Celithemis eponina) spotted near Dogue Creek, Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a female with a mild infestation of black water mites.

29 JUN 2015 | Huntley Meadows Park | Halloween Pennant (female)

Another Halloween Pennant dragonfly, spotted at the same remote location 12 days earlier, has an infestation of red water mites. This individual is an immature male, as indicated by its coloration (similar to a female) and terminal appendages.

A Halloween Pennant dragonfly (Celithemis eponina) spotted near Dogue Creek, Huntley Meadows Park, Fairfax County, Virginia USA. This individual is an immature male with a mild infestation of red water mites.

17 JUN 2015 | Huntley Meadows Park | Halloween Pennant (immature male)

Blue Dasher dragonfly (Pachydiplax longipennis), spotted along the boardwalk in the central wetland area at Huntley Meadows Park, has an infestation of black water mites. This individual is a male, as indicated by its blue coloration and terminal appendages. He is perching in the obelisk position, thought to be a method of thermoregulation.

Copyright © 2015 Walter Sanford. All rights reserved.

Blue Dasher dragonflies (immature males)

May 25, 2015

Blue Dasher dragonflies (Pachydiplax longipennis) display sexual dimorphism; terminal appendages may be used to differentiate immature males from females.

A Blue Dasher dragonfly (Pachydiplax longipennis) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a young male.

14 MAY 2015 | Huntley Meadows Park | Blue Dasher (immature male)

This individual is an immature male, as indicated by its red eye color, blue partial pruinescence, and terminal appendages. When male Blue Dashers mature, their eyes are blue-green and their abdomen is completely blue except for the black tip.

A Blue Dasher dragonfly (Pachydiplax longipennis) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a young male.

14 MAY 2015 | Huntley Meadows Park | Blue Dasher (immature male)

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.

A Blue Dasher dragonfly (Pachydiplax longipennis) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a young male.

14 MAY 2015 | Huntley Meadows Park | Blue Dasher (immature male)

Another immature male was spotted at the same location about a week later.

A Blue Dasher dragonfly (Pachydiplax longipennis) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a young male with a malformed wing.

22 MAY 2015 | Huntley Meadows Park | Blue Dasher (immature male)

Did you notice this individual has a malformed wing? A lot can go wrong when a dragonfly metamorphoses from a larva to an adult!

A Blue Dasher dragonfly (Pachydiplax longipennis) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This individual is a young male with a malformed wing.

22 MAY 2015 | Huntley Meadows Park | Blue Dasher (immature male)

Copyright © 2015 Walter Sanford. All rights reserved.

Anything but common

June 25, 2014

Common Sanddragon dragonflies (Progomphus obscurus) are anything but common.

Despite its name, this species is rare in Northern Virginia. Source Credit: Common Sanddragon, Dragonflies of Northern Virginia, by Kevin Munroe, Park Manager, Huntley Meadows Park.

Kevin goes on to cite Bull Run and Goose Creek, two streams where he has seen Common Sanddragons, and speculates they may be found at two other locations in Northern Virginia. Well, you can add a third location where sanddragons have been seen and it’s right in Kevin’s wheelhouse!

Mike Powell, a fellow amateur wildlife photographer and blogger, photographed a clubtail dragonfly at Huntley Meadows Park on 17 June 2014 that he was unable to identify. Mike’s description of the habitat where he saw the dragonfly piqued my curiosity, so I asked him to send me a photo of the unknown dragon. Turns out Mike discovered a Common Sanddragon — a new species of clubtail dragonfly for Huntley Meadows Park!

Mike volunteered to meet at the park on 20 June 2014 so that he could guide me to the location where he spotted the Common Sanddragon. After a LONG, DIFFICULT WALK to a VERY REMOTE location in the park, we spotted several sanddragons as soon as we reached our destination, including two mating pairs! The following photos show several males that I spotted during what turned out to be a very productive photowalk.

Common Sanddragon dragonfly (Progomphus obscurus)

They are usually seen along sandy shores, as their larvae are highly modified as sand burrowers. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Location 4833). Princeton University Press. Kindle Edition.

In this case, the sanddragons were found near sand deposits along a small stream that has carved a shallow channel in what appears to be a bed of iron-rich marine clay.

Huntley Meadows lies in a wet lowland carved by an ancient meander of the Potomac River. Source Credit: Huntley Meadows Park home page, Fairfax County Park Authority.

Common Sanddragon dragonfly (Progomphus obscurus)

Common Sanddragon dragonfly (Progomphus obscurus)

Common Sanddragon dragonfly (Progomphus obscurus)

The last photo in the set shows a male perching in a pose similar to the “obelisk position,” used by some dragonflies as a method of thermoregulation. Although sanddragons obelisk, especially at midday, the pose of this male sanddragon is probably intended to both attract females and communicate to other males, “This is my territory.”

Common Sanddragon dragonfly (Progomphus obscurus)

Editor’s Note: Please stay tuned for several upcoming posts featuring more photos of Common Sanddragon dragonflies, including two mating pairs, and two emergent sanddragons and their exuviaea (cast skins) — in short, a photo-documentary of most of the sanddragon life cycle!

Copyright © 2014 Walter Sanford. All rights reserved.

Blue Dasher dragonfly (male, obelisking)

July 29, 2012

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.

P1130070-rw2-ver3_apertureP1130070-rw2-ver2_apertureP1130074-rw2-ver3_apertureP1130075-rw2-ver3_aperture

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


%d bloggers like this: