More Black-shouldered Spinyleg dragonflies

Another female and male Black-shouldered Spinyleg dragonfly (Dromogomphus spinosus) were spotted during a follow-up photowalk along the Potomac River at Riverbend Park.

Female and male Black-shouldered Spinyleg are somewhat similar in appearance. Terminal appendages, the shape of their hind wings, and the relative size of their club are good field markers to differentiate specimens by gender.

Female

The first individual is a female, as indicated by her terminal appendages. Female dragonflies have a pair of cerci (superior appendages) that have little or no function.

A Black-shouldered Spinyleg dragonfly (Dromogomphus spinosus) spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a female.

08 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (female)

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

The preceding dorsal view of the dragonfly shows its hind wings are rounded near the body, a good field marker for female clubtail dragonflies. In contrast, the hind wings of male clubtails are “indented.” Also notice the female “club” is slightly smaller than the male club, as shown in the following photos.

A Black-shouldered Spinyleg dragonfly (Dromogomphus spinosus) spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a female.

08 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (female)

A Black-shouldered Spinyleg dragonfly (Dromogomphus spinosus) spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a female.

08 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (female)

A Black-shouldered Spinyleg dragonfly (Dromogomphus spinosus) spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a female.

08 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (female)

Male

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”).

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

Although the preceding photo seems to show four terminal appendages, do not be misled! The epiproct for Black-shouldered Spinyleg is essentially a wide plate with two prongs.

Notice the male’s middle leg (on the right side, facing forward) is shorter than either its front- or hind leg. I’m not sure whether the middle leg is malformed, or the result of an injury. Whatever the cause, it might explain why the dragonfly was especially skittish.

Related Resources: Digital Dragonflies, presenting high-resolution digital scans of living dragonflies.

  • Genus Dromogomphus | Dromogomphus spinosus | Black-shouldered Spinyleg | male | top view
  • Genus Dromogomphus | Dromogomphus spinosus | Black-shouldered Spinyleg | male | side view

Copyright © 2016 Walter Sanford. All rights reserved.

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6 Responses to “More Black-shouldered Spinyleg dragonflies”

  1. Life-list additions in 2016 | walter sanford's photoblog Says:

    […] 04 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (male) […]

  2. Top 10 Photos of 2016 | walter sanford's photoblog Says:

    […] 08 AUG 2016 | Riverbend Park | Black-shouldered Spinyleg (female) […]

  3. Another record shot | walter sanford's photoblog Says:

    […] Boat Landing, Cumberland County, Virginia USA. This individual is a female, as indicated by her terminal appendages and rounded hind […]

  4. Black-shouldered Spinyleg (male) | walter sanford's photoblog Says:

    […] was spotted recently along a rocky stream in Fairfax County, Virginia USA. This individual is a male, as indicated by his terminal appendages and “indented” hind […]

  5. Black-shouldered Spinyleg (female) | walter sanford's photoblog Says:

    […] was spotted recently along a rocky stream in Fairfax County, Virginia USA. This individual is a female, as indicated by her terminal appendages and rounded hind […]

  6. Black-shouldered Spinyleg (males) | walter sanford's photoblog Says:

    […] spinosus) were spotted recently in Fairfax County, Virginia USA. All of these individuals are male, as indicated by their terminal appendages and “indented” hind […]

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