The following slideshow features a couple of green Eastern Pondhawk dragonflies (Erythemis simplicicollis) spotted at two locations in Fairfax County, Virginia USA. Male Eastern Pondhawks are blue and females are green so these two dragonflies must be females, right? In a word, wrong.
Do you see any difference between the two dragonflies? The dragonfly shown in Slide 1 is a mature female Eastern Pondhawk; Slide 2 shows an immature male. Look closely at the tip of the abdomen for both dragonflies: see a full-size version of Slide 1; and Slide 2. Notice the differences between male- and female terminal appendages, as shown in the following composite image: male appendages are shown in the background photo; female appendages are shown in the inset photo.
Immature male (background photo) | Mature female (inset photo)
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”). Female dragonflies have a pair of cerci (superior appendages) that have little or no function.
Adult Eastern Pondhawk dragonflies exhibit sexual dimorphism: mature males are covered by blue pruinescence; females are green. The male Eastern Pondhawk’s green face distinguishes it from other similar-looking blue dragonflies. The following specimen was spotted at Accotink Bay Wildlife Refuge.
Some species of dragonflies do not exhibit sexual dimorphism. Terminal appendages may be used to differentiate males and females for many types of dragonflies, such as Stream Cruisers (Didymops transversa).
Related Resources: Odonate Terminal Appendages.
Copyright © 2013 Walter Sanford. All rights reserved.