- What are terminal appendages?
- Why are terminal appendages important field markers in dragonfly identification?
Let’s begin by answering the first question.
Male terminal appendages
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”). Male dragonfly terminal appendages don’t look exactly the same for all species of dragonflies, but their function is identical.
Can you identify the male’s three terminal appendages in the following photo? If necessary, then refer to the annotated image (shown above).
Female terminal appendages
Female dragonflies have a pair of cerci (superior appendages) that have little or no function.
Can you identify the female’s two terminal appendages in the following photo? If necessary, then refer to the annotated image (shown above).
Notice the differences between female- and male terminal appendages, as shown in the following composite image: female appendages are shown in the background photo; male appendages are shown in the inset photo. See a full-size version of the composite image for a clearer view of the side-by-side comparison of female/male terminal appendages. The difference is obvious, isn’t it?
Why are terminal appendages important field markers in dragonfly identification?
When you’re ready to move to the next level of dragonfly spotting (see “Step 2” of 5), from say the beginner level to the intermediate/advanced intermediate level, you must learn to identify terminal appendages in order to differentiate males and females of the same species.
It all comes down to sexual dimorphism: mature males and mature females are either identical/nearly identical in appearance; or mature males and mature females are different in appearance, especially their coloration.
- For those species of dragonflies that do not display sexual dimorphism, males and females are nearly identical in appearance except for their terminal appendages. For example, the male and female Painted Skimmer dragonflies (Libellula semifasciata), shown above, look similar.
- For many species that display sexual dimorphism, immature males appear similar to mature females. This is true for many members of the Skimmer Family of dragonflies, such as Great Blue Skimmer (Libellula vibrans) and Slaty Skimmer (Libellula incesta).
- More dragonfly terminal appendages [Blue-faced Meadowhawk]
- A sampler of male dragonfly claspers (Part 1)
- A sampler of male dragonfly claspers (Part 2)
- Odonate Terminal Appendages
Copyright © 2015 Walter Sanford. All rights reserved.
Tags: cerci, claspers, epiproct, female, Huntley Meadows Park, Libellula semifasciata, male, Painted Skimmer dragonfly, sexual dimorphism, Skimmer Family, terminal appendages, vernal pool, wildlife photography