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Identifying the ebony jewelwing

By Bill Dunson

 

A trick to learning names of new critters such as butterflies, dragonflies and damselflies is to concentrate on identifying a few common species first.

 

So the damselfly of the week for you to learn is the strikingly beautiful ebony jewelwing found throughout eastern North America. Not only is it common along small streams, it is also found in woods openings, it flies slowly and alights often, and it is distinctively colored. However, you need to know that the female and male look different, and the male's brilliant colors can vary.

 

Both sexes have broad black wings but the female has white spots on the tips. The female's body is dark and the male is either a brilliant metallic blue or green. The male does not actually change color but can appear blue or green depending on the direction of the light and the angle of view.

In other words this is a structural color, a common but little appreciated phenomenon by which the prism-like surface of the body refracts light. There is no pigment present that imparts color. Another good example is the throat of the male ruby-throated hummingbird, which may appear as red or black.

 

Now why does this tiny insect male have such a gorgeous coloration? The most likely explanations are advertisement by the male to defend its territory, to attract a female and to ward off avian predators (assuming it is distasteful). The slow flight of the male and the showy nature of its black wings and metallic body certainly indicate that it must be protected from birds.

 

So keep an eye out for this amazing example of insect beauty and natural adaptation.

 

Bill Dunson is a retired professor of biology from Pennsylvania State University who grew up in Georgia. He now lives summers on a farm in southwestern Virginia and winters in Englewood, Fla.






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