Some critters are very aptly named. Others, well, it can get a little confusing. Case in point, the Ebony Jewelwing.
Now, everything in that name is apropos: ebony? the wings are jet black; jewel? the abdomen is a jewel-like iridescent green; wings? yep, four of them.
But the wings are ebony, not jewel-like, and the rest of the insect is jewel-like, not ebony. As monikers go, it’s all inside out.
All that aside, the Ebony Jewelwing (Calopteryx maculata) is a beautiful little critter, and it is near the top of my list of “bugs every Pennsylvania school kid should know.” Starting in late May and running through until September, they can be found feeding along just about any clean stream in the area.
They are unmistakable. There are several less-common species of Calopteryx in the State, but none combine the totally black wings and solidly bright greenish-blue body of the Ebony.
I mentioned totally black wings, and that is not entirely true; the female has a very diagnostic white spot (stigma) on the tip of her forewing.1 The female is a duller, brownish, grayish creature.
Males newly emerged from their larval state can be told by their red eyes.
The males spend a lot of time whirling their wings about—apparently that is alluring to lady jewelwings—and dogfighting with each other over females and territory.
Once a female is found, mating ensues and then the female dips much—and sometimes all—of herself underwater to lay her eggs, usually on submerged vegetation. Males often “fly cover” over the female as she lays her eggs.
I have often noticed that some males seem to look more bluish than greenish. I always assumed that this was a matter of the angle of the light.
Well, that’s sorta right…but mostly wrong.
According to Fitzstephens and Getty of the Kellogg Biological Station and Department of Zoology at Michigan State, it actually has to do with how fat the males are.
And amongst the Ebony Jewelwings, the fat guy gets the girl. 2
In sum: “younger males challenge and displace older males from mating territories. Fatter males tend to win fights.” 3
Okay, damselflies, at their most obese, are pretty skinny. How can one tell a “fat” damselfly from a “thin” damselfly?
Well, for those with a discerning eye, the fat males are more bluish-green than the emerald-green skinny males: “Males are a strikingly iridescent blue-green colour, resulting from a multilayer constructive interference reflector system in the epicuticle.“ 4
In short, light reflects from multiple reflective layers beneath the outer hide of the damselfly.
“In fatter males the lamellae are more compressed and the peak reflectance is at shorter wavelengths (blue).”
Leaner, greener males have greater spacing between lamellae and reflect longer wavelengths.” 5
In fat fellows, the fat pushes the layer closer together, causing a blue reflection; otherwise, the layers reflect green.
So head out to your nearest clean running stream and keep an eye out for Ebony Jewelwings, and when you find them, see if you can pick the winners from the losers.
Fat and blue
Gets to woo.
Green and thin?
They cannot win.
- That white stigma is the reason for the Latin specific name “maculata,” which simply means spotted—hence immaculate, without spot.
- I have to admit, that warms the cockles of my chubby little heart.
- Fitzstephens, DM, Getty T. “Colour, fat and social status in male damselflies, Calopteryx maculate,” Animal Behaviour. 2000 Dec; 60(6):851-855.
- ibid.
- ibid.