Of Wings and Stigmata

Found the remains of a dragonfly on a Brooklyn sidewalk recently. Possibly a Common Green Darner, one of our most common species. One of the hind wings was still in pretty good shape.Pretty good, but at 40X showing some wear and tear. These two shots are hand-held through the microscope, so not as great as I’d like them, but certainly passable. And the leading edge. I was surprised to see how rough it looks, with regularly spaced thorn-like structures. But I shouldn’t have been. We think of the aerodynamic as streamlined, but this is old school thinking, from the Art Deco in Space, a.k.a. Jetsons, Era. We now know, from things like bird feathers, that a rough surface actually works better for flight.

The dark yellowish bit here the pterostigma, sometimes called simply the stigma, and yes, stigmata in the plural. (See first image for location: on front edge of the upper left). This is a thickened, pigmented cell. A number of other insects have these, but they are most obvious on dragonflies, some of our biggest-winged insects. The stigmata have greater mass than similar-sized sections of the wing. They seem to be a kind of ballast, helping with flight stabilization. Odonates are extraordinary fliers. See here for more detail: “By passive, inertial, pitch angle control, the pterostigma probably makes the wing beat more efficient in slow and hovering flight of small insects, while its raising of the critical flight speeds probably is of more importance to larger insects.”

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