Auricles—Mystery Structure

The previous post, on the Columbia Clubtail, brought to mind an enigmatic set of structures of male dragonflies referred to as the auricles. The reason for the name is that the shape of auricles in some species is vaguely ear shaped. The function of the auricles is unknown at the moment, though the best guess is that they may assist the female as she tries to find the hookup point for mating.

Be that as it may, the auricles on some species are quite striking in shape and color. One such case is the Columbia Clubtail. The next two photos point out the auricles on a male Columbia Clubtail:





The auricles in this species are bright yellow, contrasting with the pruinose blue abdomen, and shaped like little tennis balls.

Here's another clubtail species, the Pacific Clubtail, which also has prominent yellow auricles.





Closely related to the clubtails is the Grappletail—also with prominent yellow auricles:





In darners, the auricles are more ear shaped, and not quite as prominent—though they do have a nice blue color. Here's an example in the Shadow Darner:





Here's another view, this time in a Paddle-tailed Darner:





Next is a view of the underside of dead Paddle-tailed Darner we found at Cranberry Lake.





Notice the little "hooks" along the edge of the auricles. What is their purpose?

In contrast, here is a similar view of a female darner, showing the lack of auricles:



All in all, the auricles are a mysterious feature of male dragonflies. Maybe one of these days we'll get to see these structures in action—that would be fun.