Friday, September 20, 2013

Dragonfly Eyes

The identity of this female meadowhawk eludes me. I suspect it is a White-faced, one of a trio of dragonfly species called “the troublesome three,” the females often being impossible to identify in the field (King). This photo shows dragonfly eyes.

The eyes are compound, consisting of some 28,000 photoreceptors, each with its own lens and nerve. Dragonflies can see in every direction at once, but see best where their receptors are densest. These clusters, called pseudo-pupils, are often dark. On their crowns, dragonflies also have several simple eyes that do not percieve images, but are sensitive to sudden changes in light or shadow (Taylor).

Scott King comments: "this is one place that Taylor got the facts wrong. The dorsal portion of the eye, a characteristic of many skimmers, and seen in your photograph as the maroon area on the top of the compound eye and more sensitive to short wavelengths of light, a specialization for locating prey against the blue sky. The pseudo-pupils has to do with the angle at which we are viewing the ommatidia, not their density."

1 comment:

  1. Dan, this is one place that Taylor got the facts wrong. The dorsal portion of the eye, a characteristic of many skimmers, and seen in your photograph as the maroon area on the top of the compound eye and more sensitive to short wavelengths of light, a specialization for locating prey against the blue sky. The pseudo-pupils has to do with the angle at which we are viewing the ommatidia, not their density. Scott

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