Imperfect and Tense: Dragonfl-eyes

Sunday 8 October 2017

Dragonfl-eyes

Dragonflies and damselflies have amazing eyes, especially the former, with their huge, almost wrap-around, pair of peepers. Their compound eyes can be comprised of as many as 30,000 facets, known as ommatidia, which give them an almost 360 degree field of view.

A male Southern Hawker

This is because each facet points in a slightly different direction, but the insect processes the partially-overlapping images to create near-surround vision. If that wasn't impressive enough, dragonflies have many more types of light-sensitive proteins, opsins, in their eyes than compared to humans. We have three, so are tri-chromatic, whereas some insects have quadruple that and some dragonflies have as many as thirty. This allows them to distinguish many more colours than we can, and they are also able to detect in the ultraviolet part of the spectrum, as well as polarised light.

Different portions of a dragon or damsel eye may be tuned to certain frequencies of light, so that when we look at the insect, its eyes seem to be of two, or more, colours.

A male Red-veined Darter, sadly deceased. From the top, its eyes are brown.

Whilst from below, they're blue

But enough of the science.

Have you ever wondered why a dragonfly always appears to be looking at you, no matter where you are in relation to it? OK, technically, it is always looking at you, what with all the 360 whatnot going on, but take another look at the Southern Hawker at the top of the blogpost. Do you notice anything?

Yep, it looks like they have pupils, even though we know that they don't possess eyes like ours. I think this is due to the absence of light being reflected back out from those facets which are facing us, which makes them appear black and gives the 'pupil' effect.

And because of the wrap-around malarkey, wherever we are in relation to the insect, this will happen. No matter whether we're in front...