First they transform from aquatic macro-invertebrates into flying insects. And then they perform flight rituals that include snagging a meal and mating. Dragonflies, as many of you know, absolutely amaze me.
And today, that amazement reached a new level.
For today, I took a closer look at the compound eyes of my favorite insects. I know from reading and listening to others, that large dragonfly eyes consist of 30,000 lenses . . .
each an individual light-sensing structure, but . . .
whenever I study them in situ, though I’m completely wowed by their colors . . .
and the arrangement of eyes that helps with identification . . .
always it seems, the eyes are splotchy with some areas glowing and others a slightly different hue.
Do you see what I mean? Dark blue-gray above and almost a streak of whiteness in this Ring-tailed Emerald, followed by another shade of blue-gray below?
And have you ever noticed that dragonfly eyes wrap around almost the entire head? The thing is, an insect can’t move its eyes like we can so it needs a different adaptation . . .
in the form of hexagon-shaped structures that sense light and are known as the ommatidium or those 30,000 lenses per eye. Can you see the hexagons? Each ommatidium is much longer than it is wide. The ommatidium narrows as it leads to the brain as I’ve learned from How Insects Work by Marianne Taylor. She states: “Each ommatidium is topped with a cornea and a crystalline pseudocone, which acts as a focusing lens, directing light into the rhabdom, a long, narrow, and transparent structure at the center of the ommatidium. It contains photosensitive pigments that respond to certain wavelengths of light. The rhabdom is formed by the combined inner parts of (usually) eight specialize nerve cells–photoreceptors. When the rhabdom’s pigments undergo chemical change in response to light, these cells send a nerve impulse to the brain. The ommatidium also contains six pigment cells, which absorb light that strikes the cornea at an indirect angle. This ensures that the photoreceptors only receive light that passes through the cornea directly . . . what the compound eye “sees” is, as far as we can tell, a scene formed by an array of colored specks (including, in some cases, ultraviolet “color”), each speck contributed by an individual ommatidium. In dragonflies, there are enough specks to form a detailed picture, but in insects with fewer ommatidia the compound image has little detail.”
Here’s a look inside the head of a dragonfly from a specimen I’d collected after it died two years ago. What I didn’t realize until today was that the head had fallen off the thorax because its such a delicate creature once dried. But . . . that was great news because it gave me an opportunity to see more. I thought you might like to do the same. Though we can’t really get inside a dragonfly’s head, we can certainly enjoy the view of the backside.
Worth a wonder!
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