Aeshna multicolor

| 28 Comments

Photograph by David Cox.

Photography contest, Finalist.

Cox.Aeshna_multicolor.jpg

Aeshna multicolor – blue-eyed darner.

28 Comments

Is a “Darner”,the same as “Dragon Fly”? Is there another name for the other species?

latibulum said:

Is a “Darner”,the same as “Dragon Fly”? Is there another name for the other species?

It is a dragonfly, but there seem to be “darners” among the dragonflies, presumably because their bodies appear somewhat like darning needles.

Common names, there’s often no rhyme or reason to them.

Glen Davidson

latibulum said:

Is a “Darner”,the same as “Dragon Fly”? Is there another name for the other species?

“Darner” is the name for dragonflies of the family Aeshnidae. There are many other names for dragonflies of other families, and there are 11 families with around 3000 species, of which something over 400 are aeshnids.

Like all other flies, it’s of the devil, who is the Lord of the Flies.

Just Bob said:

Like all other flies, it’s of the devil, who is the Lord of the Flies.

After all, it is called the “dragon” fly!

What must it be like to have a more than hemispherical view of the world, with eyes that cover most of your head?

What an absolutely lovely photo. The work of a master who really knows how to use a superb camera. Congratulations!

Scott F said:

What must it be like to have a more than hemispherical view of the world, with eyes that cover most of your head?

The better to see your prey with, of course - a clear evolutionary advantage.

Scott F said:

What must it be like to have a more than hemispherical view of the world, with eyes that cover most of your head?

I’m sure it screws up distance sight horribly.…

david.starling.macmillan said:

Scott F said:

What must it be like to have a more than hemispherical view of the world, with eyes that cover most of your head?

I’m sure it screws up distance sight horribly.…

I’m not sure it would, and I don’t think it matters much. Insects’ compound eyes, even at that size, can’t resolve the world to the same level of detail that humans’ can anyway. The physics of optics won’t allow it. Here’s a neat site here that helps explain how insects like dragonflies see, and the benefits and limitations of their ocular anatomy.

Are dragonflies decapods? 6 legs plus 4 wings = 10 limbs?

Carl Drews said:

Are dragonflies decapods? 6 legs plus 4 wings = 10 limbs?

Bird wings are limbs (evolved from legs–same bones, which fuse), bat wings are limbs, and insect wings are not limbs. Insect wings likely evolved from gills.

To be sure, fins that evolved into legs may well have been something else once, too, so why is the “leg” what counts? Probably because the bones are typically so clearly “leg bones.” I assume that insect wings don’t reveal their gill origins (if correct) nearly so well, so aren’t hexapods/tetragills, which is cumbersome anyhow.

Then again, why are insects even hexapods, considering that their “legs” presumably aren’t homologous with vertebrate legs (there may be deep homologies, but I doubt any “true homology”). Probably convenience. After all, legged vertebrates are all tetrapods (snakes still develop some of the requisite bones), as far as I know (and we’re bipedal, while tetrapods), so why even bother unless you call some things hexapods, others octopods, and squids, decopods?

It’s not formal science, just wing-it science. They’ll still demand legs at some point for a (number)pod, though.

Glen Davidson

https://me.yahoo.com/a/JxVN0eQFqtmg[…]X_Zhn8#57cad said:

Insect wings likely evolved from gills.

Glen Davidson

Really? That’s cool. I have nothing more cogent to add.

Tetrapod constraints always make me think of origami, specifically the way that in (simple) origami folds, you are limited to four extremities based on the corners of the square you started with. I don’t know if anyone else thinks about that or if it just shows I’m weird (and definitely not a biologist, and not very good at origami either).

I wonder if the bit about the snake losing its legs in Genesis came from cutting open snakes and seeing the remnants of its limbs.…

But doesn’t “pod” mean foot, rather than limb?

david.starling.macmillan said:

I wonder if the bit about the snake losing its legs in Genesis came from cutting open snakes and seeing the remnants of its limbs.…

Possibly, people just expected it to have legs. Even if the idea of a vertebrate wasn’t expressed as such, it is not hard to imagine looking at a snake and expecting it to be more like a lizard than a worm.

callahanpb said:

david.starling.macmillan said:

I wonder if the bit about the snake losing its legs in Genesis came from cutting open snakes and seeing the remnants of its limbs.…

Possibly, people just expected it to have legs. Even if the idea of a vertebrate wasn’t expressed as such, it is not hard to imagine looking at a snake and expecting it to be more like a lizard than a worm.

Good point.

Yeah, the notion of it being more like a worm just wouldn’t have a leg to stand on.

When I was a kid, the prevailing mythology was that dragonflies would, given the opportunity, sew your eyes shut. They were much feared.

We would have called any small, slim dragonfly a “darning needle” – has “darner” replaced that term? A little Googling shows that “devil’s darning needle” refers to any dragonfly, but it seems that all dragonflies are not darners. I guess that is why we use scientific names, but I am curious about the use of “darning needle”: does it means any dragonfly or only certain species?

We always just called them dragonflies, but there was a prevailing belief that they would do something horrible. Bite, sting, whatever. I remember actually being lucky enough to catch one live and get a close look at its mouth moving. It was the fatter kind, not like the picture. My friends were definitely freaked out, and I released it fast. I am pretty sure I already knew they didn’t sting, as I’ve always been risk averse.

Note: I believe this actually happened to me, but it is so similar to a story Feynman tells about “darning needles” in his autobiography, that I’m seriously wondering.

ksplawn said:

david.starling.macmillan said:

Scott F said:

What must it be like to have a more than hemispherical view of the world, with eyes that cover most of your head?

I’m sure it screws up distance sight horribly.…

I’m not sure it would, and I don’t think it matters much. Insects’ compound eyes, even at that size, can’t resolve the world to the same level of detail that humans’ can anyway. The physics of optics won’t allow it. Here’s a neat site here that helps explain how insects like dragonflies see, and the benefits and limitations of their ocular anatomy.

That is a pretty good article; but I am not sure that it accounts for other types of neural processing that can improve resolution.

I worked for a number of years on the development of various types of imaging systems, including synthetic aperture imaging of ultrasonic echoes and various types of CCD imagers that work in the infrared. I developed a number of algorithms for improving the resolution of the images from ultrasonic echoes, and I did considerable theoretical and experimental work on the development of infrared CCD imaging devices. To my knowledge, some of that infrared CCD imaging work is still classified.

The resolution of an imaging system is not just restricted to the physical size of the receptors of an imaging system; so inferring the resolution from the physical size and arrangement of the receptors in not enough. One also has to take into account how the signals from the various elements of the array of sensors are processed within the neural network that interconnects them to each other and to the final interpretative system, such as a brain, to which the signals are sent.

For example, in synthetic aperture systems, a single sensor can be scanned over a large area and the signals from that sensor can be delayed and summed in such a way as to simulate a much larger aperture than that of the single sensor itself. The result is greatly improved spatial resolution. There are also additional processing techniques that can take into account the scattering characteristics of the objects being imaged; so resolution is not restricted to just the properties of the imaging system itself.

Even if one has an array of sensors that cover a much larger area than a single sensor, it is not enough to just look at the outputs of that array to try to estimate the resolution of the entire set of sensors. One also has to know about the delays and summing of the signals from the individual sensors in order to assess the resolution of the entire collection.

Many, if not all, of the shortcomings of an array can be overcome by appropriate delays and summing that occurs within the neural network of the imaging system. I have always wondered if the spatial and temporal resolution of compound eyes might not be even far superior to single eyes such as those found in fish and mammals.

I don’t know if any of the latest research on compound eyes of insects takes into account everything we know about the total imaging systems – including the neural networks interconnecting their parts - used by , say, the military or NASA today.

By the way, a flexible lens is not necessary for focusing; especially with an array of sensors. The focusing can occur by delaying and summing the signals from the various sensors in array. The closer the sensor is to the center of the array, the more delay one places on that sensor’s signal. The delays to sensor signals are such that they all arrive at a given node at the same time where they are then summed.

Furthermore, distance focusing is done by changing the delays in the neural work. In imaging systems that have to adapt very rapidly as the imaged scene changes, it is far more efficient to do the electrical delays rather than change the focusing mechanically. One can even tap into various parts of the delay lines of the neural network and have images that are in focus simultaneously at many distances.

So, in the case of a darting insect or a high velocity rocket, any imaging system it needs to navigate can respond much more quickly if the focusing and processing of the signals take place within the neural network rather than through some mechanical lens system. Speeds can be thousands to millions of times faster.

…a flying wonder that took a darn long time to evolve and learn to fly “strait”…!

How many species of dragonflies bite? In Michigan, there were 4 winged dragonflies, that looked like this, that sometimes (but rarely, would bite people like horseflies.

Henry J said:

But doesn’t “pod” mean foot, rather than limb?

Like in iFoot?

Can anyone with some experience comment on the recent story about a study of the rapid evolution of “color” in butterfly wings, due to artificial selection? “Color”, in this context, being the result of the reflective and refractive properties of the otherwise pigment-less insect wings. Sounds like a wonderful example of the power of evolution to cope with a changing environment.

But they’re still just butterflies, don’cha’no’.

KlausH said:

How many species of dragonflies bite? In Michigan, there were 4 winged dragonflies, that looked like this, that sometimes (but rarely, would bite people like horseflies.

None of them are really trying to bite you, and any of smaller ones won’t even hurt. The bigger ones have bigger jaws, and the amount of “damage” they can do tends to increase proportionately. But again, they’re not trying to bite and it’s pretty rare that they would even get the chance to do so unless you were holding in your hand or something.

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