The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note any observations you have made of the world around you. Rain, sun, wind...insects, birds, flowers...meteorites, rocks...seasonal changes...all are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
Dragons are exceedingly rare. I've only seen one once and I'm fairly sure the libations I had enjoyed earlier may have had something to do with it. My friends assure me this is the case and maintain that none of them saw anything. So where did this photo come from?
Dragonflies, on the other hand, are plentiful and, best of all, verifiable. Stand still in the tall grass or near a body of water and they'll come around to see if you're lunch. There is more cool stuff to know about dragonflies than could possibly be covered in one little bucket, but here are some highlights.
Dragonflies developed over 300 million years ago, long before mammals even existed. And they weren't the petite little flyers they are today. During the Paleozoic, dragonflies had wingspans of two to two and a half feet. It's been suggested that their huge size was due to an atmosphere with 50% more oxygen in it than it has today.
Imagine this guy with a 2.5 foot wingspan!
The order Odonata includes both dragonflies (the pic above is a 12-spotted dragonfly) and damselflies (the pic below I believe to be an American Bluet, a damselfly). As a group, they are referred to as odonates. Hie thee to Ye Olde Wiki for more details as my knowledge of phylogeny is not well-developed. ;)
The primary difference between the two types seems to be the way they hold their wings when they perch. Dragonflies hold theirs out at a 90 degree angle while damselflies hold them close to their bodies. However (there's always a however), a species damselfly exists which holds its wings out like a dragonfly. It is the aptly named spreadwing damselfly. The one below is the slender spreadwing, Lestes rectangularis.
A second difference is the placement of their eyes. Dragonfly eyes touch each other, while damselfly eyes are separate. The two pictures above are good illustrations of the damselflies' eyes (say that ten times fast and I'll buy you a drink!). The one below, a common green darner, shows the eyes of the dragon.
No, not the cyclops marking; the two white beans on either side.
Both types of odonate spend their first few years in water as nymphs (also known as naiads) and are about as bad-ass as an insect can get. Nothing is safe from them, including each other. And their jaws! Does everybody remember the movie Alien? The jaws within jaws thing? Yeah, dragonfly larvae can do that. Gah!
To be a bit less melodramatic,
Dragonfly nymphs capture their prey using their extendable labium, positioned underneath the head. At rest, the labium is folded away, but when prey approaches the nymph, the labium is thrust out faster than the prey can react, resulting in its capture. The labium is equipped with gripping jaws and sharp bristles which ensure that once captured, prey is retained securely in the grip of the nymph.
Even when they achieve maturity and take to the skies, they remain deadly predators, primarily due to their incredibly advanced vision. I found
two studies which showed dragonflies' high success rate (up to 95%) was due to it flying
where the prey was going to be.
We found that dragonflies fly directly toward the point of prey interception by steering to minimize the movement of the prey's image on the retina.
(from the second study)
My, what big eyes you have!
Another factor in their amazing hunting prowess is their ability to individually manipulate all four wings. This gives them the ability to move in six directions - up, down, forward, backward and side to side. I have to admit to being interested in the intricacies of dragonfly flight but it quickly goes over my head. Once scientists start talking about things like body oscillation and the Navier–Stokes flow equations, I'm lost. For those of a scientific bent and better knowledge, this article was deep enough to be interesting, while less knowledgeable folks like myself could still get the gist of it.
This short video shows a dragonfly in flight in slow-motion. Beautiful creature! (Sorry, I can't seem to embed the video.)
One last note of the unusual. Those incredible wings also show promise in nanochemistry. Apologies for the abbreviated article. The original is behind pay-walls at every site I visited. The gist of it is
Material inspired by dragonfly wings bursts bacteria
The scientists made a material based on studies of dragonfly wings which bacteria cannot adhere to and live. There are, of course, a billion or so uses for such stuff, from the medical industry to the food industry. Oddly, I can't find anything more recent than 2013 when it was first announced. Anyone out there have more current info?
Now, who's up for some pictures? I'm still learning how to ID them, no easy task, so any input would be welcome.
See how the wings act like a stained glass window?
Do you have any pictures of the dragonflies/damselflies from your area? Post them in the comments along with any dragon-related stories!
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