Flight. My summer has been dominated by consideration of the beauty and challenges of flight. In typical fashion, in this post I have awkwardly juxtaposed two interests of mine. So, at its end, this post dashes from dragonflies to biplanes. Be warned.
Inspired by the exquisite photographs of dragonflies taken by a friend, I’ve spent far too much time this summer in pursuit of these insects with little to show for the effort. Dragonflies are members of the Odonata order, along with damselflies, and specifically of the infraorder Anisoptera. (Infraorder, a new term for me, is a taxonomic grouping below a suborder and above a superfamily. I assume this is a generally accepted taxonomic grouping term.) Dragonflies are quite ancient; the Protodonata appear in the Late Carboniferous, some 325 million years ago. Sporting a monstrously large wingspan that could reach some 30 inches, the Protodonata had key similarities (though not size) to today’s dragonflies, but they went extinct during the Triassic. True Odonata insects appeared during the Permian, over 250 million years ago, and have remained largely unchanged since. (Much of this discussion is based on Introduction to the Odonata, provided by the University of California Museum of Paleontology.)
The image below shows a dragonfly fossil (Tarsophlebia eximia) from the Late Jurassic (between 150 and 145 million years ago) which was found in Germany’s Solnhofen limestone.
(Wikimedia Commons reports this image to be in the public domain.)
It is impossible I think to spend any time watching dragonflies and not consider what it means to fly. These implacably hungry carnivorous insects are on a continuous hunt as they cut through the air in abrupt slashes, darting with purpose. Their sharp aerial dances (remarkably lethal for their prey) are punctuated with moments of hovering. Then all this ceases for often long periods of motionless rest on, say, a plant leaf or stem (or, even, a clothesline or the back of a mottled plastic lawn chair). During these pauses, their four wings remain spread, open to the sun and to inspection. These are the opportunities to try and capture the image of this ancient creature.
Two of my more successful pictures of dragonflies appear below. The first shows a female dragonfly on a clothesline and the second a male on a plastic lawn chair. Both specimens are of the species Pachydiplax longipennis, commonly called Blue Dasher. These individuals are roughly 1.5 inches long from head to tail and exhibit sexual dimorphism in their color differences.
Dragonflies’ heads are mostly eyes (clearly, this is a predator) which can provide a wonderful canvas for coloring. The distinctive wings are attached to the second and third sections of the thorax. The long, needle-like abdomen offers another place for distinctive colors.
As entomologist Scott Richard Shaw, in his fascinating book Planet of the Bugs: Evolution and the Rise of Insects (2014) (reviewed previously in this blog), observes, the extended-wing posture of dragonflies at rest is a telltale sign that these are paleopteran insects. That is, dragonflies along with mayflies, are so-called “old-winged” insects. As he writes:
The most ancient wing style – a flat panel of skeletal material set into a membranous area at the top of the thorax – was very simple but highly efficient, and some modern insects such as mayflies and dragonflies still sport it. (p. 81)The old-wing configuration, a breathtaking innovation when it first appeared, involves the snapping of the animal’s wings. The wing upstroke is generated by muscles internal to the thorax (not attached to the wings) which change its shape causing the upward movement of the wings. The wing downstroke is propelled by muscles directly connected to the wings. It’s these flight muscles that allow for some tilting of the wings necessary for navigation.
Most obviously, the old-wing construction prevents these insects from doing what the myriad neoptera (new-winged) insects of today take for granted: they can “twist their wings at the base, fold them back over their body, and put them away” (p 88), making them smaller targets for predators. (I'm puzzled, though, by the photograph I took of the female shown above. What were her wings doing and how did they do that? After posing for the picture, she flew off without a hitch.)
Shaw devotes a chapter to an exploration of insect flight. He notes there are some fundamental questions which remain open to debate, but he is not shy about positing the answers he believes make the most sense. Though he considers how wings evolved, what interests me more is what he has to say about why they came into being.
For millions of years in ancient time, insects were the fliers, the animals having airspace to themselves. Flight appears at a time in the Carboniferous (say 320 million years ago) when trees become abundant. Rather than believe that the early insects climbed tall plants in search of edible parts of the plants and then came to launch themselves into the air, relying on body parts conducive to gliding, Shaw asks, Why would they make that climb in the first place since seeds and spores would eventually fall to the ground? He argues that insects would have been prompted to climb in order to reach sunlight, they are, after all, cold blooded. Protowings would then serve as “solar panels” –
[t]he larger structural veins of the wings are hollow, so blood blows into them, allowing heat to transfer back into the body. Even small protowings would have had the potential to transfer valuable heat, possibly before the panels could be used for flight. (p. 78)That, in his estimation, is a more persuasive reason for climbing plants in the first place. But, at some juncture, he postulates it became easier to descend the plants by pushing off into the air relying on protowings for a safe descent. Further development of wings would have been prompted by, among other reasons, courtship and mating (wings can feature colors and patterns), camouflage (colors and patterns), escape from predators, and dispersal of the taxon.
A wrenching pivot happens right here.
It’s only been appropriate in this year of 2019 to be thinking about flight, but not necessarily of the insect kind, rather, of the human kind.
I’ll try to make this change of course less jarring by referencing writer Jay Spenser who, in The Air Plane: How Ideas Gave Us Wings (2008), suggests that the construction of heavier-then-air craft may owe a debt of gratitude to the insect world, and specifically the dragonfly. Frankly, I think Spenser is reaching for it, but, oh, why not? The example Spenser provides is that of the monocoque (one-shell) construction that, in the early 1900s, helped make some airplanes lighter and sleeker. In essence, under this approach, the exterior shell (read exoskeleton, like that of an insect) of the fuselage bears the stresses of flying, eliminating the need for internal supports. This mode of construction works only for smaller planes, while semi-monocoque construction, where the load bearing is shared by the outer shell and some internal supports, remains in use for today’s large airliners. Spenser writes,
. . . it’s the dragonfly with its long body and prominent wings that serves as nature’s poster child for monocoque construction. (ebook version, p. 70)Now that I’ve obfuscated the transition, I’ll turn to flight by humans. Yes, this year’s the 50th anniversary of the Apollo 11 flight and the first walk on the Moon. I thoroughly enjoyed the documentary film Apollo 11 now streaming on Hulu which offers incredible contemporary footage of the trip. (Complete with the jarring appearance of Vice President Spiro Agnew at the launch and the stilted words of congratulations later from his boss.) But, for me, all the hoopla this year about Apollo 11 is only a relatively small part of what makes this year important in terms of flight.
There’s a signal aviation event that needs to be celebrated this year: the first non-stop flight across the Atlantic a century ago in 1919. And, no, that’s not Charles Lindbergh’s thing (which was the first solo flight across the Atlantic on May 21-22, 1927). Rather, what should be memorialized this year is the flight on June 14-15, 1919, by British aviators John Alcock and Arthur Whitten Brown in their Vickers Vimy biplane. They covered the 1,880 miles across the Atlantic from Newfoundland to Ireland in somewhat more than 16 straight hours. Brendan Lynch has written an authoritative account of that journey in Yesterday We Were in America: Alcock and Brown, First to Fly The Atlantic Non-Stop (2019). Well worth reading. The Vickers Vimy with Alcock at the controls and Brown navigating is seen below as it left St. John’s, Newfoundland, on June 14.
(Wikimedia Commons reports this image to be in the public domain.)
The two were international celebrities after they landed in Ireland, though, sadly, Alcock was to enjoy that status only briefly, dying in a plane crash in December of that year.
Admittedly, the Vickers Vimy was no sleek beauty, no obviously aerodynamic masterpiece, no poetry in motion. Yet just as the dragonfly’s old-school wing construction was (and remains) effective, so, too, did the bi-winged/box-kite structure of this plane enable it to take a giant leap in our aerial adventure.
Posts
