Sex and Identity Among Red Dragonflies
Sex and Identity Among Red Dragonflies
A Summertime Drama of Survival and Deception
NO MATTER how uncertain our lives, how troubled our politics, even how dire or existential the threats to humanity, at least one thing is reliable and wonderful across much of the world right now: the red dragonflies of summer.
Named “meadowhawks” or “darters,” depending on where you live, they dash and hunt and pose in meadows, at ponds and wetlands, even beside watery roadside ditches. All of which would be routine and audacious enough for dragonflies — and for us. But there’s even more to meadowhawks and darters: a drama of subterfuge and sexual identity worthy of Shakespeare. And it’s almost certainly being acted out on stage near you.
Jaunty and approachable, meadowhawks (as they’re called in the Americas) and darters (in Europe, Asia, and Africa) — about 56 species worldwide in the genus Sympetrum — are fairly easy to find. Search near water (not rivers) for dragonflies about 1.5 inches (nearly 4cm) or so in length and often perched waist-high in plain sight at or near the tips of vegetation. Although various meadowhawk and darter species differ only slightly in appearance, mostly by their black accent markings, females are customarily yellow and males ruby-red.
Except when they’re not.
Sometimes males are yellow and females are red. And in this cross-dressing, if you will, even the casual dragonfly watcher can witness the struggle for existence and a ruthless game of reproduction. So before you yourself go searching for the red and the yellow dragonflies and their dramas, here’s your lesson in color, sex, and deception.
Sexual Dimorphism
Sexual dimorphism simply means that males and females of a particular species appear different from one another. Birdwatchers know it well. For example, like our dragonflies Scarlet Tanager males are red and females are yellow-green. Sexual selection generally drives these differences. Males get color and other ornamentation to flash at females during courtship displays. Females are cryptic so that they might better elude predators. Bearing and raising young, after all, can be perilous enough for a female.
Meadowhawks (as I’ll call them and the darters henceforth) are classically sexually dimorphic: males red, females yellow. But here’s a twist: male meadowhawks (and male tanagers, for that matter) begin life on the wing yellowish in color, looking very much like a female for some period before turning red. (Those are both male meadowhawks in the image atop this post.) This delayed onset of color actually isn’t so unusual either. Being cryptic for even a few days or so offers a young male dragonfly benefits in the struggle for existence, at least two of which are fairly standard:
Reduced risk of predation. Freshly emerged dragonflies, soft and squishy and awkward in flight (we call them tenerals), are easy prey for birds (even other dragonflies). When you’re young and weak and male, it helps to hide out for a while and not be bright red — at least not yet.
A feminine facade. Mature, red male meadowhawks can be brutish toward other red males in the battle for turf and access to mates. The bullies are presumably less likely to harass young yellow males resembling females. It’s a kind of female mimicry against aggression — and it’ll return to it soon.
During the early yellow phase in his life, a male meadowhawk isn’t growing any larger, but rather girding for the arena of reproduction. His tissue hardens. He becomes more agile in flight. His reproductive organs mature. And ultimately he turns from yellow to red. A similar transformation happens among females but without the change in coloration.
Among males, red means go: sexual maturity. It’s presumably a signal to a female that, yeah, this male is a survivor, now fit and worthy enough to supply half the genes for her offspring. It’s standard sexual selection theory among lots of wildlife (and dogma among wildlife biologists). It would seem logical for the red dragonflies. But among the many things I admire about dragonflies is that they defy logic and dogma.
One problem with the red-and-ready hypothesis is that I’ve seen (rarely) female meadowhawks mating with yellow males — the youngsters. What’s with that? Well, for one thing, with certain species as notable exceptions, male dragonflies don’t exactly prance around and flash their stuff in order to attract females as mates. Dragonflies aren’t like birds-of-paradise, with males performing courtship displays and females selecting the most elaborate or impressive as a proxy for fitness and good genes. As it turns out, how red the meadowhawk probably doesn’t matter much (if at all) to a female.
That’s not to say red doesn’t matter in the mating game. Red matters a lot in nature. Another form of sexual selection is more likely in play among male meadowhawks: intrasexual selection, male versus male, classic examples of which include rams butting heads or birds singing to claim territory in the competition for access to females. Unlike many other dragonfly species, male meadowhawks compete for perches. A given male takes one and holds it like king of his hill. (It’s a shared behavior among dragonflies in the same family as meadowhawks: Libellulidae.) We can debate the extent to which these constitute classic territories defended by the red males. But perch preference is something you’ll almost certainly see when you find meadowhawks for yourself. Flush a male from his perch, and he’ll likely return to it soon enough.
There’s not a lot of research on this among meadowhawks, but males hold a perch for at least two reasons: it’s a good vantage from which to spot and hunt prey (smaller insects flying by), and it’s good for spotting potential mates, especially close to water’s edge where females tend to hang out. More speculative would be that it’s also good for attracting females, which assumes that she would be more receptive to mating with a male holding a prime perch (and which in all likelihood is not the case).
Make Love Not Then War
As promised, let’s return to our young yellow males — and perhaps a kind of triumph over aggression. Another angle on the delayed onset of color in meadowhawks is that a yellow male resembles a female. And that might actually afford him greater access to females for mating.
As those blaze-red males are holding their perches or vying for access to mates, the young yellow male can avoid the fracas and instead linger among females. This “subordinate male,” as biologists call him, might therefore more easily get himself a copulation. (That crafty guy, er gal, er guy.) This subterfuge, sometimes called “sneak copulation,” isn’t that unusual in nature, having been observed among certain kangaroos, lizards, fish, and primates (with no comment on my part among human primates). To be clear, I’m not entirely sure it’s been proven among meadowhawks and darters — but I would not be surprised if those yellow males sneak a copulation before turning red and then heading off to battle other males.
In any event, yeah, of course the world’s competitive, brutal, uncertain, and beautiful. And regardless of whether the meek shall inherit the Earth, at the very least the yellow male meadowhawks and darters remind me of a way to be on Earth with neither aggression nor warfare as the only options — not even a lofty perch.
Postscripts
Male dragonflies aren’t alone in color coding. Females, as they age, can change color to resemble males. It doesn’t happen often, but often enough, particularly among some of the small pond damselflies: bluets in the genus Enallagma, for example, and forktails in the genus Ischnura. So why would a female dragonfly resemble a male? For one thing, other males might be less inclined to check her out — even seize her — as a possible mate. Routine harassment like that by males can hinder a female’s ability to hunt prey for herself and generally get on in the world, including laying her eggs in peace after a previous mating.
Many of the meadowhawk and darter species (genus Sympetrum) are difficult to distinguish from one another, even with a good photograph — they must instead be identified in the hand. Two common exceptions (picture just above) are Variegated Meadowhawk (Sympetrum corruptum), which is distinctive and widespread in the central and western U.S., and Autumn Meadowhawk (Sympetrum vicinum), flying across the eastern U.S. and to a lesser extent the Pacific Northwest, and somewhat unusual for having yellow legs instead of black. The most abundant darter in Europe is the handsome Common Darter (Sympetrum striolatum).
Dennis Paulson and Josh Lincoln reviewed and improved an early draft of this dispatch.
Something you didn't mention is that dragonflies mate by indirect sperm transfer. That's what the tandem flight is about. I recall a paper years ago that showed that males sometimes grab other males in tandem, remove that male's sperm from the pocket on the second abdominal segment, and replace it with their own. A female mating with the pirated males thus gets the "counterfeit" sperm from the initial male. In reference to your comment that dragonflies also prey on each other, here is a link that shows exactly that: https://www.youtube.com/watch?v=RawnujgPqF8. I don't know what species these are, but maybe you do.
Great article, thanks! I really enjoyed studying sexual selection as a theory early in my career. The dragonflies remind me of learning about the ‘sneak’ strategy used by some fish (from what I recall) in which sexually mature males maintain a juvenile phenotype to get access to females instead of battling the big boys. What’s super interesting is how some of the morphology obviously responds to the heightened hormone exposure (e.g., reproductive organs) but other parts of the body don’t (e.g., cells producing pigment) in these individuals. Nature is so cool 😎