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Sep 08, 2024
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The congregations or ‘swarms’ of Blue Darner dragonflies being observed over the past couple of weeks in various regions of the province are the result of having an ample supply of food — smaller flying insects.
This is according to Dr. James Tansey, provincial entomologist with the Saskatchewan Ministry of Agriculture.
Dragonflies, and their smaller close relatives damselflies, consume smaller flying insects that can bug anyone trying to enjoy the great outdoors, such as biting midges (also known as no-see-ums), and even mosquitoes.
“Saskatchewan has a pretty good diversity of habitats, and with that diversity of habitats, you’re going to get a diversity of insects, and that’s dragonflies and their allies or their close relatives to the damselflies.
“Both those groups belong to the same order. They’re divided into different suborders, in large part due to their wing musculature and the way they hold their wings. So there are conspicuous differences between the two, but they’re all predators.”
The Blue Darners, members of the Aeshnidae family, are “conspicuously long-lived” creatures, according to Tansey.
“The adults are predacious. The nymphs are predacious, and they’re pretty voracious predators as nymphs,” he shared.
“They can live in bodies of water for multiple years. So they complete their development under there, go through a series of molts, get larger and larger, and when they’re large enough to complete their development, so that is to climb out of the water and do that final molt into adulthood they’re big enough where they’re taking down small minnows and tadpoles, and they’re quite voracious predators.”
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‘Alien’ movie monster based on dragonfly
In fact, Tansey said the Xenomorph monster in Ridley Scott’s “Alien” movie franchise, which “has a set of jaws that come flying out of its mouth”, was inspired by the mouth of the dragonfly nymph.
He said any dragonfly with wings is an adult. It won’t go through any more molts, won’t get any bigger, and will pass away in winter — unless it is one of the species that prefers to migrate south.
“Certainly there are a large number of them. I think the congregations of them that you’re seeing is probably more a reflectance of prey availability. So you’re going to see them in areas where you’ve got a lot of midges flying, or prey items that they can take down.”
Large dragonflies, much like their juvenile counterparts, are voracious predators, and will even consume other large dragonflies, but only because they go after anything that’s flying.
“If they come across it, they’ll give it a whirl and they’ll try to eat it.”
Tansey himself has been bitten by a dragonfly’s large, powerful mandible when the creature flew up his sleeve while he was motorcycling, and, “he let it be known that he wasn’t very happy to be there. So I got a couple of nips.”
“As a rule, they’re picking on other smaller flying insects, and they have a really neat trick to do this. They’ll simply fly forward and have their legs cupped in a basket, so it’s a little bit like filter feeding,” explained Tansey.
“They’re literally flying through the environment and they’re filtering other flying insects, particularly small ones, out of the air into this leg-basket, and then just haul them up to their mouths and munch away.”
He said if there is a concentration of prey items in a region, this will attract the predators. And dragonflies don’t just excel at catching prey due to their leg-baskets, they also have large compound eyes with 360-degree vision.
“They have no blind spots. How they process this is a mystery to me. I’m hoping somebody figured that out,” he said.
“The actual processing of all that visual information would certainly be a challenge for any brain, but they seem to do it and they’ve done it for a very, very long time.”
Dragonflies are most active at dusk, but they can also be seen hunting during the day, and, since they are so good at flying, and have such acute vision, they’re not easy to discourage.
While most people would not want to discourage dragonflies, given they most often consume bothersome insects, attracting dragonflies would require encouraging their prey items.
An ‘interesting mating strategy’
Tansey said soon the dragonflies will be flying in tandem, as mating season begins.
“They have a bit of an interesting mating strategy,” he shared. “Boy will meet girl, and then the male has, on the end of his abdomen, what’s called a clasper, and he is going to literally grab her around the neck with this clasper, reach inside the female with what’s called a sperm scoop, and he’s going to empty her of contents, and then meet with her and then hang on for dear life. So it’s a little like rodeo romance.”
Once the male’s sperm can get incorporated into that female’s spermatheca, an organ that a lot of insects have, it is really for sperm storage.
“They can hang on to that for some time and keep sperm alive, and use that sperm as the eggs mature,” he explained.
“So once that occurs and he’s convinced that he is in fact the father — no visit to a daytime talk show required — then she will go and lay eggs and deposit them on vegetation very near the water just above the water surface. Those will hatch up, fall into the body of water, and the nymphs will begin their development.”
Tansey encourages people to take their kids out and do some dip netting in sloughs, to see what kinds of diversity can be found in Saskatchewan’s freshwater systems.
This means scooping up and examining things like dragonfly nymphs and other species, but returning the animals back to the water, without harming them in the process.
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