During all stages of their lives, dragonflies are fearsome and efficient hunters. If dragonfly larvae were eight to sixteen inches long, as they probably were 300 million years ago, we would dare not swim in fresh water for fear of being attacked. Any moving, living thing could be prey for dragonfly larvae, including other dragonfly larvae, daphnia, mosquito larvae, tadpoles and even small fish. (Several of my daughter’s goldfish fell prey to my good intentions when I brought home a large Common Green Darner larva. At the time, she didn’t appreciate the scientific aspects of the experience at all.) Aquatic larvae are very visual; any nearby movement is noticed. Their antennae are very sensitive and are used as tactile sensors, picking up even slight movement. Prey is secured primarily through the use of the powerful, extendable lower lip (labium) that is equipped with “teeth.” In as little as 1/100 of a second, the labium can be extended out to 1/3 the length of its body, snagging the victim with the teeth and delivering it to the waiting jaws underneath
Some dragonfly larvae, such as the darners, stalk their prey among the plants and detritus of their underwater jungle. These “crawlers” are able to see a moving target from a distance of several inches and will slowly pursue prey in a cat-like manner until within striking distance. Other larvae, such as the emeralds, skimmers and the long-legged cruisers, are “sprawlers,” blending into the bottom materials with camouflaging markings or by a build up of silt on body hairs. Sprawlers lay in wait with their antennae laid out on the muck or sand until suitable prey happens by. A third hunting style is demonstrated by the “burrowers.” Most clubtails (with the exception of the Dragonhunter, a massive sprawler) and spiketails are burrowers who disappear below the sand or silt, only their eyes and the tips of their abdomens are visible. They lunge at anything that comes within striking distance.
Despite their skill as predators, the larvae are also heavily preyed upon by fish, birds, predatory aquatic insects and other dragonfly nymphs. Larval gills are located inside their abdomen and water must be pulled in through the rectum and expelled for them to breathe. To avoid predators they accelerate this process and effectively become “jet propelled.”
Adults are also fearsome predators that have even been known to take down a hummingbird. Their hunting prowess is due in no small part to large eyes, resilient and maneuverable wings, spiky legs that form a snagging net and a powerful, muscular thorax serving both the wings and the legs. Adult dragonflies capture exclusively live prey and almost always while they are on the wing. Flying insects are located visually and smaller prey is caught directly by the mouth. Larger insects are snared in a basket that the dragonfly forms with its legs, transferring the food to its mouth after it has been secured. Prey is either eaten on the wing or from a perch. The hard parts of beetles and wings of butterflies, moths, damselflies and other larger insects are discarded and may be found below a favored perch by the observant naturalist. If you can approach close enough to a chewing dragonfly you will be able to hear them “crunch, crunch” on the exoskeleton of their “McBug” sandwich. Back to the top
Because warmth is needed for activity and an efficient metabolism, most dragonflies disappear to protected perches on cool days or when the sun disappears behind a cloud. Despite the fact that insects are “cold blooded,” many dragonflies maintain an internal temperature as high as 110 degrees F. This is accomplished by the burning of calories during physical exertion and by staying in the sun. A cold dragonfly preparing to get the day started will shiver its wings to create heat in its thorax until it has warmed itself enough to take flight. Some dragonflies, such as the Ebony Boghaunter, Stygian Shadowdragon and the blue darners have adapted to cooler weather as a method of allowing early- or late-season emergence or to take advantage of the plethora of insect life that becomes active at dusk. Some species will be seen flying well after sunset on moonlit evenings or under street lights.
In hot, sunny weather it is important that dragonflies don’t overheat. Cooling strategies include becoming less active, moving into shade and changing their body position. The obelisk position orients the dragonfly’s abdomen directly at the sun, thereby reducing the surface area exposed to solar heating. Some dragonflies also point their wings forward and down in order to reduce exposure to sunlight and, perhaps, to reflect light and heat away from their bodies.
Dragonflies drink by thrusting their bodies down onto the water’s surface in a sequence of one to three splashdowns. Water is absorbed through the exoskeleton. Dew is also absorbed on cool mornings. Back to the top
Certain species of dragonfly migrate, either en masse or individually. Dragonflies follow weather fronts, fleeing cold fronts in the fall on their way south and chasing warm fronts in the spring when moving north.
The best-known migrant is the Common Green Darner, who makes a one-way trip south in the fall and whose offspring makes the return one-way trip north the following spring. Another seasonal migrator is the Variegated Meadowhawk who may be seen in early spring returning from year-round haunts in Oklahoma, New Mexico or Texas. It is risky business though, as April snow and cold can strand and freeze thousands.
Frank Nicoletti, the head hawk-counter at Hawk Ridge in Duluth, has observed that the peak American Kestrel migration every fall coincides with the peak Common Green Darner migration down the North Shore of Lake Superior. He believes the kestrels rely on the large dragonflies as a food source during the trip south. While the kestrels tend to ignore the green darners at midday, concentrating rather on making miles, later in the afternoon they start feeding heavily on them.
Sometimes in the fall, flocks of migrating Common Nighthawks have been observed flying above swarms of Common Green Darners, both creatures feeding on masses of smaller flying insects. The nighthawks typically do not prey on the dragonfly. Both species tend to keep to their own space. The relationship appears to exist only due to the concentration of small insect prey. Back to the top
Unlike butterflies, there are no dragonflies that overwinter as adults in the North Woods. Most winter beneath the ice in the larval form in a state of diapause, which is a sort of suspended animation. Other species, such as some of the meadowhawks, lay their eggs along shorelines where the eggs will sit through the winter until high water in spring washes them into the lake. Back to the top
The above text from: Dragonflies of the North Woods, by Kurt Mead, with permission of Kollath Stensaas Publishing.