The Common Green Darner, Anax junius, is one of our largest dragonflies, measuring three inches long, with a four-inch wingspread. It is strikingly colored, with a green thorax and a bright blue (male) or reddish (female) abdomen. As if that weren’t enough to set this dragonfly apart, it is also migratory. Common Green Darners migrate south from August to November, stopping over (like migrating birds) occasionally along the way, resuming flight after resting and refueling. Thanks to radio telemetry, we now know that over a two-month migration, Common Green Darners, each weighing about one gram, can migrate over 400 miles. (Photograph is of a Common Green Darner perched on Bottle Gentian.)
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If you look very closely you will see that the adult Eastern Kingbird has just stuffed a female Widow Skimmer dragonfly (that it has caught and killed) down the throat of one of its nestlings whose beak is pointed skyward. Eventually, after much hard work, the young kingbird succeeded in swallowing the insect, wings and all. The parents will continue feeding their nestlings for at least three weeks after they have fledged.
Dragonflies (and bees) have the largest compound eyes of any insect, each containing up to 30,000 facets, or ommatidia (house flies have 6,000). Each facet points in a slightly different direction and creates its own image, and the dragonfly’s brain compiles these thousands of images into one picture. This eye structure enables dragonflies to be extremely sensitive to motion. Because a dragonfly’s eyes wrap around its head, it can see in all directions at the same time (though its forward-looking vision is the sharpest). When capturing prey, a dragonfly doesn’t chase it – it intercepts it in mid-air, and it’s successful nearly 95% of the time. This hunting technique entails calculating the distance of its prey, the direction it’s moving and the speed that it’s flying – an impressive feat any tennis, baseball or football player would especially appreciate!
(Photo is looking down on the eyes of a Common Green Darner. Three simple eyes, or ocelli, are located in the black section below (above in the photo) its two tan compound eyes. The short, thin black lines are its antennae, which can detect wind direction and speed. The yellow section is part of the upper half of its face, or frons.)
Meadowhawks are the only small red dragonflies seen in New England (most males are red, most females are brown).The latest species of dragonfly flying in the fall in this area is the Autumn Meadowhawk (Sympetrum vicinum), which doesn’t emerge until mid-summer. It seems a bit incongruous to observe these dragonflies not only flying, but mating and laying eggs in late October, but that is exactly when you can expect to see them. Until there have been several hard frosts, these winged masters of the air are able to keep active by basking in the sun and warming their flight muscles. The two pictured Autumn Meadowhawks are copulating in the typical “mating wheel” fashion, with the male grasping the female behind her head while the female places the tip of her abdomen at the spot on his abdomen (the seminal vesicle) where he stores his sperm. The female Autumn Meadowhawk lays her eggs in tandem with the male (his presence prevents other male meadowhawks from replacing his sperm with their own).
Twelve-spotted Skimmers are classified as “King Skimmers,” all members of which are large and conspicuous, often with distinctive wing patterns. Male Twelve-spotted Skimmers (pictured) have a grayish bloom on their abdomens and each wing has three dark spots with white spots in between them. Females have brown abdomens and no white spots on their wings. All summer you can see males flying back and forth short distances along the shores of ponds and over water, hovering as well as perching. They are territorial and patrol over water, loop-de-looping with competing males. A small number of Twelve-spotted Skimmers occasionally take part in Atlantic Coast migrations.
Beaverpond Baskettail dragonflies have an early flight season, first appearing in May in the Northeast. The males (pictured) cruise over the water (often beaver ponds, hence their name) as well as the shore in sexual patrol flight, flying back and forth over the same area repeatedly. After mating, the female accumulates a large egg cluster at the tip of her abdomen, and as she drags it along the surface of the water, a long string of eggs is draped over plants. Once these strings expand, they can be several feet in length and an inch or more in diameter.
Often on hot, sunny days you will see dragonflies perched facing away from the sun, with their abdomens raised high in the air above them. This position actually has a name – the obelisk posture – and some dragonflies and damselflies assume this position to prevent overheating. They raise their abdomen until its tip points at the sun, minimizing the surface area exposed to it. The name given this posture comes from the fact that when the sun is directly overhead, the vertical alignment of the insect’s body suggests an obelisk. The meadowhawk dragonfly in the photograph assumed the obelisk posture several seconds after the sun came out from behind the clouds. As soon as the sun was obscured by clouds again, the dragonfly would lower its abdomen to a horizontal position. It continued doing this for a considerable amount of time. Sometimes abdomens are raised for reasons other than temperature control, including threat displays during conflicts.
Dragonflies (and damselflies) form what is called a “mating wheel” when they mate. The male (top) grasps the female at the back of her head with the appendages at the tip of his abdomen. The female then curls her abdomen forward so that its tip reaches his sex organs and receives his sperm. After mating, the male may continue to grasp the female and accompany her while she lays her eggs, to prevent another male from removing his sperm from the female and then mating with her.