Greetings, BugFans,
2016 – The BugLady is still out looking at/for bugs, so this is a combination of several bygone episodes about our spring dragonflies. The 2016 dragonfly season is starting slowly – some migratory darners appeared a few weeks ago but then disappeared when colder weather came back. In the past week, the BugLady has seen a Common whitetail, a Chalk-fronted corporal, and some Whitefaces, plus a handful of damselflies. If you check the archives at the UWM Field Station link below, you’ll find that dragonflies have not been neglected.
A genuine, sometimes tentative, sign of spring is the reappearance of dragonflies, but the first sightings may not be of local individuals. COMMON GREEN DARNERS (family Aeshnidae) (whose scientific name, Anax junius, means “Lord of June”) migrate south in fall and repopulate the North Country with each spring. They return, often when the snow still lies in sheltered spots, as the insects they prey on take to the air.
The Green Darners that deliver the spring lay eggs that hatch into (aquatic) naiads that take the whole summer to mature. These offspring make the trip south in fall (fall dragonfly flights along the Lake Michigan shoreline can be inspirational), and the generation after that will return to Wisconsin. There is increasing speculation that in addition to its spring migrants, Wisconsin has non-migratory, resident Common green darners that emerge at about the time that the migrants have finished breeding and are completing their life cycles and replaces them in our skies, and their naiads overwinter in frigid water under the ice.
Darners are big insects, with bodies exceeding three inches and wingspans of four-plus inches. Both sexes have a green thorax, but the male’s abdomen is blue and the female’s is brownish. They have wrap-around compound eyes (each containing up to 50,000 simple eyes) and a characteristic “Cyclops-like” “bulls-eye-like” spot in front of their eyes. Whether migrant or native, darners are a challenge to photograph – they “never land,” and they use all those eyes to spot photographers.
The warming of the water in spring is a powerful and irrevocable trigger. Water changes temperature slowly – a lot of energy is needed to move it just a few degrees in either direction. The next dragonflies on the scene signal that the water has warmed. Their naiads crawl out of the water and out of their nymphal skins, pump up their wings and become creatures of the air, chasing their prey – flashes of wings that the dragonflies spot from perches or while hovering.
COMMON BASKETTAILS (Epitheca cynosura) are drab dragonflies in the Emerald Family (Corduliidae). They sport a black spot at the base of each hind wing, muted orange bars on a black abdomen, and short, gray hairs on their thorax. As Cynthia Berger explains in her book Dragonflies, “like real fur, the fuzz helps hold in the heat generated by those muscle contractions [contractions of the flight muscles, which raise the temperature within the thorax]. Like darners, they perch vertically rather than horizontally, often hanging down from a twig tip. Baskettails are agile flyers that may be seen in the afternoon hunting in groups above swarms of smaller insects like midges.
The “baskettail” in Common baskettail refers to the “basket” of eggs a female will carry under her abdomen and ultimately attach to underwater plants. According to bugguide.net, the genus name Epitheca is derived from epi (above) andtheca (pouch or basket); a female carts her eggs around, sometimes all day, abdomen elevated, looking for the right spot to deposit them. Once she finds it, she may attach her ball of eggs to a submerged plant and then depart, or she may drag/tap her abdomen along the water’s surface, unraveling her string of eggs as she goes. In either case, the once-compact egg mass swells into a strand an inch wide and six inches to several feet long.
The BugLady founds scores of baskettail exuviae (skins shed by the naiads when they emerge as adults) at a wetland the other day but saw nary an adult.
CHALK-FRONTED CORPORALS (Ladonia julia), in the Skimmer family Libellulidae, are northern dragonflies that often emerge in early May. Adult males have white “corporal’s stripes” on the first segment of their thorax and white on the first few abdominal segments. It’s called pruinosity, and it’s caused by an opaque, generally white/blue-white, waxy substance that develops on the cuticle that covers the dragonfly’s exoskeleton (usually the abdomen, but sometimes other body parts) and gives it a powdered or hoary appearance. Pruinosity is not only a sign of aging, it’s an indicator of breeding readiness). Female Corporals are rusty brown with traces of white markings at the thorax and abdomen, and juveniles are a pinkish-brown with thin “shoulder” stripes and a black line down the center of the abdomen.
Adult Corporals grab flying insects from royal ant/mosquito-size through small dragonfly-size. They often perch on, bask on, and even hunt from the ground or a rock, and on cool days, hundreds may congregate on warm road surfaces. They are known to follow people and pick off circling mosquitoes and deer flies. Much has been written in these pages about the benefits of aposematic (warning) coloration and about the up-side of mimicking an aposematically-colored insect, and the Corporal appears to have read none of it. In studies of food preferences, Chalk-fronted Corporals chose their prey by size – small prey over large, but they didn’t seem to care if it was wasp-colored or not.
Darners and Baskettails and Corporals – Oh My!
And then there are Whitefaces.
It would be hard to conjure up a more logical name for the DOT-TAILED WHITEFACE (Leucorrhinia intacta, family Libellulidae) than Dot-tailed whiteface. Both males and females have the “dot-tail” and the “white face,” though females tend to have a few yellow splotches along the top of the abdomen, and juveniles have, temporarily, even more. All have a black triangle at the base of the hind wing, and like some of the other early dragonflies, whitefaces have a pretty hairy thorax.
There are seven species of whitefaces in north of the Rio Grande, some with spectacular bands of crimson on their abdomen and thorax. The Dot-tailed whiteface cuts quite a swath across the continent, though its range is largely in the northern states and Canada.
Dot-tailed whitefaces enjoy most kinds of quiet waters – bogs, marshes, swamps, sloughs, farm ponds, and even very slow streams – as long as there are low aquatic plants to perch on. They bask on floating water lily leaves and on the ground, and they don’t gain much altitude when they fly. The BugLady frequently sees them in her grassy field, some distance from water. They emerge by late spring and fly through a good chunk of the summer into early fall.
The BugLady