Field Guide To Migratory Dragonflies
This guide is intended as an aid to identify migrating dragonflies.
Dragonflies are not difficult to identify when perched at close range or in the hand, but it becomes more difficult when they are moving rapidly in flight, which of course is what migratory dragonflies are likely to be doing. Nevertheless, all of them perch at some time, so it is possible with persistence to get a good look at and identify dragonflies that may be passing through your area.
A basic knowledge of dragonfly anatomy is of value. Dragonflies have a head, thorax and abdomen.
The wings are attached to the top of the thorax and the legs to the bottom, so it can be seen that the thorax is tilted backwards. Thus the part between the head and the wing bases is the front. An insect thorax has three parts, each with a pair of legs. The prothorax in dragonflies is a small necklike section separated from the other two sections, which are fused into a synthorax; they bear the middle and hind legs and the two pairs of wings, and much of their bulk is taken up by the big flight muscles.
The abdomen is made up of 10 segments, numbered from front to rear. Segment 1 (S1) is very small. The sexes can be distinguished by the shape of the abdomen. In males the reproductive apparatus is visible as a distinct bulge, with structures called hamules projecting below S2 and plainly visible from the side. They are more visible in some species than others, but a close look should distinguish them. Females lack the projecting structures and instead have a generally wider abdomen, enlarged to carry lots of eggs. The appendages at the tip include two pointed cerci in both sexes, and a broad epiproct in males, below the cerci and shorter than them.
FLIERS VS. PERCHERS
Dragonflies are of two types when it comes to foraging behavior. Fliers fly around to capture insect prey or look for other dragonflies, and perchers rest on perches much like flycatching birds do, keeping watch for potential prey, predators, or members of their own species. Some of the migrant species are fliers, others are perchers, and this will be indicated. Perchers orient more or less horizontally when perched, and they often turn their heads, actively aware of the environment. Fliers do not look around while perched and tend to hang at a diagonal or even vertically below their perching substrate.
Note that all dragonflies in migration will be doing about the same thing, flying on a steady course in one direction. At this time, perchers and fliers will be behaving similarly, and some of the many field marks described below will not be visible. Capture or photography of flying individuals might then be essential for positive identification, but migratory dragonflies also may land during migration, especially when tired or when ready to roost.
There are five confirmed widespread migrants, four of the flier type: one darner, two gliders, and a saddlebags. The other well-known migrant, the meadowhawk, is a percher. These species are emphasized in this guide. After the primary species, an additional 11 species that have been considered migratory at some places and times in North America are described.
OTHER MIGRATORY SPECIES
These species have been found in assemblages of dragonflies, mostly along the North Atlantic coast in fall, that were thought to be in migration.
Swamp Darner (Epiaeschna heros)
This very large darner, longer than the Common Green, has a brown thorax with prominent green stripes and a dark brown to black abdomen, ringed with fine green lines. Only the Regal Darner, with more green than brown on the thorax, could be mistaken for it. Both species may be in feeding swarms, but only the Swamp Darner has been observed in directed migration in northeastern United States.
Taper-tailed Darner (Gomphaeschna antilope)
This is a very small darner of the Southeast, with scattered records north to Michigan and New York. It is overall dark and rather dull-colored, with irregular and rather obscure paler stripes on the thorax and paired spots on the abdomen, some of them dull orange. Although very poorly known in general, individuals have regularly been found in southbound migratory movements along the Northeast coast.
Carolina Saddlebags (Tramea carolina)
This species is very much like the Red Saddlebags, but males have a dark purple face and darker eyes. Females are even more similar to female Red, but have a touch of purple on the face. Both sexes have S8-9 mostly black, while in Red, there are black spots on top of the same segments. Both body size and wing patches are slightly larger than in Red, not very apparent in the field.
This southeastern U.S. species is thought to be partially migratory, individuals showing up in spring in northern states, well to the north of where it is common. Small numbers of them are seen in Atlantic coast migratory movements in fall. All saddlebags are similar in habits to the Black Saddlebags and may be similarly migratory, although if so, it has been much less obvious.
Red Saddlebags (Tramea onusta)
Red Saddlebags are like Black Saddlebags, but the entire body is red (tan in immatures). S8-9 have black spots on top. The broad hindwing patches (“saddles”) are red to almost purple.
Another tropical and southern species, it is common in the Great Plains, east to the Mississippi and Ohio rivers, and ranges widely in the Southwest but is uncommon, perhaps only a sporadic migrant, east of the Appalachians; apparently resident in peninsular Florida.
Striped Saddlebags (Tramea calverti)
Four species of saddlebags have “narrow” saddles. Only the extreme base of each hindwing is darkened. This is a red species, the thorax with two pale diagonal stripes on either side, conspicuous in immatures and females but obscured in males. The abdomen has a black tip, with segments 8-9 almost entirely black. Females have a brown thorax and reddish-tan abdomen.
The Striped is the most northerly ranging of the narrow-saddle saddlebags, with vagrant individuals moving north in summer almost to the Canadian border. Large movements have been seen at several tropical localities, probably not latitudinal migrations.
Band-winged Dragonlet (Erythrodiplax umbrata)
Males are quite distinct, a medium-sized skimmer with black body and prominent wide black band across each wing at midlength. Females and young males are yellowish to tan to khaki color, the thorax brown in front with a vivid white midline. There are black or dark brown markings down the center and low on each side of the abdomen, becoming larger to the rear and finally almost covering S8-9. Terminal appendages in both sexes are whitish. A minority of mature females look like males, with black bodies and wing bands, but most just get darker and duller as they age. The wing bands are visible as brown washes in young males and darken slowly with age.
This species is abundant in the tropics and north into southern United States. It has bred as far north as Ohio rarely. A huge aggregation estimated at millions of individuals was once observed in July on the Texas coast, in migration or dispersing from a very successful breeding population.
Blue Dasher (Pachydiplax longipennis)
Immatures and females of this small skimmer exhibit a conspicuously striped thorax and abdomen. The striped abdomen especially distinguishes the species from many other species with striped thorax. Mature males, which are the most commonly seen individuals, have a pruinose blue abdomen, black at the tip; brilliant green eyes; and a white face. In drier parts of the West, the thorax also becomes pruinose blue, and mature females may become pruinose.
One of the most common and widespread North American species, Blue Dashers have been seen in fall concentrations of dragonflies on the New England coast. There is no other evidence for migration in the species.
Autumn Meadowhawk (Sympetrum vicinum)
Mature males and some females of this small species are bright red all over, with a fine black line on the top of S9 and red-brown legs. Immatures are yellow to orangish, with yellow legs. Females have a prominent scoop (the subgenital plate) extending under S9. Most other small red dragonflies (several species of meadowhawks) in the same areas have black legs and more extensive black markings on the abdomen; none of the females have an obvious scoop. Mass movements of this species have been observed in fall in New England, but there is no real evidence of latitudinal migration as such.
Great Pondhawk (Erythemis vesiculosa)
Great Pondhawks are unmistakable if seen well. Entirely green with dark bands across the abdomen, they are larger than any other skimmer. They approach darner size, but they are perchers. Males fly over their breeding ponds but eventually land, and when not at breeding sites they are often in open woodland, even in small clearings under the canopy.
Perhaps not a latitudinal migrant, this tropical species has nevertheless been seen in large numbers in directed flights in south Florida and other tropical localities.
Twelve-spotted Skimmer (Libellula pulchella)
This large skimmer is easily recognized by the three large black spots spread across each wing, from base to tip. The thorax is brown with two diagonal yellow stripes on either side, and the abdomen is brown with a yellow stripe along each side. In mature males, white spots appear between the black spots on the wings, and the abdomen becomes pruinose whitish. The only other skimmer in its range with similar large black wing spots is the female Common Whitetail, which has whitish markings on the sides of each abdominal segment rather than a continuous yellow stripe.
Twelve-spotted Skimmers have been seen in southward movements of dragonflies along the Atlantic coast, and there is some indication that they turn up in the South only late in the season, possibly migrants from the north.
Painted Skimmer (Libellula semifasciata)
Painted Skimmers live up to their name, and the wings especially glow with color. A rich brown, the thorax has two whitish to yellow diagonal stripes on each side. The abdomen has yellow edges and a jagged black central stripe on the last few segments. The wings are marked with a brown streak at the base and brown spots at the middle and near the end. The veins along the front of each wing and at the base of the hindwings are largely yellow.
Some Painted Skimmers appear in spring in the northern states and extreme southern Canada before they would have emerged locally, presumably migrants. They have also been observed in autumn along the northeast coast in apparent directional flight.
In addition, there have been reports of migratory flights in still other species, so observers should be on the lookout for such flights, or even individual dragonflies of different species that seem to be associated with migratory flights of the well-known species.