Eastern Forktail

Eastern Forktails are widely distributed and abundant in the North America—yet I always have found them to be perplexing to identify. Field marks for the male above include the greenish sides of the body and eyes, coupled with the two blue bars on the sides of the blue-tipped abdomen. The first and last photos are taken this summer from Carleton College’s Lyman Lakes. The middle photo, taken in June 2011, is from Carleton’s Lower Arboretum.

Females begin life as orangish bodies (above) but become pruiose (bluish-gray), like the damselfly below. Females only mate once, unusual for damselflies (Dubois). Other females look like males (andromorphs) (Paulson). Larvae go through about a dozen stages (instars) and winter in one of their later stages.

It seems like more often than not, when I encounter a damselfly, it proves to be an Eastern Forktail. This species is found across the northern United States and parts of southern Canada. Eastern Forktails are replaced by Western Forktails across much of the West. The two species are difficult to distinguish—as are several other forktail species.

Tule Bluet

Tule Bluets may at first seem similar to the Stream Bluets that I wrote about in my previous post. Note, however, the broader blue rings on the abdomen, rings that become thinner as you look down the abdomen. The first segment is nearly all blue except for the black spot on the top. The last two segments are almost completely blue. Finally, the cerci at the end of the abdomen are white-tipped (see bottom photo).

Duboiswrites that Tule Bluets are found along the shores of “larger, deeper lakes.” Indeed, I found this individual along the shore of Circle Lake, one of the larger lakes in northern Rice County. He also comments that Tule Bluets deposit their eggs on submerged plants and, also, sometimes on rushes even a foot above water. Larvae live for over a year, go through almost a dozen stages (instars), and overwinter in one of their later instars.

The species is common across northeastern and western North America south to Baja California.

Stream Bluet

Stream Bluets are abundant damselflies. Pairs and single bluets often hover above creeks, like the small stream that drains Lyman Lakes in the Carleton College Arboretum. Pairs often copulate for and hour or two. Males often remain attached to females as they deposit their eggs, sometimes even ovipositing under water for up to 30 minutes (Paulson).I have previously posted photos of mating Stream Bluets.

This species is identified by its relatively broad, black thorax stripes, mostly black abdomen with thin blue rings, and all blue terminal abdominal segment but black-topped, blue eighth segment. The greenish color on the eyes also serves to identify Stream bluets (see bottom photo). The species is found in eastern North America, the eastern Great Plains, and south into eastern Mexico.

Savannah Sparrow

I encountered this Savannah Sparrow singing away on top of a road sign at Circle Lake in Rice Co., Minnesota. The species is abundant across much of North America. Alexander Wilson named this sparrow for where the first specimen was collected—Savannah, Georgia.

Annual mortality of adults is around 50% a year. Nevertheless, most Savannah Sparrows return to where they hatched. The result is relative reproductive isolation, which results in marked geographic variation—17 subspecies are currently recognized by ornithologists (Wheelwright and Rising 2008). Birds breeding here in southeastern Minnesota appear to be heavily streaked with relatively indistinct yellowish lores.

Eastern Pondhawk

The beauty of the emerald Eastern Pondhawk stuck me as I strolled through Erika’s garden last week. These dragonflies are fierce predators (see past post), even consuming fellow odonates. Meadreports that they will even follow people, preying upon their attending mosquitos and blackflies.

Pondhawks are also quite common (even “superabundant,” according to Paulson). Their clutch size averages 900 eggs, all laid in under ten seconds (Paulson). Nymphs must lead a perilous existence, or we would be knee deep in pondhawks. They prefer still water.

Male Eastern Pondhawks start off as relatively dusky creatures. They become pruinose, beginning at the tip of their abdomen, and later, like the one in the last photo, this pruinosity spreads across most of their body.

Four-spotted Skimmer

I have seen Four-spotted Skimmers before, but this is the first from Erika’s garden. On Monday, several flew over the garden. They are fierce predators, even taking other dragonflies. In the garden they definitely behaved territorially, with individuals repeatedly landing on the same stretch of clothesline.

Some males of this species become “satellites” to territory holding males. The satellites are subordinate to the territory holder, but don’t breed unless the skimmers are abundant (Paulson). Field marks include the four spots on the wings and the dark “saddles” at the base of the hind wings.

Green Heron

A week has passed since I posted a bird photo on my blog—must be the summer doldrums. Add another Green Heron to my collection of photos of this species. We found this individual in the northwest Minneapolis metro area during a recent water garden tour. A relatively good picture (if I do say so), especially considering the distance this bird was from me. As typical for the species, this bird remained at the same spot, as apparently the prey was plentiful.

This Green Heron fed in a manner common to the species. It crouched, with the body horizontal, and with a retracted head and neck. With a lunge, and a strike of its bill, the prey (in this case a bullhead or perhaps a crayfish) was taken in its bill (rather than speared). According to Davis and Cushlan, Green Herons are “carnivorous, typically a fish-eating species, despite comments to contrary in literature. However, prey selection is broad, depending on availability, and includes all sorts of invertebrates."

Blue-tipped Dancer

Female Blue-tipped Dancers come in brown (first photo) and blue (second photo) phases. Note the blue tip to their abdomens and, in the blue form, the azure triangle at the rear of the black side stripe. Why do the females come in different morphs? In some damselflies, some females look like males (andromorphs), apparently to reduce male aggression towards them. But, in the case of Blue-tipped Dancers, neither morph looks like the male. One hypotheses is that the two morphs suffer different reproductive and predation rates. If one morph has a high reproduction rate but is often taken by predators, a second morph, with lower reproduction, but less likely to die from predation, may result in both morphs coexisting.

Males (final photo) are a little easier to identify—they are the only dancers with violet, black, and white thoraxes. Notice the male in the last photo is munching on a winged insect. Why don’t males come in two morphs? Scientists suspect that the females are more exposed to predation than their mates (Cordoba Aguilar), thus giving them added advantage to being polymorphic.

Common Whitetail: The Road to Pruinosity

One can hardly write about dragonflies without mentioning pruinosity, as I have done last July when blogging about Powdered Dancers last July. This year Erika’s garden has been full of Common Whitetails. We have counted up to 13 at once as the dragonflies basked on the warm side of our house.

Male Common Whitetails’ abdomens become Pruinose. Pruinosity is a powdery pigment “bloom on odonates that exudes from the cuticle and turns it light blue, gray, or white…” (Paulson). Pruinosity often reflects ultra-violet light. Pruinosity is more prominent on mature individuals and more often on males. The first three photos show Common Whitetails in various stages of becoming pruinescent. The last photo shows an unpruinescent female whitetail—similar to the female Twelve-spotted Skimmer (which has a yellow striped, rather than spotted, abdomen.

Common Whitetails make use of pruinosity for species and sex recognition, for making territorial displays, and, perhaps, to cool their bodies by reflecting solar radiation.

Robberfly

About a thousand species of Robberflies (Family Asilidae) inhabit North America (Maxson). The family has a worldwide distribution. Some, especially in the genus Lapria, mimic bumble bees (Bugguide). Looking like bees may frighten off potential predators, or make it easier for the robberfly to capture the bees. They also prey upon other arthropods, like flies, grasshoppers, beetles, moths and butterflies, and even dragonflies (Ecobirder). The robberfly bite paralyzes their prey, which is then injected with enzymes that digest the prey’s insides. The robberfly then drinks this soup by sucking it through their proboscis.