Northern Bluet (Enallagma annexum)

Formerly known as Enallagma cyathigerum and its range believed to to be circumpolar, recent research indicates that the North American and Eurasian lines of this bluet diverged 250,000 years ago and the North American stock now goes by the epithet Enallagma annexum.

Northern and Boreal Bluets cannot be reliably distinguished in the field by sight and it's necessary to examine the male's terminal appendages or the females mesostigmal plates. A tandem pair of Northern/Boreal Bluets – both species have large postocular spots and tapering humeral (shoulder) stripes.

A dorsal view of a typical Northern/Boreal Bluet female – the paired blue spots on S8 may be fused in some individuals. The females can be either blue or tan.

The cerci of the male Northern Bluet are sharply upturned at their lower tips.

Terminal appendages of the Boreal Bluet – the cerci are rounded and angled downward.

The Vernal Bluet (Enallagma vernale) must also be examined in the hand to separate it from the Northern Bluet, the cerci of the male Vernal Bluet have a ridge. There's no way my camera will pick up that kind of detail but it should be visible with a 20× loupe, and thus far I have found no evidence of Vernal Bluets flying in my area.

As of this writing I'm uncertain whether the Vernal Bluet is considered a subspecies of the Northern Bluet (according to my field guide there is evidence of hybridization) or has been elevated to species level.

Boreal Bluet (Enallagma boreale)

Without having examined the claspers it's equally possible that this is a Northern/Vernal Bluet (Enallagma cyathigerum ssp.). This damselfly complex may be distinguished from other "blue type" damselflies, such as the Familiar Bluet, by the large ocular spots and relatively narrow humeral stripe. And although the cerci cannot be seen in detail in lateral view they are clearly much shorter than would be expected on a Familiar Bluet. However, the aberrant longitudinal spot on S5 isn't shown in either of my field guides. This damselfly is about 30 mm long.

Since the mesostigmal plates weren't examined this female could be either a Boreal or a Northern Bluet. We do know it's one or the other because, in addition to the large eyespots and tapering humeral stripe, blue-type females of these two species have a blue spot on the side of S8, often fused at the top as in the damselfly below.

The colors and patterns on the following damselfly are the same as the insect above. This time I was able to take a closeup of the terminal abdominal segments before the damselfly took flight.

This is a Boreal Bluet (Enallagma boreale). The cerci or upper claspers on a Northern/Vernal Bluet would have a hook sharply upturned at the tip.