Monday, June 7, 2010

Not all Bluets are blue: Orange Bluet (Enallagma signatum) and Vesper Bluet (Enallagma vesperum)

... with a bad infestation of parasitic mites. An immature female Eastern Forktail looks superficially similar but at 35 mm in length a male Orange Bluet (Enallagma signatum) is a bit longer and has a more slender profile. Also note that abdominal segment S9 is completely orange.

Immature female Eastern Forktail (Ischnura verticalis)

More views of the male Orange Bluet

A closeup of the terminal abdominal segments showing the cerci, S9, and the parasitic mites. I don't know what species these particular hitchhikers might be but it seems that water mites go through some interesting developmental stages throughout their life history. Here is a link to some posts at, and another link to some more reading material on the fascinating life cycle of these small arachnids: Hydracarina. I've noticed water mites in ponds and lakes many times in the past without giving them a second thought. Until today I had no idea that they pass through so many complex changes during their little lives ... you learn something new every day.

The following day I stumbled across this interesting damselfly (also carrying around a load of mites). Immature Orange Bluet males exhibit blue and may be confused with male Vesper Bluets. However, the humeral stripe in a Vesper Bluet is thin and weak ... and indeed, in this specimen it's virtually nonexistent. Based on this I think this damselfly is most likely an immature male Vesper Bluet (Enallagma vesperum), and I'll keep my eyes open for opportunities to photograph mature individuals. This might be tough due to their crepuscular nature and their habit of staying over open water and perching on floating vegetation such as water lilies and pondweed.

About a week later I photographed this teneral Vesper Bluet at the same location. The lack of claspers and the black mark on the dorsal surface of S9 indicate this is a female (in fact the vulvar spine typical of genus Enallagma was visible in the field, and can be seen by zooming in on the lateral view). Again note that the humeral stripe is little more than a rusty smudge; compare this to the conspicuous lines on the thorax of the Orange Bluet.

Hoping to get more photos of mature adults I made a late afternoon trip the lakeshore habitat of these two damselfly species. There were plenty of Orange Bluets active from about two hours before sunset until dusk, but no luck getting a picture of an adult male Vesper Bluet as yet.

Not in its preferred habitat of floating vegetation (it was perching the shrubbery near the pavillion) nor time of day (it was late morning), but the weather was overcast and this female Vesper Bluet was out and about. Again note the blurred humeral stripe, the blue on the sides of S9, and the all blue S10. This damselfly is visibly longer than any other species of local green Enallagma female, with the exception of the easily distinguished Orange Bluet. The small eyespots connected by an occipital bar also make both of these damselflies easy to single out in the field.

A considerable amount of effort and several evenings of wading through leech infested water resulted no images of a mature male Vesper Bluet. As is often the case getting a picture was a matter of luck ... these photographs were taken at about 11:30 am on a bright sunny day, and the insect was perching in the shrubbery, although not too far ashore from its favoured habitat. A striking damselfly, this species is normally seen in the late afternoon or early evening on floating vegetation.