It’s Skimmer season! Around here, the dragonflies that are the most common at this point in the summer are the skimmers (Libellula). Identifying them can sometimes be a little challenging, especially the females, so I’ve done another set of comparison charts for these three: Bar-winged Skimmer (Libellula axilena), Slaty Skimmer (Libellula incesta), and the Great Blue Skimmer (Libellula vibrans). The males are relatively easy to identify but the females can be tricky to identify.
The Great Blue Skimmer is the largest of the three and is the largest king skimmer in our area. Males are blue with blue-green eyes and a white face. The Slaty Skimmer is entirely dark slaty-blue pruinoise with a metallic blue face and dark eyes. The Bar-winged Skimmer is pruinose blue with reddish brown eyes and a metallic black face, and it has black bars along the front of the wings. There is a faint whitish area near the body at the base of the hindwing. Those are the males. The females can be quite confusing so I’ll include the comparison chart for them first.
All three are very common here and since they like to perch out in the open (the Great Blue Skimmer is particularly apt to perch out in the open in a spot of sunshine) so they are easy to see.
Here are the females. One thing to note: one of the major things to look for on skimmers is a pale or cream-colored “wolf’s head” pattern on the thorax. If you look closely at these females, you’ll see a cream-colored area that kind of looks like a wolf’s head with the nose pointing to the dragonfly’s head. Some had ears, some don’t and that’s an important thing to note. The shape of the wolf’s head can be quite distinctive and diagnostic for several species. (As a side note: that wolf’s head pattern is also one important factor in separating the Golden-winged Skimmer, Libellula auripennis, from Needham’s Skimmer, Libellula needhami, so it pays to look for it.)
Below is the comparison chart for these three skimmers.
| Characteristic | Bar-winged Skimmer Female | Slaty Skimmer Female | Great Blue Skimmer Female |
| Eyes | Reddish | Red over gray; brown | Dark reddish brown; brown to blue |
| Face | Can be pale | Only top part of face dark, eventually all dark; Dull brown, paler below | Dirty white |
| Thorax | Cream-colored “wolf head”, patterned like male with a pair of triangular dark marks above and to the rear of the legs | Cream colored “wolf head”, more extensive brown under the wings than Great Blue; Brown in front, yellow to gray on sides | Cream-colored on sides and along frontal carina. Most extensive pale color below the wings. Any dark marking under wings only a faint line; “Ear of the wolf head” is missing. |
| Stripes | Broad dark shoulder stripe; Black streak below hindwing broader than in Slaty | Broad dark shoulder stripes extend back below wings. | Brown shoulder stripes wide and extending back slightly below wings. |
| Legs | Black | Entirely black | Pale color basally on femora |
| Wings | Typically clear, dark wingtips | Pronounced basal streak and more extensive dark tips. | |
| Abdomen | Black with markings described below; Black central stripe widens at rear, dark side stripe on basal segments narrows to rear | Paler basally, then black with prominent marks as below | |
| S1 – S2 | Dark lateral bar, yellow with thick black dorsal line | Pale lateral rectangles | |
| S3 | Yellow with thick black dorsal line | Pale lateral rectangles | |
| S4 | Yellow with thick black dorsal line | Yellowish orange lateral rectangles | |
| S5 – S8 | Yellow with thick black dorsal line | Yellowish orange lateral rectangles | Black with prominent lateral yellow-orange rectangles. Small flange on S8. |
| S9 | Yellow with thick black dorsal line | Yellow | Black dorsal stripe widens posteriorly, yellow on sides |
| S10 | All black | Black dorsal stripe widens posteriorly, yellow on sides |
As I mentioned, the males are a little easier to identify.
Here is the comparison chart for the males.
| Characteristic | Bar-winged Skimmer Male | Slaty Skimmer Male | Great Blue Skimmer Male |
| Eyes | Dark reddish brown | Dark brown | Bright blue or turquoise |
| Face | Metallic black | Metallic blue-black | White |
| Thorax | Front of thorax pruinose bluish-white, sides somewhat pruinose | Black, overlaid with dark slaty-blue pruinosity | Pruinose blue |
| Wings | Well-defined basal streak, dark spot at nodus, interrupted dark line along front edge between nodus and entirely dark stigma; narrow dark tip. Extreme base of hindwing pruinose white | Usually clear, may have dark tips and a tiny spot at nodus | Dark streak at base, dark spot at nodus, and faint dark tip |
| Abdomen | Base of abdomen pruinose bluish-white, sides pruinose, top of abdomen is black | Black, overlaid with dark slaty-blue pruinosity | Pruinose blue |
| Overall | Less extensive wings markings than Slaty and never a basal streak | Very large |
This type of comparison chart really helps me understand the differences between species and to (hopefully) correctly identify them. Even with it I make mistakes, but it really does help.
