cobra clubtail

LC - Least Concern

N5 - Secure

SNR - Unranked

not listed

Cobra clubtail is a fairly common, medium-sized, semi-aquatic dragonfly. It occurs in the United States east of the Great Plains and in adjacent Canadian provinces. It is found at large rivers with moderate to rapid current, and occasionally at large streams and large, rock-bordered lakes. In Minnesota it occurs along the major rivers, including the Rainy, Red, St. Croix, Mississippi, Minnesota, and Cannon Rivers. Adults are active from late May to early August. They perch on the shoreline on shrubs, rocks, or sand.

Adults are 1⅞″ to 2¼″ (47 to 57 mm) in length and have a 2⅝″ (66 mm) wingspan. The body is black with pale yellow to greenish markings.

The head is small. The face is yellow with a heavy horizontal black stripe. The large compound eyes do not meet at the top of the head. They are bright green in direct sunlight but appear gray in the shade. The area behind the compound eyes at the top of the head (occiput) on both sexes is yellow.

The thorax is black with yellow or greenish (pale) stripes on top and on the sides. On young adults the markings are bright yellow. As the dragonfly ages the thoracic markings fade to a dull grayish-green. The pale stripes on top (dorsal stripes) of the thorax are as wide as the black stripes. They are joined at right angles in front forming a rearward-facing U pattern. There is a narrow stripe in the shoulder area that connects at the rear to the dorsal stripe. The sides of the thorax are pale with two narrow, usually unbroken, black stripes.

The abdomen is slender and black with pale markings. It is very narrow from segments 3 through 6, then expands into a noticeable “club” on segments 7, 8, and 9. The club is broad and is said to resemble a cobra’s hood. This is the feature that gives the species its common name. The upper (dorsal) surface of abdominal segments 1 through 7 have yellow, elongated, triangular spots. The spots of segments 3 through 6 are thin. The spot on segment 7 is broader and short. There are no dorsal spots on segments 8 through 10. There is a bright yellow spot on each side of segments 8 and 9. The lateral spot on segment 8 is small and does not reach the lower edge of the club. On some individuals it may be tiny or absent. The lateral spot on segment 9 is much larger, spanning the entire margin and reaching the lower edge. Unlike the other pale markings, the color of the lateral spots does not fade with age. At the tip of segment 10 the male has a pair of distinctive, widely forked claspers (cerci).

The legs are black.

The wings are clear except for a yellow tinge on the basal quarter and a dark cell (stigma) on the leading edge near the tip.

Total length: 1⅞″ to 2¼″ (47 to 57 mm)

Wingspan: 2⅝″ (66 mm)

Large rivers and streams and large lakes

Late May to early August

Adults perch on the shoreline on shrubs, rocks, or sand.

Sources

4, 7, 17, 18, 24, 29, 30, 82.

Fairly common

This species was formerly classified as Gomphus vastus. In an attempt to clarify the relationships of species in the genus Gomphus (Needham, 1947) , five subgenera were proposed. This species was placed in the subgenus Gomphurus. In later years, several other subgenera were defined. Nine of the genera were grouped in what was called the Gomphus complex. A recent phylogenetic analysis (Ware, et al., 2017) raised all nine subgenera in the complex to genus level, and Gomphus vastus became Gomphurus vastus.

Location: Wagon Wheel Trail in La Crescent