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Identification of Zebra Clubtail

DESCRIPTION: The Zebra Clubtail (Stylurus scudderi) is a large insect belonging to the order Odonata, sub-order Anisoptera (the dragonflies), and family Gomphidae (clubtails). Clubtails are a distinctive group of dragonflies that generally inhabit flowing waters, though they can be found at a variety of habitats, including ponds and lakes. Clubtails also have the distinction of being the only group of dragonflies in Massachusetts to have widely separated eyes. The name clubtail refers to a swelling in the distal segments of these
dragonflies’ abdomens, creating a form not unlike a club that varies in width from species to species. The Zebra Clubtail possesses a rather wide club, nearly as wide as the thorax (section behind the head), which includes the seventh, eighth, and ninth segments (dragonflies and damselflies have ten abdominal segments). The Zebra Clubtail is a very striking insect with black and yellow patterning (which prompted its naming) and bright green eyes. The face is green with black cross stripes. The dark brown thorax has two large buff white stripes on each side. The black abdomen is marked with pale yellow rings. Abdominal segments eight and nine have a large yellowish spot located laterally on each side, while segment seven has a smaller spot in the same location. The three pairs of powerful legs are jet black and lined with spines which aid in catching the small aerial insects these insects feed on. Zebra Clubtails perch horizontally on rocks, logs, vegetation or the ground with their wings held horizontal, like those of an airplane.

Adult Zebra Clubtails range from 2 to 2.3 inches (52 to 59 mm) in length. Although male and female Zebra Clubtails appear similar in their coloration, the female is slightly larger with a reduced “club.”

SIMILAR SPECIES: Although many of the clubtails are similar in appearance, the Zebra Clubtail is a large and distinctively marked species. A combination of factors, including its ringed abdomen, green eyes, terminal abdominal appendages (males), hamules (males) and vulvar lamina (females), help to easily distinguish this species from all other dragonflies in Massachusetts (Needham et al. 1999). The nymphs can be distinguished by characteristics of the abdominal segments and palpal lobes as shown in the keys in Walker (1958) and Soltesz (1996).

HABITAT: Zebra Clubtails inhabit medium-sized forested streams which usually have some intermittent rapids. These streams are generally sandy-bottomed with slow to moderate flow. Elsewhere within its range, the Zebra Clubtail has occasionally been found on large lakes.

LIFE-HISTORY/BEHAVIOR: The Zebra Clubtail is a late flying species. Emergence in Massachusetts probably occurs in early July. Following maturation, which may take a week, Zebra Clubtails can be seen at breeding habitat from mid-July through early September.

Dragonflies are an understudied group of insects. As a result there has been little published on their habits and general life histories. This is true for the Zebra Clubtail, for which there is a paucity of published material. However, information that has been published on other related species is most likely applicable.

During their complete life cycle, dragonflies go through two distinct stages, a nymph stage where they are wholly aquatic, and an aerial adult stage. Zebra Clubtail nymphs spend much of their time buried in the sand at the bottom of their stream habitat where they wait to ambush almost any animal that is a suitable size.