Length: typically 80 - 85 mm
The dragonhunter is the largest member of the clubtail family. As its name implies, it is a bold predator. Dragonhunters often capture dragonflies nearly their own size. They also prey on butterflies, like the hapless monarch shown here, and other large insects.
The eyes are green and widely separated. The face is yellow, and the overall size of the head is small compared with the robust thorax. Males and females are similar in color and markings.
Dragonhunters favored perches are along streams, although they may also be found some distance from water.
Males have a distinctive flight posture, with the abdomen often curved under so that the profile is that of the letter "J."
White and Sexton (1989) studied the predation of Hagenius brevistylus on monarch butterflies, stating that they knew of no other records of an invertebrate that preys on monarchs. Monarchs have unpalatable chemicals (cardenolides) sequestered in their bodies, and these chemicals ensure that predators leave them alone (or taste them only once).
White and Sexton showed how the dragonhunters use their legs to rotate the monarch, eating primarily the thorax where the cardenolides are not so noticeable. Dragonhunters may eat the Monarchs abdomen, too, but will stop eating once they come to a significant amount of cardenolides. The dragonfly always fails to eat the Monarchs wings, since the level of unpalatable chemicals is very high there.
While the study did not claim that monarchs are the only prey of Hagenius brevistylus, the authors did state that in times of monarch abundance Hagenius brevistylus seemed to feed on monarchs alone. Monarchs apparently have learned to modify their behavior to avoid dragonhunter predation. Though monarchs are normally a sun-loving species, when dragonhunters were around the monarchs fed primarily in the shade, or if they were in the sun they flew to the shade if disturbed. Dragonhunters almost invariably hunt in the sun.
The yellow stripes are thin on the dorsal surface of the thorax, but thick on sides of the thorax. The eyes are green and widely separated. The face is yellow and may have a black stripe.
The club on this member of the clubtail family is relatively modest. Yellow spots adorn the sides of the abdomen.
Markings on the top of the abdomen are spare. Typically these include thin yellow lines on top, and a yellow spot on segment eight.