Total length: 47 - 57 mm
Gomphus vastus, the cobra clubtail, is found in the eastern United States (west to the Great Plains states) and in the far south of eastern Canada (west to Manitoba).
This species is one of the darkest Nearctic clubtails, with less yellow on the dorsum of the abdomen than is present in other species. The yellow on the abdomen that is present (segments 3-7) forms dashes rather than a continuous line. On the club there are lateral yellow spots on S8 and S9, the latter spot running the full length of the segment.
Females differ from the above description by having more yellow on the dorsum and sides of the abdomen. Also, in females there is a very small, pointed tubercule beside each lateral ocellus (Paulson 2011).
The common name comes from the club resembling a cobra's hood.
Males sometimes perch with the abdomen raised as if to show off their "cobra's hood."
Females oviposit while flying, going down to the water's surface at intervals and touching her abdominal tip to the water's surface (Paulson 2011).
Photo data: 14 June 2021. Kankakee River State Park, Kankakee County, Illinois.
GPS data: 41.2133, -88.0274. Elevation 198 meters above sea level.