This method is labor intensive and time consuming, but gives you a readily identifiable specimen and a reference exuviae. Another method is to collect the exuviae shortly after natural emergence and attempt to identify them. This has numerous disadvantages, the primary one being that some of the keys don't work. Timing is critical, since you must be at a site near emergence time before the exuviae are washed away by storms. Advantages are that it is non-destructive to the habitat or population of odonates, you don't have to maintain aquaria, feed nymphs, or closely follow the emergence.
Ophiogomphus exuviae are difficult, but less problematical than some odonate groups.
I have had difficulty using these keys, probably due to individual variation. The descriptions used here emphasize some features not used in either of these works. Ophiogomphus colubrinus was collected by Paul Novak in 1995 on the Au Sable River representing the first New York record. I have attempted to facilitate the identification of species by using the shape of the antennae, or in similar species, a combination of antennae and dorsal projections on the abdominal segments. Unfortunately, there can be considerable individual variation, and atypical specimens are not uncommon.