The live insect display at the 2015 Fly Symposium included many species and numerous specimens, including Gomphus dragonfly nymphs. At the completion of the show, all of the insects were transferred to an aquarium for observation and photos.
The Gomphus nymphs were only visible occasionally during daylight. They remained hidden under rocks, branches and weeds. During darkness, they fed on other small nymphs such as mayflies and caddis flies.
Some of the Gomphus emerged in April. Prior to emergence, it was noted that the nymph was very active for 24 hours. There was no attempt at concealment. They were in a fast swimming mode, almost constantly. When given a means of crawling out of the water onto a rock or branch, they remained close until ready to emerge.
This behaviour relates to fly fishing. Normally, one doesn’t see free swimming Gomphus nymphs in a lake. The are hidden in the bottom structure. Also, the trout are not constantly feeding on the nymphs, as evidenced by stomach contents. However, when the nymphs are free swimming, prior to emergence, they become a significant menu item. During this period, the fish gorge on the nymphs. Numerous stomach samples reveal a predominance of Gomphus nymphs during this pre emergence period.
The attached slide show illustrates another marvel of nature where a rather ugly looking Gomphus nymph is transformed into a graceful winged adult dragonfly. All of the photos are of the same nymph. The entire emergence took 2 hours.