212 NEW YORK STATE MUSEUM 



4 Aeschna constricta 



The nymphs of this dragon fly live in the midst of the shore 

 vegetation in shallow water. The trout that eat them probably 

 have to go beyond the confines of their usual feeding grounds 

 to get them. The advanced stage of digestion in which the spec- 

 imens were found seemed to indicate that the specimens had 

 been taken during the preceding night. Aeschna nymphs 

 attached to a hook were taken by the trout, but not more read- 

 ily than minnows, small frogs or other bait. 



These were the largest animals the trout had eaten. The vol- 

 ume of one of them would equal perhaps that of 15 to 20 Chi- 

 ronomous larvae, or 30 to 10 Corethra larvae, or 5 to 7 caddis fly 

 larvae, or 4 to 5 Callibaetis nymphs. They are among the most 

 powerful members of the aquatic insect community and clamber 

 -about frequently on exposed places on plant stems, where the 

 trout, if at hand, might easily seize them. 



In a small way the dragon fly nymphs are competitors of the 

 trout for food. They eat small insects promiscuously, and 

 doubtless many pupae of Chironomus and, Corethra fall victims 

 to them. They will eat young trout, also, as long as themselves. 

 I demonstrated this at Saranac Inn by confining thena together 

 in a breeding cage. One little trout would be captured quickly, 

 xind then the others would be wary of the nymphs and keep 

 away from them well^ so that we would think they would evade 

 a similar fate, but one by one they would disappear till all had 

 been eaten. The Aeschna nymph approaches its prey with the 

 slowness and poise and stealth of a cat till within striking dis- 

 tance. Plate 5, figure B, shows a nymph of this species pois- 

 ing for a stroke at a backswimmer (Xotonecta). 



The adult dragon fly is shown also on this plate. Transforma- 

 tion occurs in the latter part of June and in July. The female 

 inserts her eggs by means of an ovipositor into the stems of 

 plants just below the surface of the water. The eggs hatch in 

 about three weeks, and the little nymphs at once take up their 

 abode among the submerged plants and eat promiscuously any 

 other animals they can overpower; they also eat one another. 



