10 Lake Maxinknckee, Physical and Biological Survey 



ORDER ODONATA 



THE DRAGON-FLIES 



By Charles B. Wilson 

 INTRODUCTION 



Like the May-flies, the Dragon-flies are all aquatic and consti- 

 tute the most important group of insects to be found about the 

 lake. They are also the most attractive and graceful, in spite of 

 the obnoxious name of "snake-feeders," which has been bestowed 

 upon them in the common local vernacular. They have not, of 

 course, the remotest connection with snakes, nor are they poisonous 

 or harmful in any way, as is popularly supposed. They are strictly 

 carnivorous and often cannibalistic in all stages of development, 

 the larger imagos and nymphs habitually eating the smaller ones. 



But they feed chiefly upon other animals such as flies, insect 

 larva?, small crustaceans, worms, leeches, fish-fry and tadpoles. 

 They seem to relish especially house-flies and culicids, and thus 

 become of great economic importance through the destruction of 

 these pests. That the curse of house-flies and mosquitoes is kept so 

 delightfully within bounds at Lake Maxinkuckee is very largely 

 due to the untiring ministrations of the dragon-flies. 



Their eggs are either laid in the water or inserted into the 

 tissues of some water plant or floating fragment. 



As soon as the egg is hatched the nymph begins devouring other 

 animals. Of course, it has to be content at first with very small 

 ones, but as it increases in size and strength it becomes able to kill 

 larger and larger ones until finally it includes small fish and tad- 

 poles among its prey. 



The full-grown nymph of one of the larger dragon-flies is fully 

 two inches in length with a stout muscular body and strong legs. 

 As soon as it is fully matured the nyi.^ph crawls up out of the 

 water on a rush stem, the leaf of a water plant, a stake, a board, 

 or other convenient support, usually during the night or very early 

 in the morning. As soon as it becomes dry the skin splits along 

 the back, and the fully developed dragon-fly emerges. These old 

 nymph skins may be found about the lake during the entire sum- 

 mer, and often in the early morning the newly emerged imago may 

 be seen perched on the skin or close by. Thirty skins were taken 

 one morning from the inside of a boathouse on the west side of the 

 lake. 



That the dragon-flies enumerated in the following list play a 

 very important part in the economy of the fish life of the lake may 

 be seen from several considerations. 



