114 DRAGON FLIES VS. MOSQUITOES. 



The dragon flies (Odonata), especially the ^schnina, 

 Gomphina, and Libellulina, are the natural enemies of the 

 mosquitoes ; they are voracious, they sometimes appear in 

 great numbers, and as a matter of fact the mosquito dis- 

 appears before them, while their breeding grounds are in 

 many respects similar, so far as fresh and brackish water 

 habitats are concerned ; and, finally, in the metamorjihoses 

 of the di'agon fly we meet conditions which introduce it 

 in antagonism to the mosquito at the same stages of de- 

 velopment. 



The voracity of the dragon fly has been frequently 

 reported, and it is an old fact that the dragon fly will eat 

 its own body when ofiered to him. I have experimented 

 with ^schna heros, which ate forty flies inside of two 

 hours, while Libellula pulchella devoured twenty-five flies 

 in the same period. 



Migration. 



That the dragon fly does naturally occur in great num- 

 bers at favorable moments is also a matter of scientific rec- 

 ord. Mr. E. T. Koppen (Stett. Ent. Zeit., pages 183-188, 

 1871) gives a chronological resume, from 1494 to 1868, 

 of records of flights and swarms of species of dragon flies, 

 especially Libellula quadrimaculata Linn. (See Appendix B 

 for further information on migrations of dragon flies.) 



That the mosquitoes actually diminish in the presence 

 of the drao-on flies seems in a measure authenticated. Dr. 

 Edgar A. Mearus informs me that while he was stationed 

 at Fort Snelling, JNIinnesota, the mosquitoes appeared in 

 vast swarms, to be shortly after followed by large numbers 

 of dragon flies (L. pulchella ?), at whose appearance the 

 numbers of mosquitoes, which were at that time a pest, 



