' TNTRODUCTIOxN. 



A NUMBER of years ago, while engaged in building 

 the Lake Superior and Mississippi Railroad, I made fre- 

 quent excursions, in the capacity of director and treasurer 

 of the company, through the swampy forests around the 

 head of the great lake. Sitting in camp at supper time, 

 I often, with a sentiment of gratitude, looked through 

 my mosquito veil at the dragon flies that collected in the 

 open spaces among the pine trees. They darted from 

 side to side, like swallows in a meadow, but with amazing 

 rapidity ; and at every turn, the natives assured me, a 

 mosquito "ceased from troubling." Afterwards I haj)- 

 pened to observe an entomologist feeding a dragon fiy 

 that had eaten thirty house flies in rapid succession with- 

 out lessening its voracity. What thought could be more 

 natural than the one that came to me, that an artificial 

 multiplication of dragon flies might accomplish a miti- 

 gation of the mosquito pest. The proposition was >o 

 evident that I sought among entomological works for 

 some account of experiments tending to throw light on a 

 subject of such enormous practical importance, but with- 

 out result. Then followed consultation with men eminent 

 among specialists wdiose lives are spent in the study of 

 insects, and to my surprise the fact was developed that 

 science had left almost untouched those investigations into 



