Dragon-Flies 



the majority could all the more easily be noticed from the very 

 regular and swift course they generally pursued; but even these 

 few stray ones would soon fall in with the rest again. Very few 

 were seen alighting, and all carefully avoided any movable obsta- 

 cles." This migration was probably caused by the very dry 

 season which had resulted in the drying up of ponds and 

 swamps, and it is probable that other similar recorded migrations 

 have arisen from the same cause. 



Among the insects killed by dragon-flies there must be, of 

 course, some mosquitoes, although the beneficial work of these 

 insects in this direction is greater in the larval stage than in the 

 adult. Dragon-flies are day flyers, but in cloudy weather and 

 toward evening many mosquitoes are undoubtedly killed by them. 

 Dr. E. A. Mearns, U. S. A., (quoted by Beutenmuller) states that 

 at Fort Snelling, Minn., mosquitoes appeared in vast swarms, and 

 were soon followed by large numbers of dragon-flies after which 

 the mosquitoes were considerably reduced in numbers. Dr. 

 Robert H. Lamborn, noticing in the Lake Superior region the 

 activity of dragon-flies in this regard, years later offered a prize 

 for the best essay on the artificial multiplication of dragon-flies 

 for the destruction of mosquitoes and house-flies. The prize 

 essays by Mrs. Carrie B. Aaron, Mr. Archibald C. Weeks, and Mr. 

 William Beutenmuller were published in 1890 in a very readable 

 and valuable book, but as might have been foreseen the practical 

 value of Dr. Lamborn's suggestion was not substantiated. 



The eggs are laid either in the water or are inserted in the 

 stem of some aquatic plant. 



In the dragon-flies of two families there is no apparatus for 

 the insertion of eggs into plant stems, and they are therefore 

 either dropped loosely in the water or attached to submerged 

 objects by means of a mucilaginous substance which surrounds 

 them. With others, however, there is a curious modification of 

 the end of the body. The sides of the vulva are pointed or 

 roughened, and cut into plant tissue so that the eggs may be 

 pushed into the cuts. Here the female gradually crawls down 

 the stem of a water plant until she is often completely submerged. 

 She is always incased with an air film so that she can continue 

 to breathe under water to a certain extent. The number of eggs 

 is variable, but is usually large. Some very curious Hymenop- 

 terous parasites live in the eggs of dragon-flies. 



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