48 



variety of waters containing vegetation, and even where other 

 species of nymphs are largely wanting. Lakes, rivers, ponds, 

 swamps, transient pools, small ditches, springs, throughout the 

 state, — all produce a crop of these nymphs. This fact together 

 with their active habits and voracity, would indicate a rapid 

 development. Kellicott states that from an excavation for an 

 artificial lake, which was filled up with water in early May, 

 large numbers otJiuiiusuYia^gos emerged in late August, indicat- 

 ing the occurrence of two broods in a year. This is confirmed 

 by one of our experiments, half-grown larvie placed by Mr. 

 Hart in a breeding-cage June 16 reaching the imago stage 

 August 4. A noticeable reduction in the number of large 

 nymphs and an increase of the younger ones about July 1 has 

 been recorded in two different years. Young predominate in 

 our October collections, and those taken early in spring are 

 mostly of large size. The imagos attain greatest abundance in 

 May. On May 19, 1894, the abundance of fresh exuviae was con- 

 sidered worthy of record. 



According to Kellicott this is the first dragon-fly abroad in 

 early spring, remaining until the middle of October. Several 

 pairs were seen by him flying in union March 21, the female 

 ovipositing. In early spring, according to Mr. Needham, the 

 eggs are deposited in the water-soaked stems of reeds, in float- 

 ing sticks, pieces of board, etc.; while later in the season they 

 are placed in the green and growing stems of aquatic plants. 

 He states that the females are usually held by the males during 

 oviposition, and often descend into the water for this purpose. 



The imagos wage a ceaseless warfare on gnats, mosquitoes, 

 and other small winged insects. In August, wi'ites Mr. Need- 

 ham, I saw a small swarm (more than a score) moving together 

 through an orchard in Cass county. 111., miles from open water. 

 At the same place a few days later, during three successive 

 days of high wind, Aiiax Jioi/KS and TnuHca lacerata could 

 always be seen hovering in the lee of orchard trees, grape 

 arbors, stacks of grain, etc., circling swiftly several rods away 

 from shelter then beating slowly toward it again, head to wind. 



