Dragon-flies and Damsel-flies 81 



the thorax is translucent green or blue, and the long symmetrical body is 

 warm red or deep blue or purple or green. It is often covered with a soft 

 whitish "bloom," that tones down the brilliant metallic iridescence. But 

 as the body dries, the colors fade. They are due not so much to pigment 

 as to the interference in reflection of the various color-rays, this interference 

 being caused by the structure of the body-wall. Just as soap-bubbles or 

 weathered plates of glass or mica produce brilliant colors by interference 

 effects, so does the semi-transparent laminate outer body-wall of the 

 dragon-fly produce its fleeting color glories. While the wings of many 

 kinds are clear, unmarked by blotches or line, the wings of others bear a 

 definite "picture" or pattern, usually light or dark brown or even blackish, 

 reddish, thin yellow, or whitish. These wing-patterns make the determination 

 of many of the dragon-fly species a very simple matter. 



When the dragon-flies go winging about over ponds and streams they 

 are engaged in one of three things: in eating, in mating, or in egg-laying. 

 The prey of the dragon-fly may be almost any flying insect smaller than 

 itself, although midges, mosquitoes, and larger flies constitute the majority 

 of the victims. Howard says that the voracity of a dragon-fly may easily 

 be tested by capturing one, holding it by its wings folded together over its 

 back, and then feeding it on live house-flies. Beutenmuller found that 

 one of the large ones would eat forty house-flies inside of two hours. Howard 

 says that a dragon-fly will eat its own body when offered to it (query, to 

 its head ?) and that a collected dragon-fly, if insufficiently chloroformed and 

 pinned, will when it revives cease all efforts to escape if fed with house-flies, 

 the satisfying of its appetite making it apparently oblivious to the discom- 

 fort or possible pain of a big pin through its thorax. That dragon-flies 

 are sometimes cannibalistic has been repeatedly confirmed by observation. 

 The nymphs have been seen to devour nymphs of their own and other 

 species; the nymphs of a European form have been observed to come out of 

 water at night and attack and devour newly transformed imagoes of the 

 same species, while several instances are recorded of the capture and devouring 

 of an imago of one species by an imago of another. 



The good that is done by dragon-flies through their insatiable appetite 

 for mosquitoes is very great. Now that we recognize in mosquitoes not 

 only irritating tormentors and destroyers of our peace of mind, but alarm- 

 ingly dangerous disseminators of serious diseases (malaria, yellow fever, 

 filariasis), any enemy of them must be called a friend of ours. A prize was 

 once offered for the best suggestions looking toward practicable means of 

 artificially utilizing dragon-flies for the destruction of mosquitoes and house- 

 flies, but no very efficient improvement on the dragon-fly's natural tastes 

 and practices were brought out by this essay competition. 



In Honolulu, the principal city of our mid-Pacific territory, the mosqui- 



