130 OUTLINES OF ENTOMOLOGY. 



somewhat triangular in shape, while the hind wings are scarcely one- 

 fourth their size, and nearly circular. The legs are slender, the front 

 pair longer than the others. The abdomen tapers backward, and ends 

 in two or three bristle-like appendages that are twice or three times 

 the length of the body. The eggs are simply dropped into the water 

 in a mass. The young feed upon minute aquatic vegetation or prey 

 upon microscopic animals. Some species, whose habits have been 

 studied in aquaria, have been observed to molt more than twenty 

 times, and to require from one to three years in which to complete 

 their growth. Among other anomalous characters found in these lar- 

 vae are a pair of large tracheal gills attached to the under side of the 

 head. Another singular phenomenon occurs in these insects namely,, 

 the molting of the perfect insect. The first winged form is called the 

 sub-imago. This rises into the air, but after a short flight settles upon 

 some object and rapidly sheds its skin, wings, legs, caudal bristles and 

 all, leaving behind it the filmy integument of the sub-imago. 



The Stone flies (Perlidce), so called because the young are com- 

 monly found under stones in running water, are much larger than the 

 May flies, and resemble, in general form and structure of the body 

 and wings, the Hellgrammite fly, although none of the species are so 

 large as the latter. The hind wings are also proportionately much 

 broader, and have few cross-veins. Some very minute species appear 

 very early in the spring, and are called Snow flies, being often coinci- 

 dent with late snows. 



The Termites or white ants abound chiefly in tropical regions, 

 where they are excessively destructive and difficult to contend with. 

 A few species also occur in temperate climates, and one, Termes flavipes, 

 is found in all parts of the United States, and often does much damage 

 to the sills of buildings and wooden sidewalks, to fence posts and 

 similar property. In the Southern States it also occasionally attacks 

 the roots and trunks of orange trees, and the roots of Pampas grass. 

 It feeds, however, by preference upon dead wood, and works so in- 

 sidiously that its presence is not even suspected until the walls of a 

 building give way, or an article of furniture drops in pieces upon being 

 moved. Like the true ants, the Termites are social insects, and live in 

 exceedingly populous colonies. In the tropics many species are mound- 

 builders, erecting conical structures of earth or wood fiber, held in 

 place with cement, that are from eight to ten feet high. All the more 

 northern species are more secluded in their habits, avoiding the light 

 and excavating chambers deep in the earth or in the centers of the 

 largest stumps. From these, under-ground passages and tunnels ex- 

 tend for hundreds of feet in every direction. They are all small insects 



