PHYLUM ARTHROPODA — CLASS INSECTA 321 



prey. The adults are swift flying, brightly colored, predaceous in- 

 sects. Their food consists of mosquitoes, gnats, and many other kinds 

 of flying insects. Much has been written on the dragonflies of the 

 United States. About twenty-eight hundred species have been de- 

 scribed. The order is divided into the suborders, Zygoptera (damsel 

 flies), and Anisoptera (dragonflies). There are two families of 

 damsel flies, the Agrionidae and CaenagTionidae ; also two families 

 of dragonflies, Aeschinidae and Libellulidae. The beautiful ruby 

 spot, Hetaerina americana Fabr; and the stalked-winged, Lestes 

 uncatus Kirby are damsel flies that are widely distributed. The 

 dragonflies Lihellula pulchella Drury and Sympetrum ruMcund^dum 

 are common west of the Mississippi River in the United States (Fig. 

 184). 



Order Ephemerida. — The Mayflies are aquatic insects, with man- 

 dibulate naiads, but since the adult stage lasts but a day, the mouth 

 parts are vestigial. The adults have well-developed wings and two 

 or three long abdominal cerci. The life cycle occupies from one to 

 three years. The food of the naiads consists of small aquatic plants 

 and organic matter which is obtained from the rocks and mud on 

 the bottom of streams and along the shores of lakes where they live. 

 They serve as food for larger insects and fishes. The prickleback, 

 Ephemerella grandis Eaton; and the western bunchgill, Siphlurus 

 occidentalis Eaton are common species. 



Order Plecoptera (Stone flies). — The stone flies are found near 

 streams, flying low over the water. They have mandibulate mouth 

 parts, four wings that are not so thickly netted with veins as are 

 the Odonata, but with longer antennae than the Odouata. They 

 are found on stones along lakes and streams where they pass their 

 naiad stage. They require running water that is well aerated. 

 Their food consists largely of aquatic insects, such as May flies. 

 They are sometimes used as bait for trout. There are four families : 

 the little curler, Pteronarcella hadia Hagen ; and Perla modesta Banks 

 are representative species. 



HOLOMETABOLOUS INSECTS WiTH COMPLETE METAMORPHOSIS 



The following are some of the important orders that fall within this 

 group. 



Order Trichoptera (Caddis flies). — This order includes about 

 eighteen hundred species of "case flies" or "rock rollers," as they 



