70 



short, slender appendages, the antennae or feelers. At the front of 

 the head is a pair of biting jaws or mandibles. These larvae feed on 

 almost any kind of refuse; some have been reared on the sweepings 

 from rooms. There is always some organic matter in this refuse, 

 and this is doubtless their nourishment. The larvae in houses usu- 

 ally crawl into cracks or under carpets and feed on the dust that 

 occurs in such places. Those that infest wild animals probably 

 feed on the refuse in the nests or retreats of these animals. They 

 remain in the larval stage from a week to ten days, sometimes two 

 weeks, molting the skin three times in this interval. Then they 

 spin flat, white, silken cocoons, in which they transform to the 

 pupal stage. Sometimes the cocoon is covered with particles of 

 dust. In from five to eight days the adult flea emerges from the 

 cocoon. The period of their transformation is affected by the tem- 

 perature and moisture. In warm, damp weather a generation may 

 develop in ten days or two weeks, but usually about eighteen days to 

 three weeks elapse from the egg to adult. Although some moisture 



FIG. 6. Flea, showing the various parts. 



seems necessary to their development, an excess is apt to destroy 

 the larvae. 



The leaping ability of adult fleas is familiar to all. No part of the 

 leg is particularly enlarged, so that the jump is made by the entire 

 leg as in the leaf-hopper insects, and not by the hind part of the leg 

 as in grasshoppers and flea-beetles. The size of fleas is not as vari- 

 able as in many insects. Most are about 2 to 3 millimeters long, 

 while the range is about 1.5 to 6 millimeters. The adult flea has a 

 hard, strongly chitinized body. The head is small, and on each side 

 bears a short jointed antenna, which may repose in a groove or 

 depression. Most species have a small, simple eye, but several 

 forms are normally without eyes. The sides of the head below the 

 antennae are called the genae. At the lower front end of the head is 

 the mouth and mouth parts. The latter consist of a pair of trian- 

 gular maxillae with jointed maxillary palpi and a beak or proboscis 

 made up of one median and four lateral pieces. The outer pair of 

 lateral pieces is the labrum with the imperfectly jointed labial palpi. 



