THE ECTOPARASITES OF THE RAT. 



By Nathan Banks, 

 Assistant Entomologist, Bureau of Entomology. 



The ectoparasites of the rat fall naturally into three groups, the 

 fleas, the hce, and the mites. These three groups are widely sepa- 

 rated from each other, the mites belonging to the class Arachnida, 

 having four pairs of legs, no segmentation to the body, no antennae, 

 and no compound eyes. The fleas and Kce belong to the class 

 Insecta. The lice are near the order Hemiptera, sucking insects 

 without a complete metamorphosis, while the fleas are related to the 

 Diptera and pass through a complete metamorphosis. All of these 

 three groups, however, agree in one character — they are wingless. 

 The mites and hce have flattened or depressed bodies, while the fleas 

 have compressed bodies. All three groups have many other species 

 which infest various other animals. Few, if any, of these parasites 

 confine themselves to the rat, and all can walk or jump in the adult 

 condition, so that they can easily transfer their attentions from one 

 rat to another or to some other host. The majority of them are 

 known to occur on mice, and several of the fleas and mites will 

 readily attack man. 



FLEAS— SIPHONAPTERA. 



These wingless, compressed insects are known to all, but few have 

 taken the trouble to look at them with much care. The adult female 

 flea deposits her eggs among the hairs or fur of the host animal, but, 

 unhke the eggs of many parasites, these are not fastened to the hairs 

 and fall freely to the ground. These eggs are oval, whitish, and 

 smooth, and about one-half milhmeter long. The larvae escape from 

 the eggs in two to five days. They are enabled to break the egg- 

 shell by a slender process on the top of the head which disappears after 

 the fijst molt. This larva is a slender, legless, cyhndrical creature, 

 whitish or yellowish in color, with a head and 13 segments. There 

 are a few scattered hairs or bristles on the body and at the tip is a 

 pair of corneous processes. On the upper part of the head is a pair of 



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