FLEAS. 5 



there is a tendency for the young and, of course, the resulting adults 

 to concentrate in the vicinity of the sleeping places and most fre- 

 quented haunts of the host. This serves the fleas in three ways: (1) 

 By giving them the protection of the bed of the animal in which to 

 develop; (2) by furnishing food to the young in the form of partly 

 digested blood excreted by the adults while on the host; (3) by keep- 

 ing these parasites concentrated where they can easily secure access to 

 the host when they become mature. This habit is also important 

 when we attempt to control the fleas and is referred to again under 

 that topic (pp. 25-28). 



The number of eggs deposited by a single female and the rate of 

 deposition undoubtedly vary largely with the species, the abund- 

 ance of food, and climatic conditions. Prof. Bacot, of the Lister 

 Institute, London, in his extensive studies of fleas has conducted a 

 number of experiments bearing on this point. The number of eggs 

 deposited daily is small, but deposition may continue for many 

 weeks. Bacot records 448 eggs as the greatest number observed by 

 him to have been deposited by a single female of the human flea. In 

 some of these experiments he found that the female would continue 

 to deposit eggs for a period of over three months. 



THE LARVA. 



Within from 2 to 12 days, depending on temperature and moisture 

 conditions, the eggs hatch into minute, whitish, legless, and eyeless 

 maggots. These are not parasitic, but move about actively in the dust 

 and debris in or near the nest of the host. Under favorable condi- 

 tions the growth of the larvae is rather rapid. Flea larvae usually 

 molt twice. The larva? of the dog flea may molt three times, accord- 

 ing to observations made by Mr. Theodore Pergande, of the Bureau 

 of Entomologjr. The first molt takes place in from 2 to T days after 

 hatching, the second from 2 to 6 days later, and the third about 5 days 

 after the second. The shortest larval period observed in these experi- 

 ments was 7 days. In England Mr. Bacot found that the - larval 

 period in the dog flea ranged from 11 to 142 days ; in the human flea, 

 from 9 to 102 days ; in the European rat flea, from 15 to 114 days ; and 

 in the Indian rat flea, from 12 to 84 days. Food, humidity, and tem- 

 perature are all important factors in influencing the rapidity of de- 

 velopment. The larva?, or maggots, are slender, and each joint is pro- 

 vided with a number of hairs or bristles which assist it in crawling. 

 The head differs slightly in appearance from the other segments and 

 bears some of the usual head appendages with which most insects 

 are supplied. These include short, stout antenna?, or feelers, and a 

 pair of mandibles fitted for biting. The top of the abdomen is pro- 

 vided with two fleshy fingers which aid the larva in its movements, 



