HOUSEHOLD AND CAMP INSECTS 33 



species appear in large numbers at about the same time each year, 

 and in the Adirondacks one may roam "in woods in early August 

 comparatively free from black flies and yet find hosts on ascending 

 some of the higher mountains. This is due to the fact that the de- 

 velopment of the flies is later at the greater elevations. 



Experiments in recent years have demonstrated the practicability 

 of destroying these larvae in streams by applying an oil preparation 

 such as Phinotas oil. This is heavier than water, settles to the 

 bottom, and a film of oil may be found upon stones 48 hours after 

 application. Black -fly larvae may be killed one-eighth of a mile 

 below the point of application. The one objection is that fish may 

 also be destroyed unless this compound is used in small quantities. 

 The larvae can be swept from rocks, in case treatment with 

 chemicals is impracticable, and after dislodgment caught and re- 

 moved on a wire netting. 70 



Floods, as has been observed in the South, are favorable to black 

 fly development ; consequently a judicious regulation of stream flow 

 has an important effect in reducing the numbers of these pests. 



Stock in badly infested regions may be protected by blankets, 

 smudges or repellant applications, a number of which are given on 

 page 78. 



FLEAS 

 Pulex, Ctenocephalus et al. 



The more common flea about dwellings in the eastern states is 

 the cat and dog flea, 71 while on the Pacific coast the human flea T2 

 is the troublesome species. 73 These insects occur upon their hosts, 

 and according to the investigations of Doctor Mitzmain, 74 the 

 human flea appears to pass a portion of the winter on dogs. There 

 are numerous species of fleas, most of them closely restricted to 

 certain hosts, and a few, as will be seen below, are important car- 

 riers of disease. 



The minute white eggs of fleas are dropped mostly about the 

 sleeping-places of their hosts, and the slender, active larvae feed 

 upon the organic matter found in the dust. They are particularly 

 likely to thrive in cracks and crevices of floors. The egg stage of 

 the cat and dog flea may last 2, weeks, the larval period 12 days, 

 and the pupal period 10 to 16 days, making a total for the complete 



70 Weed. U. S. Dep't Agr., Div. Ent, Bui. 46, p. 108-9. 1904. 



71 Ctenocephalus canis Curtis. 



72 Pulex irritans Linn. 



73 Mitzmain. Pub. Health Bui. 38. 1910. 



74 Pub. Health Bui. 38. 1910. 



