196 STUDIES IN INSECT LIFE, ETC. 



undergrowth of a forest. Few grouse are free 

 from these bird-lice, perhaps hardly 10 per 

 cent., and the number on each bird is to some 

 extent a measure of its ill-health. On a healthy 

 grouse perhaps but two or three are found. 

 They are insects with stout and powerful jaws, 

 which they use to bite off the barbules of 

 the feather or the finer plumules which form 

 their sole nutriment. What fluid they obtain 

 to moisten this somewhat dry nutriment is not 

 apparent, but the animals are active and by 

 no means so easy to catch as one at first thinks. 

 They lay very beautiful eggs attached in small 

 groups to the base of the after plume of the 

 feather or between it and the main shaft. The 

 young hatch out as mipiatures of the parents, 

 and there is no metamorphosis. The same species 

 occurs on the Black Grouse and upon the Willow, 

 or Hazel Grouse. On a piner these bird-lice 

 increase enormously in number, and their num- 

 bers to some extent serve as a measure of the 

 gravity of the disease. Both of these bird- 

 lice cast their skin several times ; the exact 

 number of times is, however, not known, but 

 cast skins are frequently met with. The young 

 birds are probably infected with these ecto- 



