1007.] NATURAL SCIENCES OF PHILADELPHIA. U 



Cowcii. 1 hav(> also nu'iitioned this louse on p. 17 (tf the 1901 report 

 of the same station. This form varies enough from cooleiji to be con- 

 sidered a distinct species; but as these two seem to owe their differences 

 to an alternation of food })lants, I have thou.cht best to con-idcr the 

 foi-ni upon red lir a variety of coolciji. 



Life History. — The winter is spent as minute black lice, each being 

 surrounded with a halo of white waxy threads and resting upon the 

 upper surface of a leaf. They often occur in a line along the median 

 groove. A few warm days al^out the last week in March or the first 

 week in April cause the lice to grow, excrete drops of nectar, and burst 

 the old larval skin. This first spring moult takes place at Fort Collins 

 al^out April 1st. The hibernating form is shown on Pis. V and \I, 

 figs. A and A^ As soon as the old skin has been cast, little patches of 

 white secretion begin to appear along the dorsal surface, and in a few 

 days more the entire body will be hidden by long curled threads of this 

 material. About the 20th of April egg-laying begins, though not all of 

 the lice develop together, and the time of the first egg-laying varies 

 with the earliness of the season. From twenty-fi^•e to forty light yellow 

 eggs are laid by each louse, and these hatch freely just as the new leaves 

 begin to open at the ends of the twigs, and nearly all are hatched by the 

 last of iMay. The lice migrate on to the new growths, insert their setse 

 into the tender leaves and begin to feed and grow, and apparently 

 they never change their location afterwards. This first brood from 

 eggs for the year is dimorphic, in that about one-half remain wingless 

 like the preceding generation, while the other half develop wings. The 

 adults of the alate form appear about June 10; the wingless ones lay 

 eggs like their predecessors, and the young hatching from them, for the 

 most part, insert their setse in the leaves, take on a dark color, secrete a 

 little of the white waxy material about themselves and upon their backs, 

 and so remain until the following spring before growing perceptibly in 

 size, and then become stem-mothers; but those that acquire wings all 

 leave the red fir and, so far as I have been able to trace them, settle 

 upon the leaves of the blue spruce {Picea parrycma), though it is prob- 

 able that they do settle on Engelmann spruce as well. Some of the 

 apterous females continue to develop and lay eggs, especially in shady 

 places and upon tender new leaves, until late in July or even longer; 

 but for the most part development closes with the young hatching 

 from the second brood of eggs for the year, making two full broods 

 annually besides the partial broods. 



The winged examples that migrate to the blue spruce settle upon 

 the needles, secrete a large mass of cottony threads, deposit a patch 



