CHERMES ABIETIS. 363 



silver fir, larch, or pines, and lay eggs from which wingless 

 lice arise that winter on the tree and lay eggs next spring. 



From these eggs some of the nymphs eventually become 

 winged lice that fly back to the spruce and lay eggs 

 there from which $ and ? arise. The other wingless 

 parthenogenetic ? continue their life on the other trees. 



1. Chermes abietis, L. (Spruce- gall Aphis), 

 a. Description. 



Wingless stem-mother, yellowish-green, becoming darker 

 when full-grown. Body covered with white wool. Gall- 

 dwellers bright yellow. 



Winged lice, 2 2'4 mm. long, with dark head and back and 

 yellow undersurface. Sexual insects bright yellow. 



b. Relations to the Forest. 



The galls (in size from that of a cherry to that of a walnut) 

 which result from their injury are at first soft and green, 

 becoming later purplish-red in places and finally, when hard 

 and dry, brown. They contain a quantity of tannin. Their 

 size is characteristic, as is the fact that they are topped 

 with a sprig of needles, as long as, or longer than, the gall. 

 This is the stunted young shoot. The injured shoots take on 

 a characteristic curvature towards the side on which the gall 

 is growing. The loss of growth may be considerable. 



The other hosts of this insect are larch, Scots pine, Cembran 

 pine, and in Eussia, the Siberian spruce. 



The spruce-gall aphis is common both in plains and in hilly 

 country, and attacks young spruces especially in nurseries and 

 those which have been injured by frost or animals. It is also 

 common on the border-trees of 10- to 20- year-old plantations. 

 Fortunately the attack is usually confined to the side-shoots, 

 and the leading shoot escapes. 



c. Remedial Measures. 



Protection of the smaller insectivorous birds : tits, the nut- 

 hatch and golden-crested wren. A spider (Theridion) is an 

 active destroyer of this insect, spinning its web over the galls 

 and preventing the escape of its inmates. Direct treatment is 



