A Plum Scale, 691 



able to follow the life-histoty of the pest closely. The little 

 scales moved about but little, if any, during the summer ; and 

 also grew exceedingly slow as compared with the surprisingly 

 rapid growth of their mothers in the spring. In a month the 

 little creatures had gained scarcely -i mm. (.004 of an inch) in 

 length, and yet they had already caused many of the leaves to 

 curl, the fruit began to show their effects, and the trees presented 

 a smutty disgusting appearance. The amount of honey dew 

 secreted by each individual scale was doubtless very small during 

 the two months (July and August) that they worked on the 

 leaves. But the aggregate from millions of the little scales was 

 sufficient to completely coat the trees, including their leaves and 

 fruit. The pest did more damage this year while in this young 

 stage on the leaves than at any other period of its life. 



Fall migration. — August 21, Mr. Hooker wrote us that some of 

 the scales "were on the march." It was found that they were 

 moving to the undersides of the branches where there were still 

 many of the old shells of their mothers from which the little 

 scales had emerged more than two months before. This migra- 

 tion continued until most of the leaves had fallen ; probably a 

 majority of the scales had established themselves on the branches 

 by October i. Most of them sought the undersides of the smaller 

 branches, and in many instances they were to be found in these 

 places in such numbers as to form two or three layers of scales on 

 the bark. Thousands of them, however, crawled into any shelter- 

 ing crevice on large or small limbs or even on the trunk of the 

 tree. Figure 4 shows how thickly they congregated on the under- 

 side of a small piece of board placed under a rope to protect the 

 bark ; the large spiny objects on the board are the pupae of a 

 Lady-bird beetle, one of the enemies of this scale described farther 

 on. 



In August, the scales became light brown in color,and this deep- 

 ened into a dark seal brown when the migration began. 



Some of the scales did not migrate to the branches this fall. 

 From material sent us by Mr. Hooker, we estimate that about 10 

 per cent, of them fell to the ground with the leaves. Many of 

 these will doubtless find their way to the trees again in the spring. 



Hibernation. — When the scales migrated from the leaves to the 



