62 PROTECTION OF PLANTS, 1917-18 



head and the upper part of the first thoracic segment are bright coral red. Two 

 long black pencils of plumed hairs project from the sides of the first thoracic 

 segment over the head, and a similar pencil upwards and backwards from the 

 median line of the eighth abdominal segment, the twelfth including the head. 

 The body is sparsely clothed with long, greyish hairs arising in radiating tufts 

 from yellowish tubercles. 



The rusty tussock 'caterpillar differs in being less brightly coloured and 

 in having a pencil of long black hairs on each side of the fourth segment behind 

 the head. 



The Pupa. — The adult caterpillars spin greyish silken cocoons attached 

 usually to the bark of tree trunks. Within the cocoon the caterpillar changes 

 its skin and appears as the chrysalis. The male chrysalis is brown or nearly 

 black, and sparsely clothed with greyish hairs; that of the female is much larger, 

 without the distinct wing cases, and has a transverse patch of light-coloured 

 scales across the back of each of the first three segments behind the head. The 

 cocoon of the female is tougher and darker in colour than that of the male. 



The Life-History and Habits. 



The winter is passed in the egg-stage in the white conspicuous egg-masses, 

 attached usually to the cocoons. Normally the egg-masses are deposited upon 

 the trunk and the under side of the larger branches, but in seasons of great 

 abundance they occur in considerable numbers in the upper parts of the trees 

 and upon nearby objects, such as fences and buildings. 



The eggs hatch usually during the month of June. In very early seasons 

 in the district about Montreal, some egg-masses hatch in the last week of May, 

 and the greatest activity in hatching is in the first half of June; in late seasons 

 the greatest activity in hatching is in the last half of June, and many egg-masses 

 remain unhatched until early in July. The species, therefore, remains in the egg- 

 stage for practically ten months, from about the end of July until the following 

 June, and a long period is offered for control by the removal of the egg-masses. 



The young caterpillars spread somewhat over the foliage, and feed individu- 

 ally on the under surface of the leaves, dropping by means of a thread of silk 

 when disturbed. As they increase in size the wandering habit becomes more 

 marked, and they devour the greater part of the leaf, seriously or completely 

 defoliating the trees when their numbers are great. They complete their growth 

 in from four to six weeks. Many of the large caterpillars wander about freely 

 from tree to tree, so that trees which have been pre^'iously clean may become 

 very badly invested by them. The older caterpillars are thus distributed locally 



