PUPATION. 335 



two experiments a very tine pin was run through the ore- 

 master, as near to the end as possible ; but it was found that 

 the pin injured the pupae, and consequently they died without 

 emerging. A very fine pin was run through the last seg- 

 ment of a pupa, which began to emerge, but died, being 

 unable to complete the process. In several other cases pupae 

 were stuck to the bottom of the box by means of a drop of 

 mucilage or a drop of sticky fly-paper gum. This was un- 

 satisfactory, however, for the pupae, in wriggling about, got 

 themselves covered with the gum, and the few which did 

 emerge were in very poor condition. 



Mass of PupcG. — When about to pupate, the caterpillars, 

 when numerous, collect in masses to spin their cocoons. On 

 the flat side of a rock one of these masses (Plate 49) was 

 found which measured eighteen inches in length and eight 

 inches in width, the whole being covered by one large net- 

 work of silk. Beneath two partly eaten leaves of oak forty- 

 nine caterpillars had pupated, and another mass was found 

 in a groove between the trunks of two small trees (Plate 

 47), containing at least three hundred pupae and pupa-cases. 



Pupation in the Field. 



To learn the proportion of caterpillars which pupate on 

 trees and on the ground, as well as the per cent, of those 

 parasitized, a study was made of the " Winning " colony at 

 Woburn, in the latter part of July, 1895, the results of 

 which show that the larger part of the caterpillars pupated 

 in the trees. On the border of the colony, about forty per 

 cent, pupated above the burlap ; while in the centre, about 

 sixty per cent, were found to have pupated above it. These 

 facts confirm the generall}^ accepted opinion that, when very 

 abundant, the per cent, of caterpillars pupating upon the 

 trees is somewhat increased. 



Of the caterpillars which pupated elsewhere in the col- 

 ony, the proportion was equally divided between those that 

 pupated on the ground and those which passed the pupal 

 stage on the trunks and under the burlaps on the trees. 

 All pupae which gave evidence of parasites, as well as the 

 empty pupa-cases from which parasites had apparently 

 emerged, were counted as parasitized. The per cent, of the 



