PARASITES HIBERNATING IN BROWN-TAIL WEBS. 293 



from the nests had they not been exposed to undue warmth during 

 the winter. 



It makes little difference whether the nests are exposed to one 

 temperature or another during the winter so long as the caterpillars 

 are not actually stirred into activity; the date of final emergence in 

 the spring remains practically unchanged. Roughly speaking, if 

 brown-tail nests are exposed to a constant high temperature begin- 

 ning at any time during October the caterpillars will die without 

 becoming active; during November they will die if kept too warm, 

 but become active in a little over a month if kept warm and humid; 

 in December they will sometimes become active by the 1st of January 

 if they are kept fairly humid, and during January they will nearly 

 always become active in a little less than a month, no matter what 

 the conditions of humidity; after the 1st of February activity is 

 resumed in something like two weeks; after the 1st of March in about 

 one week, and later in a few days. If kept at a high temperature 

 for three weeks in December or two weeks in January and then placed 

 under natural conditions for the rest of the winter, their emergence 

 will not be appreciably hastened in the spring, but if the attempts to 

 rear Zygobothria from imported caterpillars which have been handled 

 in much this manner are to be properly interpreted, subjection to 

 such abnormal conditions results in a subtle disarrangement of the 

 vital processes, and the insect is metabolistically unbalanced. 



It is hardly necessary (to return to the story of Zygobothria) to 

 state that these successions of almost total failures were not only 

 puzzling, but decidedly exasperating. In 1910, for example, we 

 estimated the number of apparently healthy Zygobothria larvae on 

 hand in apparently equally healthy caterpillars to be something like 

 40,000, of which something like 10,000 or 15,000 were in the cater- 

 pillars which were feeding and growing in a perfectly natural manner 

 in the open. Long before it was time for these caterpillars to pupate 

 we had given up all hope of more than an insignificant number of 

 these parasites going through to maturity, and, as a matter of fact, 

 there is no record of a single one among them going through. Every 

 resource had been exhausted the winter before in attempting to 

 secure a shipment of nests of the brown-tail moth in good condition 

 from some locality where there was a likelihood of Zygobothria 

 occurring in abundance as a parasite, and the failure was even more 

 complete than usual. There remained only the alternative of import- 

 ing large numbers of full-fed and pupating caterpillars of the brown- 

 tail moth, collected in the same localities, and the prospect that this 

 would be successfully accomplished was far from brilliant. The 

 senior author was in Europe at the time when these conclusions were 

 formed and was putting forth his utmost endeavors to bring about 

 this very thing, but June passed, and with the advent of July it 



