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 Ist 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 larve 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 
