PARASITES HIBERNATING IN BROWN-TAIL WEBS. 291 
do particular difficulty had been experienced in feeding small numbers 
of the caterpillars from native nests through all of their spring stages. 
As was the case in 1907, the caterpillars passed through the first 
three spring stages with scarcely any mortality, and, as before, trouble 
was finally encountered. In the first place a considerable propor- 
tion of the trays was infected with the fungous disease, which had 
been accidentally brought in from the field, and these had to be 
destroyed summarily. There were still a number of the trays unaf- 
fected, however, and these were given the very best care which pre- 
vious success with native caterpillars and failure with imported cater- 
pillars suggested. In spite of all the results were exactly as before, 
and, as before, only an insignificant number of the Zygobothria com- 
pleted their transformations. It was all the more surprising because 
there were several of the smaller and choicer lots which were kept in 
a cool, airy place, side by side with trays of native caterpillars, fed 
upon the same food and given identically the same attention, and 
yet every single individual of the one lot died, while nearly every 
individual of the others went through to maturity. 
It began to look as though there wa> something wrong which was 
outside of the power of anyone at the laboratory l«> remedy, and it 
was resolved to test the matter thoroughly in 1910. 
The caterpillar-dissection work which was begun in the spring of 
190!) was carried <»n quite extensively in the winter of 1909-10, and 
among the several lots of hibernal ing Qfists imported that winter those 
which came from Italy and France were found to contain a very large 
percentage of caterpillars hearing the larva 1 of Zygobothria (fig. 63, 
p. 204). These caterpillars, as soon as they emerged from these nests 
in the spring, were separated into two lots. A part of them was fed 
in trays, as before, and another part was immediately placed in the 
open, upon small oak t rees w hich had previously been cleared of native 
nests of the brown-tail moth with this cud in view. 
The caterpillars, as usual, did remarkably well in both cases, and 
as usual the three spring stages wore passed in the normal manner. 
At the end of that time those which had been fed in trays began to 
die, and those in the open to disappear. Mr. Timberlake, who was 
assiduously trying to follow the development of the Zygobothria mag- 
got-, throughout their later stages, found it increasingly difficult to 
find the caterpillars in very large numbers in the field where they had 
been colonized, and finally of the thousands originally present only 
about 150 could be found. These had reached their last stage by this 
time, and they were collected and brought into the laboratory. 
AY it bin a few days all but a very small number had died, and as there 
was a good chance that a few native caterpillars were present, there 
was nothing to indicate that all of the survivors were not native 
instead of imported. 
