PARASITES HIBERNATING IN BROWN-TAIL WEBS. 291 



no 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 was something wrong which was 

 outside of the power of anyone at the laboratory to remedy, and it 

 was resolved to test the matter thoroughly in 1910. 



The caterpillar-dissection work which was begun in the spring of 

 1909 was carried on quite extensively in the winter of 1909-10, and 

 among the several lots of hibernating nests imported that winter those 

 which came from Italy and France were found to contain a very large 

 percentage of caterpillars bearing the larva? of Zygobothria (fig. 63, 

 p. 264). 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 trees which had previously been cleared of native 

 nests of the brown-tail moth with this end in view. 



The caterpillars, as usual, did remarkably well in both cases, and 

 as usual the three spring stages were 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- 

 gots 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. 

 Within 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. 



