362 ENTOMOLOGY 



Many examples of adaptation in relation to winter conditions will 

 suggest themselves. Insects when about to hibernate seek shelter or 

 construct shelter, or both. They may simply crawl into existing 

 crevices or holes, as in the ground or in plants, under stones, logs, loose 

 bark, dead leaves, among stems or roots of plants, or may burrow into 

 the ground or into living or dead plants; or may make cocoons or silken 

 nests or earthen cells, in which protection is afforded by surrounding air- 

 spaces. A curious situation for hibernation is that of back-swimmers 

 (Notonecta) , which have been found clustered in small cavities in thick 

 ice. Hibernating insects protect themselves more or less successfully 

 from such adverse influences as sudden changes of temperature, excess 

 of moisture or of dryness, invasion by fungi and bacteria, and from 

 attacks by other insects or by birds or mammals. 



There are, however, many examples of unsuccessful hibernation. 

 Exceptionally low temperatures occasionally exterminate the boll weevil 

 in certain areas, the mortality being increased by excessive rainfall. 

 Concerning the caterpillars of the brown-tail moth in their winter nests, 

 Sanderson says that where nests of average size containing 300-400 

 larvae were subjected to 24 F. or lower, from 72 to 100 per cent, of 

 the larvae were killed, but that in large nests from the same locality only 

 57 per cent, were killed; the larvae in the outer parts of the nests dying 

 first. 



Following a period of subnormal temperatures in the state of 

 Washington, 1919, examinations were made of larvae of the codling moth 

 under bark or burlap bands. It was found that wherever the minimum 

 temperature had been lower than 25 F. all larvae were killed. On 

 higher ground, where the minimum temperatures ranged from 20 to 

 25, 80 to 90 per cent, of the larvae were killed. On still higher 

 ground, with minimum temperatures of 15 to 20, the mortality 

 was approximately 70 per cent. One interesting fact noted was that 

 frequently, on tearing away the burlap band, one or two living larvae 

 would be found in the midst of a number of dead ones. It seems impos- 

 sible, in these cases, that the living larvae had any more protection than 

 the others. They must simply have had more vitality. (E. J. New- 

 comer.) 



Distribution. Minimum temperatures exert an important influence 

 in limiting the northern distribution of insects, according to Sanderson, 

 from whose article on the subject the following extracts have been taken. 

 In New Hampshire (January, 1907) most of the hibernating caterpillars 

 of the brown-tail moth (excepting those in large nests) were killed off by 



