CONCLUSIONS UPON INFLUENCE OF WEATHER. 137 



is destructive to its natural enemies, the ant, and also an insect called 

 the ichneumon," &c. 



Professor Biley informs me in conversation that the same point has 

 been forced upon his attention during his investigations the past summer, 

 and it will probably be elaborated in the forthcoming bulletin of the 

 United States Entomological Commission. 



The following extracts from Mr. Trelease's note-book are of interest in 

 this connection : 



September 10, 1879. On the second place, where 100 acres are eaten out entirely, I find 

 thousands of nearly-grown aletias crawling in every direction. . In wet places they are 

 not so much molested by ants, for there are few of these; but on dry, sandy places I 

 find ants killing many 1 arvse. * * * Can it be that aletia first appears in wet 

 places because the ants are not so numerous there as on high, sandy places ? Early I 

 found caterpillars on both bottom and ridge land. Were not most of the latter killed ? 

 This theory must be taken in connection with that of the nectar, for certainly there 

 are more eggs laid in wet ground. Can it not be that this is partly due to the fact 

 that more moths are excluded in such places and lay their eggs without leaving them ? 



The one sentence, "Early I found caterpillars on loth bottom and ridge 

 lands," forms a strong argument for Mr. Davis's theory. 



And now as to our own conclusions : If it can be shown that the num- 

 ber of cotton- worms actually killed by the ants is as great as stated by 

 the upholders of the theory, then there can be no doubt but that it ac- 

 counts for observed facts. In the next chapter is given what evidence 

 we have collected as to the efficacy of the ants as destroyers of the cot- 

 ton-worm ; but it seems hardly sufficient to warrant us in unqualifiedly 

 supporting so broad a theory. We can safely say, though, that the agency 

 of the ants is one of the prominent factors in bringing about the dry- 

 weather scarcity or wet- weather abundance of the cotton-worm. The 

 most important time for the ants to be pursuing their good work is among 

 the early broods of worms in May and June. Every worm killed at 

 this time saves the cotton fr6m hundreds later. The numbers of indi- 

 viduals in the earlier broods are small, and more appreciable work can 

 then be done. Later in the season the abundance of the worms, if they 

 have been protected by wet weather earlier, is so marked that an ordi- 

 nary change of the weather has small influence over them. 



The law, then, which we should lay down for the influence of weather 

 upon the cotton-worm, taking all evidence into consideration, would be: 

 A mild winter, followed by a rainy May and June, will usually bring a 

 destructive "third crop" of the worms, while an opposite state of the 

 weather will be more likely to bring about comparative exemption. 



