310 EEPORT UPON COTTON INSECTS. 



seasons, and in dry sunshiny weather do least damage. The testimony 

 on this point is hardly as unanimous as with the cotton-worm, but it is 

 sufficiently so to enable us with justice to make the general statement. 

 As to the causes which produce this result, we can do no better than to 

 refer the reader to the discussion upon this point in chapter V of the 

 previous Part. Mr. Trelease says in this connection : 



Like the cotton-caterpillar, the boll-worm is more abundant in wet than in dry places ; 

 at least, such was my experience, and it is also said to do better in wet than in dry 

 seasons. This is readily explained by the hostility of ants, which are more abund- 

 ant in dry than in wet places, and in fair than in rainy seasons. 



Early in June several half-grown " bud- worms" were collected on Indian corn and 

 transferred to cotton-plants with a view to watching their actions. Care was taken 

 to place them upon plants on which there were no ants. Seating myself beside them, 

 I awaited developments. At first they evinced no desire to do more than conceal 

 themselves beneath the leaves from the glare of the sun. But it was not long before 

 a stray ant appeared on the plant, and, finding the larva, proceeded to run round and 

 round it, biting it whenever it could. 



Soon, however, finding that unaided it could do little, the ant left the plant, and, 

 after watching it a short time, I lost sight of it ; but in a few minutes it returned ac- 

 companied by several others of the same species. In a little while the worm was so 

 worried that it fell from the plant, and was soon killed and carried off by its tor- 

 mentors, which followed it to the ground. 



Several times I saw this repeated, the boll- worm being killed in each case within an 

 hour after the time when they were placed on the cotton. The black ant was also 

 seen to kill these larvae upon several occasions, and once or twice when the worms had 

 not been interfered with by me. 



Mr. Lyman, in Department of Agriculture report for 1866, says that 

 many eggs of the boll-worm moth are destroyed by ants. 



The theory of the ants influencing the comparative abundance of 

 worms in wet and dry weather is, as we have said before, an extremely 

 plausible one if its basis be correct. There cannot be the slightest 

 doubt but that ants abound upon dry soil rather than upon that which 

 is moist, and in dry, sunshiny weather rather than in rainy weather; nor 

 can there be the slightest doubt but that many species destroy both cotton 

 and boll worms. Then the theory will hold just so far as this destruction 

 goes just to the extent that the ants kill the worms. The fact that 

 there is a slight difference of opinion as to the influence of the weather 

 can then be easily explained by the comparative abundance of ants in 

 different localities. The theory does not, however, entirely account for 

 facts as observed, but will have to be taken in connection with the nectar- 

 gland theory, as put forth in Part I, and also with the facts of the su- 

 perior nourishing power of a tender and succulent plant, as compared 

 with one dry and dwarfed from drought. 



