HABITS OF LAEVAE. 79 



ened, or sometimes when it wishes to move to another part of the plant, 

 it suddenly throws itself by a jerking motion into the air. I have care- 

 fully studied this mode of jumping. It is as follows : The larva clings 

 to its support by its three posterior pairs of prolegs; it swings the an- 

 terior part of its body to one side, and then, rapidly moving it to the other, 

 lets go at the proper moment; the momentum of the anterior part of the 

 body is sufficient to carry the whole body some distance. In this way a 

 larva can jump two feet in a horizontal direction. They will often spring 

 from the highest part of the cotton plant and fall to the ground. On 

 one occasion (August 26) I was in a field where the plants were nearly 

 stripped of their leaves at the top ; the larvae were moving to the lower 

 leaves. I saw none crawling down the stalks. All, so far as observed, 

 performed the journey by jumping. They rarely fail to alight upon their 

 feet and cling to the object touched. Not one in fifty strikes one leaf 

 and falls to another before getting hold with the hooks with which the 

 prole gs are furnished. Many, springing too far from the plant, would 

 touch no leaf and thus fall to the ground. This litrva does not seem 

 able to cling by its true legs, and, by swingingkhe posterior part of the 

 body, jump. When I press upon the head of the insect with a stick or 

 pencil, it seems unable to jump unless it can first withdraw its head. 

 But if the pencil be put on the posterior part of the larva, it will jerk the 

 anterior portion of the body so violently as to pull itself from beneath 

 the pencil. I have been unable to find any silk connecting the larva 

 with the object from which it springs ; and I am of the opinion that in 

 jumping it does not spin a thread. 



I did not observe a single instance of systematic marching, as is indi- 

 cated by the popular name army- worm, which has been so generally 

 applied to this species. I saw on several occasions immense numbers 

 of the larvae on the ground, crawling in all directions in search of food or 

 places in which to transform. And on one occasion (August 26) I saw 

 myriads of the worms of different sizes crawling in all directions over the 

 ground, when there was plenty of food and places in which to transform 

 on the plants, as not more than one-third of the foliage had been eaten. 

 This was the time when I observed so many larvae springing from the 

 stripped upper portions of the plant to the leaves below j perhaps most 

 of the worms on the ground were those which, in jumping, had failed 

 to alight on the lower leaves. I visited the field at night to ascertain if 

 the marching was kept up at that time. I found none crawling over 

 the ground, and nearly all those on the plants were perfectly at rest. 



When the larvae are feeding on the cotton in great numbers there 

 arises a peculiar sweetish odor, which, although not easy to describe, is 

 very characteristic. This odor, I supposed, proceeded from the excre- 

 ment of the Iarva3 ; but Mr. Trelease is of the opinion that it is " due 

 partially to the crushing of the leaves by so many mandibles." In any 

 case this odor is perceptible only when the larvae are present, in great 

 numbers. The fact that many planters say that they can smell the 



