54 INSECTS AND MAN 



of the full-grown larvae is their wide colour variation, even 

 when they have been reared under similar conditions ; some 

 are quite dark brown, others of a rose shade, and larvae of 

 yet a third type are green. 



We have mentioned that the young boll worms are 

 cannibalistic; but the habit is not confined to the early 

 larval stages, for when half grown, or rather older, they 

 are exceedingly vicious and are always ready to attack 

 one another. If the paths of two larvae, feeding in 

 proximity to one another, accidentally cross, they become 

 irritated and snap at one another. The larger one usually 

 kills and eats the smaller one, but if they are of approxi- 

 mately the same size, both may be mortally wounded. With 

 rare exceptions, whenever larvae meet accidentally on a food 

 plant they fight, though their antipathy to their fellows 

 does not go so far as to cause them to hunt one another 

 out with evil intent. " The boll worms appear to relish the 

 bodies of their unfortunate fellows, but soon sicken and 

 die if compelled to subsist for a long time on this sort 

 of food." 



When full grown, the larva leaves its food plant for the 

 soil, in order to pupate; when on the ground it at once 

 proceeds to work its way below the surface, pushing its 

 head against the soil, and, swinging it slightly from side 

 to side, it throws up a pile of loosened earth. The hole 

 (fig. 6) is about twice the diameter of the larva, though 

 it rapidly becomes filled with soil particles. The time 

 required to burrow beneath the surface depends largely on 

 the texture of the soil, and varies from five minutes to 

 nearly an hour. When buried, the larva still burrows, in 

 a slanting direction, to a depth of from one to seven inches, 

 then it turns upwards and forms a curved tunnel, with 

 smooth walls which it coats with silk. About an eighth 

 of an inch below the surface of the ground the tunnel stops 

 abruptly, and the larva, its burrowing operations completed, 

 pupates in the tunnel with its head towards the surface. 



