2GG REPORT OP THE COMMISSIONER OF AGRICULTURE. 



of the leaf according as they happen to be on one side or the other, but 

 do not perforate the h^af till two to four days old. Tbe Idjiuv done to 

 the cotton during this early part of the life of the larvae if> inconbidcrable. 



Obeervations made in the held during the month of xVugust indicate 

 that, as a rule, this insect lives at that season thirteen days as a larva, 

 before webbiug up, and remains as a larva oue day after this, before 

 changing to a pupa. Occasionally two days elapse between the web- 

 bing up and the change to pupa. Specimens which were kei)t in breed- 

 ing-cages in my office" remained eighteen days in the larval state. This 

 unusually long time was probably due to the fact that the temperature 

 of the room in which they were kept was much lower than that in the 

 cotton-fields. Specimens bred by Professor Glover under similar circum- 

 etances passed twenty days before webbing up.* 



The larva sheds its skin five times during the period of its growth. 

 The individuals v;hieh I bred molted at regular intel^'als of three days, 

 the first molt being made when the larvae were three days old. At 

 this molt nearly all the larvae ate their shed skins. During the first 

 stage the hetul of the larva is marked only by the six black eyes on either 

 side. After the first molt the conspicuous black spots on the head 

 appear. When six days old the larvae molted the second time, and 

 when nine days old the third molt occurred. At this molt the larvae 

 began to vary in color; some becoming striped with black and others 

 remaining green. On the twelfth day the fourth molt occurred, and 

 the fifth molt on the fifteenth day. Three days later the larvae webbed 

 up. When full grown the larva measures one and five-eighths inches 

 in length. A detailed deseription of the full-grown larva is appended 

 to this section. 



The variation in color referred to above is quite interesting ; no expla- 

 nation of it has been discovered. I found by experiment that the dis- 

 tinction is not a sexual one, as moths of each sex were bred from each 

 kind of larvae. General observations, that is, those made without abso- 

 lutely counting the individuals of each color, show that there are no 

 dark larvae in either the first or second broods. About one-fourth, or 

 less, of the third brood are striped with black. About one-half, or 

 slightly ^lore, of the fourth brood are dark, many of them being almost 

 entirely black ; while nearly all of the fifth brood, " third crop" of the 

 planters, are black or very darkly striped. 



After the larvae become large enough to eat through the leaves, or, in 

 the language of the planter, " to rag the cotton," they move to the top of 

 the plant and destroy the tender terminal foliage ; thus the earliest indi- 

 cation usually obser\^cd of the presence of the worms is the " ragging" 

 of the tops of the plants. As already stated, this has led to the practice 

 of '^topping" the cotton. 



In feeding, the worms rest upon either the upper or lower surface of 

 the leaf, but more frequently upon the latter. They eat most early in 

 the morning and latxj in the evening. As we have frequently observed 

 with other caterpillars, the cotton-worm may often be seen resting upon 

 some portion of the plant, supporting itself by its prolegs and swinging 

 the anterior part of its body from side to side as if fanning itself. The 

 larva has another interesting habit. When touched or otherwise fright- 

 ened, or sometimes v/hen 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 ciingg 

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



' Agricultural Report, 1855, p. 75. 



