THE LEPIDOPTERA 233 



The internal structures of the caterpillar do not differ greatly in their 

 arrangement from those of an adult insect, except that the reproductive 

 organs are only slightly developed at this time, and in the presence 

 along each side of the body of a silk gland, large in those which will 

 later need large quantities of silk, but present in all. A duct from each 

 gland runs forward to the mouth where the two unite and open to the 

 exterior through the spinneret already referred to. 



Most caterpillars feed on plants or vegetable material. Their work 

 is noticed chiefly by their stripping plants of their leaves, though some 

 bore in stems, roots, fruit, seeds or other parts. A few attack feathers, 

 silk, etc.; but this is not the general habit. The larval stage may last 

 only a few days for some species but is generally a month or more, and 

 some feed during the fall, become quiet during the winter, and complete 

 their feeding the following spring. 



A large majority of the caterpillars are termed naked, having only 

 a few tiny spines or hairs, not large enough to be noticeable. From 

 this condition every grade of density of covering occurs, to species entirely 

 covered by long, thickly placed hairs which give the animal a hairy or 

 " woolly " appearance. Some have large warts or horns on the thorax or a 

 sort of horn above, near the hinder end of the body. 



Their colors also vary greatly, some being brightly colored while 

 others, green, either with or without white streaks, appear to seek con- 

 cealment by their resemblance to the leaves on which they feed. Those 

 living in protected situations, such as in plant stalks, are nearly white: 

 cutworms which pass the day in the ground are dark as a rule, with 

 rather faint markings. 



When the caterpillar has become full-grown it generally leaves the 

 place where it was feeding and in some satisfactory location, spins a 

 cocoon around itself, using for this purpose the silk produced by its 

 silk glands. In some species the cocoon is very complete, thick, tough, 

 and entirely conceals the larva within. On the other hand, there are 

 cocoons where only sufficient silk is used to attach the insect and hold it 

 in place ; and between these extremes all degrees of cocoon construction 

 occur. Sometimes leaves, hairs from the body of the caterpillar, or dirt 

 when the insect enters the ground at this stage, are incorporated in the 

 cocoon. 



Within the cocoon the caterpillar molts, leaving its cast-off skin at 

 one end. The result of this molt is a pupa, its form showing through 

 its new skin which is generally brown, the outlines of the adult body 

 and its appendages including the wings being evident, these last, however, 

 very small as there would be no room for the full-sized wings of the adult 

 within the cocoon. Internal changes and the completion of such external 

 ones as are necessary, now proceed until the adult insect has been entirely 

 formed, and is ready to escape. When this happens another molt re- 



