The little caterpillar which does all the damage is of a dull white colour, with a reddish head. It is remarkable for the fact that it makes a sort of movable tunic or case for itself out of the hair or wool which it crops, and it crawls about protected by this case. There are not many insects which thus construct portable cases for themselves when in the grub or caterpillar state of life. Such “cases” must not be confused with the very similar “cocoons” by which some moth-grubs surround themselves (as, for instance, the silkworm moth) when their growth is completed, and they become quiescent and hard, and are known as chrysalids. Such “cocoons” are constructed in the same way as the lining of the clothes moth’s case, by threads of silk secreted by the caterpillar, but they are made once for all when the grub has ceased activity. The little clothes moth caterpillar, on the other hand, has continually to enlarge its tunic or case as it itself increases in size. There is a hole at the end, from which the head and three legs of the caterpillar emerge, so that it can crawl and feed freely. The outer surface of the case consists of cut lengths of the fibre on which the grub is living, and so is protective in resembling the surrounding material and hiding the minute ravager. It is easy enough for the little grub to add a bit to the case at the end from which its head protrudes, and, being very flexible, it can turn right round in the tube and put its head out at the other end and secrete a bit more there, cementing cut hairs to the outer surface. But in order to increase the breadth of the tube or case, the caterpillar has, from time to time, to undertake a formidable operation. It actually slits up the case lengthwise for about half its extent, and fills in the gaping space with new material; then it cuts up the opposite face of the same half of the tube, and puts in a new patch there. And after that, it has to treat the remaining half of the tube in the same way, making two more cuts, one opposite the other, and filling in the gap in each case as before. Students of these little creatures have amused themselves by changing the position of the caterpillar and its case, from fur or wool of one colour to fur or wool of another colour, and in this way the industrious caterpillar is made to work in different coloured fibre in successive enlargements of his case, so that it becomes a Joseph’s coat of many colours.