Page:Popular Science Monthly Volume 37.djvu/347

Rh of the individual to choose what state he will serve. On the other hand, industrial co-operation, in its broadest sense, is becoming more and more compulsory; the distinction, therefore, between "voluntary" and "involuntary" "co-operation" is of ever-lessening importance. 

HE various insects which infest the dwelling have been from time immemorial a trial to careful housekeepers. Just as out of doors the gardener is constantly employed in protecting plants of all kinds from the ravages of insects, so in the house there is a perpetual warfare carried on against these indoor pests. Some eat holes in our clothes, others destroy carpets and hangings, while still others are attracted by the food in our pantries and storerooms.

Unless one has watched the habits of insects and studied their development, it is hard to realize that in their mode of growth they differ from the other animals with which we are familiar. By some it is supposed that an insect grows as a bird or a cat grows—that is, by imperceptible increase in size, with no marked change in form. With this idea it is not strange that a tiny fly should be thought a young fly that will gradually grow bigger, or that a large fly should be supposed to have lived some time to have attained such size. It is a fact fairly well understood that moths and butterflies pass through several changes between the egg and the perfect insect, and that the caterpillar, or worm, as it is more often called, seen feeding in our gardens, or crawling over sidewalks or fences in search of a convenient spot in which to undergo its transformations, will before long assume a totally different appearance; it is not so generally known, however, that in the larger number of insects the change is nearly if not quite as great.

Among the insects which infest our houses we find representatives of most of the various orders of insects, and a study of these forms alone would prove of interest and value. Their habits are well known to the housekeeper, and so in many cases is their appearance in one or more stages; but a history of their life from the egg to the perfect insect is still a mystery to many people, and it is to these that the following pages may be of interest. In this article attention is called only to the more common insect pests of the house.

(Tinea pellionella).—One of the commonest of 