The way in which the lives of all animals and plants are interwoven with that of other animals and plants, often in obscure and unsuspected ways, comes home to man when he contemplates the numbers and variety of living things which exist with him and upon him—that is to say, at his expense and to the detriment of the stores which he accumulates, the clothing with which he covers himself, and the buildings which he constructs. Man not only has carefully taken a number of animals and plants in hand and cultivated them as food-givers, as sources of clothing, and other useful material, but, much to his annoyance, he finds, per contra, that other animals (and plants, too), with similar self-seeking habit, make use of him in his turn, and of his belongings, with a complete disregard of his convenience, treating him and his arrangements as so much available “food-stuff,” and showing no atom of respect to him as the lord of creation. Just as in dealing with the more deadly attacks of disease-producing parasites, so in meeting the destructive invasions made by his fellow-creatures of all sizes and kinds in search of food and shelter—man has to be continually on the alert, and to wage a constant warfare, unless he will consent to see himself and his possessions moth-eaten, fly-blown, worm-burrowed, reduced to fragments and powder. And this warfare he has incessantly carried on with increasing skill and knowledge from the earliest times of which we have any record.

The sparrow and the rat, of which there has lately been much talk, are examples of fairly large, easily detected enemies of this kind. The almost ultra-microscopic bacteria—similar to those which produce disease by multiplying in the living body—are examples of the most minute living pests which injure man by causing sourness, putrefaction, and destructive rot in his food and stores. Every year civilised man is gaining greater knowledge of these “ferment organisms,” and vastly increased skill in preserving his possessions, such as food and drink, from the attacks of their ubiquitous swarms. Between the larger depredators, such as birds and rats, and the smallest, such as the microscopic bacteria and moulds (to whom alone putrefaction is due, and without whom it would never occur), there are a host of small troublesome creatures, which belong chiefly to the group of animals called “insects”—beetles, moths, flies, and bugs—which give man incessant occupation in warding off their attacks upon his food, his clothes, his furniture, his buildings, his crops and fruit trees, and his domesticated animals. The study of these things and of the means of grappling with them is the fascinating occupation of those who are called “economic” zoologists and botanists. Of course, in order to carry on their inquiries successfully they have to bring to bear on the questions they investigate as complete and thorough a knowledge as possible of all the kinds of animals and plants, and of their ways of feeding, reproducing, and protecting themselves in natural conditions.

One of the most widely celebrated and anciently detested of insect pests is the clothes moth. It is the caterpillar of this moth which is objectionable—biting off, eating, and using to weave a case the hair of furs and the fine filaments of woollen fabrics. Not every one is able to recognise the clothes moth, which is a very small creature of a greyish-yellow colour. The wings when set for flying measure only half an inch in expanse, and when the moth is walking or at rest, shut closely to the body so as to give it an almost cylindrical shape, with an attenuated snout. Much bigger moths occasionally get into our rooms, but do no harm. These little clothes moths lay their eggs on fur or wool, and the caterpillars which hatch from them do the damage. The moths themselves have no jaws and take no food. But the caterpillar or grub, though soft and readily crushed, has a pair of very hard, minute, dark-coloured jaws, with which it works away, cropping the fur and wool on which it lives. The moths are seen in houses commonly between January and October, and it is, of course, the object of the victimised householder to destroy them before they can lay eggs, or, what is more practical, to keep woollen and fur clothes away from their reach. Things which are in daily use are not very liable to receive a deposit of eggs from the clothes moth, and as a rule the enemy may be kept at bay by daily shaking and beating the things in question, and hanging them up in the air. But coats, flannels, etc., which are hidden away, left quietly in drawers or cupboards, offer the undisturbed conditions which the clothes moth seeks. There is no safety for them unless they are wrapped up or shut in with a quantity of naphtol or of camphor, or, as is nowadays more usual, placed in a refrigerating chamber.

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.

An interesting fact about the movable case made by the clothes moth caterpillar is that the nearest thing in nature to it is the case made by the aquatic grubs or caterpillars of another kind of insects—the caddis-worms (“case-worms”) which are common in ponds and streams. They show extraordinary powers in making their cases so that they balance nicely in the water, as the animal crawls along on the bottom of a pool, with his head and six legs emerging from one end of the case. Caddis-worms are of various kinds or species, and some attach to their cases little broken sticks, others minute empty snail-shells, others the fine green threads of water-plants. The caddis-worm becomes changed into a delicate fly, with transparent wings, just as the clothes-grub becomes changed into a moth—and it is an interesting fact that the caddis-flies, though they are classed with the May-flies and such net-winged insects, and not with the moths and butterflies (the Lepidoptera, or insects with wings covered with dust-like scales, which give the colour and patterns to the wings), yet agree with moths in having some scales on the wings and with one kind of minute moth, namely, the clothes moth, in having grubs which make movable cases.

The clothes moth caterpillar was known to the Romans by the name Tinea, and is described with correct detail by the Roman naturalist Pliny. Modern naturalists have accepted this name Tinea as that of the genus to which the clothes moth belongs. There are thirty different British species of Tinea, of which four are guilty of attacking animal fabric, and so causing trouble to man. The one which builds a case and is the titular chief of the clan of clothes moths—“the” clothes moth, just as one may say “the” Macintosh—is scientifically indicated by the name Tinea pellionella. The other three do not form movable cases when in the caterpillar stage, and attack coarser stuff than fur and fine wool. One of them is known as the “tapestry moth,” because its caterpillar establishes itself in old tapestry and carpets, and burrowing into these thickish materials is concealed without the aid of any self-provided tunic or case. The name Tinea is often used by entomologists in an expanded form as Tineina, to indicate the whole series of minute moths of which the genus Tinea is only one little group. Many of these moths are much smaller even than the clothes moth, and they are found in all parts of the world and in all sorts and conditions of life—in relation to trees, shrubs, and plants of all kinds. It has been estimated that there are as many as 200,000 distinctly marked different kinds of these minute creatures. The insect collectors and students who occupy themselves with the magnificent butterflies and larger moths (of which there are an enormous variety of kinds) refuse to deal with the somewhat dull-looking and almost innumerable minute moths which are classed as Micro-lepidoptera, in contrast to the Macro-lepidoptera (or big moths and butterflies). Consequently they have become the favourite study of a few enthusiasts, who are known as Micro-lepidopterists, and have a wide but not uninteresting field of exploration all to themselves. The Micro-lepidoptera include, besides the Tineina, a group of less minute though small moths, with narrow, fringed wings, amongst which are the window moth, the milk moth, the tabby moth, the meal moth, and the grease moth. Though the clothes moths may well be described as “tiny” moths, yet the word Tinea, as applied to them, has no such origin, but is the name given to the destructive grub by the Romans. The same word has unfortunately been applied by medical men and botanists to a vegetable parasite which causes a skin disease (ringworm) resulting in baldness. The Tinea calvans of the doctors has only this in common with the moth Tinea pellionella—that it causes hair to disappear and baldness to ensue; but the vegetable parasite attacks the hair on a living man’s head, the caterpillar that on his fur coat.