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.
XXXVIII
STONE AND WOOD BORERS
Boring into wood is a favourite proceeding on the part of many small
creatures, insects, shrimps, and ship-worms, by which they not only
acquire nourishment, but at the same time penetrate more and more deeply
into safe quarters and concealment. It is not surprising that it has
become the necessary and regular mode of life of a host of small
animals, and consequently that man who wants wood in good sound blocks
and planks for his various constructions is a good deal put out by the
voracity of the wood-boring community. To some extent he has given up
the task of checking their proceedings, and now uses metal where he
formerly used wood, but that only applies to a limited field. Wood is
still the great material of rough construction, and the main substance
used in fittings and furniture.
In our own country and in most parts of the world there are large grubs
or caterpillars, such as those of the goat moth, three inches long and
as thick as one’s finger, which eat into the stems of trees and spoil
the timber. The grub of the handsome moth known as the wood leopard is
another of these. It attacks poplar trees, and we used to take it in
numbers in the London parks and squares when I was a collector. The goat
moth is specially destructive to willow trees. But there are a very
large series of smaller grubs and adult insects which injure trees or
bore or devour wood already cut and dried. Among these are the saw-flies
and a number of beetles, and in Sicily and the tropics there are the
wonderful white ants which are not ants at all, but more like May-flies.
The destruction caused by these borers and eaters of wood is increased
by the fact that when they have riddled a piece of wood, moisture
penetrates it, and vegetable “moulds” flourish within it and complete
the break-up. Among the most destructive borers of wood are those which
attack the ships and piers of wood placed by man in the sea. These are
certain shell-fish, called ship-worms (_Teredo_), which are really
peculiarly modified mussels. There is also a tiny shrimp-like creature,
the _Limnoria terebrans_, which does enormous damage by its borings to
piers of wood erected in the sea. True insects do not flourish in the
sea. There are marine bivalve shell-fish which bore into clay,
sandstone, chalk, and even into hard granite-like rock. They do not use
jaws or teeth for this purpose, but the surface of their shells, which
are sharp and spiny, and also the sand which adheres to their soft
muscular bodies like emery powder to the pewter-plate of a lapidary’s
wheel. You may see the large and small holes made by _Pholas_ (called
also “the piddock”) and other bivalve shell-fish in the clay and chalk
rocks of the seashore on most parts of the English coast.
Most boring animals swallow the material which they excavate in the act
of boring, just as the earth-worm swallows the soil into which it bores,
and as many sand-worms do, throwing out from the hind end of the body,
in the form of a little coiled-up heap, a vast quantity of undigested
matter which has passed through them. But many insects which swallow
some of the material disengaged by their jaws remove, in addition, a
large quantity which is ejected from the boring as powder, like
sawdust, and others do not swallow any of the material into which they
bore. So, too, the _Pholas_ and marine-boring mussels do not swallow the
material which they loosen. It is a very slow process, the boring in
rock, and the fine particles rubbed away by incessant movement are
carried off in the sea-water.
To some extent the marine creatures which bore in rocks seem to be
helped by chemical action, since they show a preference for chalk and
limestone, easily dissolved by weak acid secreted by the borer, though,
clearly enough, they are not dependent on such chemical aid since we
find them also boring in insoluble granite rock and shale and clay.
There is one true worm-borer which perforates hard limestone pebbles and
chalk rocks, so as to give them the appearance which we call
“worm-eaten” when caused by another sort of worm and observed in a very
different material, namely, old furniture and woodwork. At Tenby, in
South Wales, the limestone pebbles on the beach are quite commonly
riddled with these worm-holes, truly “worm-eaten.” When they are not too
abundant one can see that the holes are arranged in pairs like a figure
8, about half the size here printed. On splitting the rock or stone one
finds a deeply-running U-shaped double tube excavated in the stone. In
this the little worm lived. It is easiest to get at the worms in a fresh
and living state on a coast where there are chalk-rocks and sea-washed
lumps of chalk. The chalk is easy to split and cut at low tide, and then
the little key-hole apertures can be broken across and the soft red worm
extracted. It is a beautiful red-blooded little worm—little more than
half an inch long—with two tactile horns on its head and little
bristles and gills on the rings of its annulated body. It is a true
“worm,” like the earth-worm, what naturalists call by the not
displeasing name an “annelid.” It seems at first sight impossible that
this delicate little thing should “worm-eat” the hardest limestone. It
has no jaws, but one of the rings or segments of the front part of the
body has two of its bristles swollen to relatively gigantic size, hard
and black. These are its boring organs, but I have no doubt that it is
helped, especially in its young state when commencing to bore, by an
acid secretion from the surface of the body.
Curiously enough, in the strict sense of the word “worm,” the boring of
chalk and stones by the little marine creature just mentioned (whose
name is _Polydora_) is the only instance of a “worm-eaten” condition
being produced by a real worm. The worm-eaten condition of wood is
produced either by the grub of a minute beetle (which is not in the
strict sense a “worm”) or by an ingenious human maker of “antiques” who
imitates the little holes on the surface of the woodwork of old
furniture, so as to pass off clever reproductions for really ancient
cabinet work. The little holes to imitate those of the true insect
furniture-borer are sometimes produced by discharging a gun loaded with
fine shot at the piece of furniture which is to be passed off as
ancient. But knowing purchasers probe the holes so made with a carpet
needle, and discover the lead-shot sunk in the wood. Hence there has
arisen a profession of specially-skilled “worm-eaters,” who, by careful
boring, imitate the holes made by insect grubs.
And now we come at last to the actual, real furniture worm or grub. It
is the grub of a small beetle—the _Anobium domesticum_, scarcely
one-fifth of an inch long (Fig. 62_c_), greyish-brown in colour, of a
cylindrical shape, with the head completely concealed or overhung by the
next division of the body, the thorax. The grubs are longer, soft, pale,
and fleshy. The sign of the presence of the _Anobium_ in your furniture
is the existence of small circular holes here and there on the surface
of the wood, with occasionally a little heap of yellow dust on the
ground beneath them. This last sign is in fact the only proof you can
have that the holes are not ancient and the burrows deserted, and that
the enemy is still alive and at work. Rarely, if ever, can you see
either the grub or the completed beetle into which it changes after
forming a cocoon within the burrows, for they very seldom leave their
excavations. But if you break up the wood you will find a surprising
number of long, cylindrical passages, running side by side, and for many
inches, through the deeper part of the wood, so that it may be quite
rotten and ready to crumble, although presenting an uninjured surface
save for the little round holes here and there. In these passages you
will find both the grubs and the adult beetles.
[Illustration: FIG. 62.—_a_, the death-watch beetle (_Xestobium
tessellatum_) of the natural size (one-third of an inch long); _b_, the
same beetle enlarged; _c_, the beetle (_Anobium domesticum_) whose grub
is the furniture-worm, of the natural size, a side view.]
A closely-allied and somewhat smaller species of _Anobium_ common in
houses is of a more voracious character, not confining itself to dry
wood, but eating bread, biscuits, rhubarb, ginger, and even cayenne
pepper. This second kind, called _Anobium paniceum_, is the real
“book-worm”; it gets into old libraries, and the grubs bore their
cylindrical tunnels from cover to cover of the undisturbed volumes. In a
public library twenty-seven folio volumes standing side by side were
perforated in a straight line by one individual _Anobium_ grub or
book-worm, and so regular was the tunnel thus eaten out that a string
could be passed through the whole length of it, and the entire set of
twenty-seven volumes lifted up at once by it.
There are one or two other grubs which less commonly injure books, and
pass as “book-worms.” But the most notable of the insect enemies of
books and papers is a curious little wingless insect which never passes
through a grub stage of existence, but hatches out in the complete form
of his parents. He is about a third of an inch long, has the shape of an
elongated kite, with a long tail and six legs, and is called by old
writers “the silver-fish,” and by entomologists _Lepisma_ (Fig. 63).
This little pest does not burrow, but nibbles, and has destroyed many a
valuable old document and ancient book. Paste and sugar are a great
attraction to him, and he will destroy a boxful of printed labels or a
valuable manuscript, leaving only the ink-marked parts untouched, but
ready to crumble.
Closely allied to the book-worm beetle, _Anobium_, is a larger beetle,
called _Xestobium tessellatum_ (Fig. 62 _a_) which infests old woodwork,
its grubs making correspondingly larger tunnels. The entire woodwork of
a house has had to be removed and replaced in consequence of this
creature’s depredation, and such pieces of furniture as a four-post
bedstead have been riddled and made rotten in two or three years by its
burrowing. It is still common in England in old wood-panelled rooms and
in wooden mantelpieces. The most interesting fact about it is that it is
the maker of those nocturnal tappings which are known as the
“death-watch.” It is the beetle itself (Fig. 62 _a_), not the grub,
which makes these sounds. It makes them by deliberately striking the
wood on which it stands, with its head. The taps are usually from five
to seven in quick succession, the sound dying away in intensity in the
later strokes. A second, and even a third, beetle will then reply with
similar taps from the woodwork of some other part of the room. Years
ago I used to be gently lulled to sleep by these “raps” in my rooms at
Oxford, accompanied by the sound of spasmodic rushes of mice behind the
woodwork. At first I thought the tapping was caused by the falling of
drops of water through a leaky roof, but soon ascertained the actual
cause. One does not notice these tappings until the dead of night when
all else is still, and they are so mysterious and persistent that one
can understand superstition arising in connection with them, and that
the nerves of any one already overwrought, might be so affected by them
as to lead to the belief that evil spirits are “rapping,” or that a
ghostly coffin is being nailed together for a dying man. The little
beetle has often been tracked by a naturalist, and discovered in some
concealed position nodding its diminutive but hard head with sharp
jerks, and producing an almost incredible volume of sound in proportion
to its size. If the beetle, when discovered, is kept in captivity in a
wooden box, it is easy to set it “tapping” or “rapping” by tapping
oneself with a pencil on the table on which the box is placed, when the
faithful little death-watch will unfailingly reply. Possibly some of the
“raps” recorded by the pioneers of spirit-rapping, when not produced by
the toes of designing mediums like the young ladies of Rochester, N.Y.,
were actually made by death-watch beetles. It is certain that the
somewhat eccentric supposition that disembodied spirits endeavour to
make signals to living humanity by “rapping” owes its origin (long
before the nineteenth-century craze for “spirit-rapping”) to the
measured tap-tap-tapping of the death-watch beetle, and the consequent
superstition at a time when the beetle was not known to be the “tapper.”
Whilst the bigger beetle, _Xestobium_, is the common death-watch, it has
been proved that the little furniture beetle, _Anobium_, is also a
tapper, making regular and persistent strokes like the ticking of a
watch. Another insect, called the book-louse (_Atropos divinatoria_),
very minute, only one-twentieth of an inch, soft, white, and wingless,
not a beetle at all, but also a devourer of literature (Fig. 64), is
declared by some good observers to be a “ticker” or “tapper,” but other
naturalists deny that it can make such sounds. It seems unlikely on
account of the extremely small size and softness of the book-louse, but
the matter needs further investigation.
[Illustration: FIG. 63.—The silver-fish insect (_Lepisma saccharina_).
The line to the right shows its natural size.]
A curious fact is that the grubs of beetles such as _Anobium_ and
_Xestobium_ (or other closely allied kinds) are not arrested in their
tunnelling by soft metal. They cannot tackle iron plate or brass
sheeting, but they will penetrate tinfoil and, what is more astonishing,
lead plate and leaden waterpipes. Specimens showing such perforations
are in the museums of Oxford and London, and I have received an account
of a lead pipe packed in wood in the wall of a house being perforated by
these beetle-grubs. Once at work on the wood, “the straightforward
intentions” of the grub are not to be diverted by such an obstacle as
lead: it goes straight on through the lead as it would through the cover
of a book or a knot in the wood.
[Illustration: FIG. 64.—The book-louse, or _Atropos divinatoria_, a
soft, cream-coloured, wingless insect smaller than a flea. It is
believed by some observers to be capable of making sounds like the
ticking of a watch.]
I have sometimes been asked to give advice as to the best method of
destroying the furniture worm or grub. If the piece of furniture (or its
pieces) can without injury be “baked” in a hot chamber for twenty-four
hours, at a temperature a little above that of boiling water, that is
the easiest method of destroying the pest. Or, again, I should suggest
placing the piece of furniture in a refrigerating chamber for a week or
two. If neither of these methods can be used, the piece of furniture
should be placed in a very hot room, and creosote or bisulphide of
carbon or solution of cyanide of potassium should be injected with a
very fine-nosed syringe into the little circular holes of the burrows on
the surface of the wood; then the piece of furniture must be at once
exposed to the cold, which will cause the air to be drawn into the
burrows and diffuse the volatile poison within. The “worm holes” on the
surface should, as soon as the piece of furniture is quite cold, be
closed by melted paraffin. If the piece of wood which it is desired to
“cure” will stand submersion in water for a few minutes, and is not
larger than a cricket bat, it is, of course, easy, by first warming it
through and then plunging it into water containing corrosive sublimate
or other poison, fairly to impregnate the burrows, and make an end of
the beetles and their grubs. Painting is the common and approved means
of protecting wood against these attacks, and in some positions metal
sheathing is used. The method most largely used for protecting wood in
the open air against “worm” and “mould” is that of forcing creosote into
its pores—an improvement on the old system of painting with coal tar. A
more expensive but beautiful method of protecting wood is to force hard
paraffin in a melted condition by pressure into the pores. The wood
becomes wonderfully firm and waterproof. Neither damp and mould, nor
boring insect, nor shrimp can then penetrate it. This method was
introduced some years ago, but I do not know whether it has been largely
used.
XXXIX
CHRISTMAS FARE