SPIDERS AND THEIR WEBS—TRAP-DOOR SPIDERS—SPIDERS THAT EAT
BIRDS—AQUATIC SPIDERS—BORN IN A DIVING-BELL.
Though we have already had something to say about spiders, they are such
interesting creatures that we may as well devote a few pages more to
them—especially as the web, which is their most salient peculiarity, has
as yet hardly been mentioned. The beauty and ingenuity of this wonderful
fabric has always aroused the interest and admiration of mankind, and
will doubtless continue to do so, as long as spiders and men exist
together on the earth. Our own common garden or geometric spider is as
good a web-spinner, perhaps, as any that exists, or, if not, it is at
least as good as any that I can think of at the moment. Everyone is
familiar with the general appearance of the web and the mathematical
regularity of its outline, whilst all who have watched its construction
must have been astonished at the skill displayed by the spider, both in
the weaving and placing of it. It is composed of two separate parts,
the first, or framework, consisting of a number of stout, yet delicate,
cables, which radiate outwards from a common centre, whilst around them
a finer thread, quite distinct in its structure, is wound spirally,
in wider and wider circles, the last of which makes the circumference.
The quality of the thread, composing these two divisions of the web, is
as distinct as the parts themselves, for whereas “the radiating lines
are smooth and not very elastic, the spiral one is thickly studded
with minute knobs, and is elastic to a wonderful degree, reminding the
observer of a thread of india-rubber. It is to the little projections
that the efficacy of the net is due, for they are composed of a thick
adhesive and viscid substance, and serve to arrest the wings and legs
of the insects that happen to touch the net.”[12] “As the radii,” says
Mr. Blackwell (a great authority on British spiders), “are inadhesive,
and possess only a moderate share of elasticity, they must consist of a
different material from that of the viscid spiral line, which is elastic
in an extraordinary degree. Now, the viscidity of this line may be shown
to depend entirely upon the globules with which it is studded, for if
they be removed by careful application of the finger, a fine glossy
filament remains, which is highly elastic, but perfectly inadhesive. As
the globules, therefore, and the line on which they are disposed, differ
so essentially from each other, and from the radii, it is reasonable to
infer that the physical constitution of these several portions of the
net must be dissimilar. An estimate,” continues Mr. Blackwell, “of the
number of viscid globules distributed on the elastic spiral line, in a
net of _Epeira apoclisa_, of a medium size, will convey some idea of the
elaborate operations performed by the Epeira in the construction of
their snares. The mean distance between two adjacent radii, in a net of
this species, is about seven-tenths of an inch; if, therefore, the number
seven be multiplied by twenty (the mean number of viscid globules which
occur on one-tenth of an inch of the elastic spiral, at the ordinary
degree of tension), the product will be 140, the mean number of globules
deposited on seven-tenths of an inch of the elastic spiral line. This
product, multiplied by twenty-four, the mean number of circumvolutions
described by the elastic spiral line, gives 3,360, the mean number of
globules contained between two radii; which, multiplied by twenty-six,
the mean number of radii, produces 87,360, the total number of viscid
globules in a finished net of average dimensions. A large net, fourteen
or sixteen inches in diameter, will be found, by a similar calculation,
to contain upwards of 120,000 viscid globules, and yet _Epeira apoclisa_
will complete its snare in about forty minutes, if it meet with no
interruption.”
And yet, in the execution of these beautiful and elaborate webs,
the fine threads of which are placed with such nicety, and at such
regular distances one from another, that they have procured for their
manufacturers the specific title of “_geometric_,” the spider is guided
entirely by the sense of touch. This is proved by the fact that when
confined in total darkness it will spin webs as truly as by daylight;
but the test is hardly necessary, since, as the eyes of the spider are
situated on the front part of its head, whereas the threads issue from
the spinnarets at the extremity of its body and are guided by the hind
pair of legs, sight, it is evident, could hardly aid in the process.
Does reason, therefore, enter into the process of web-making, or is it
merely an instinctive one? This being a difficult question to answer,
instead of doing so I will quote the minute and interesting account given
by Thompson in his _Passions of Animals_ of how the spider spins its web
under ordinary conditions, premising, however, that, in almost every
point, different people, who all write as though they had been witnesses
of what they describe, appear to differ in their opinion. This remark
applies also to the structure of the thread itself, for whilst Wood and
Blackwell, as we have just seen, say that this differs essentially in the
two parts of the web, Kirby and Spence, who are followed by Professor
Romanes, believe it to be one and the same. Büchner, too, speaks of
the “high degree of elasticity” of the radii as against the “moderate
share” of it, which is all that Blackwell allows them, and so on—ample
encouragement this, surely, to observe spiders for ourselves, since
whatever we may think, there is sure to be someone respectable to agree
with us.
Thompson’s account is as follows: “The web of the garden spider—the most
ingenious and perfect contrivance that can be imagined—is usually fixed
in a perpendicular or somewhat oblique direction, in an opening between
the leaves of some plant or shrub; and as it is obvious that round its
whole extent lines will be required to which those ends of radii that
are farthest from the centre can be attached, the construction of those
exterior lines is the spider’s first operation. It seems careless about
the shape of the area they are to enclose, well aware that it can as
readily inscribe a circle in a triangle as a square; and in this respect
it is guided by the distance or proximity of the points to which it can
attach them. It spares no pains, however, to strengthen and keep them in
a proper degree of tension. With the former view it composes each line
of five or six, or even of more threads, glued together; and with the
latter it fixes to them from different points a numerous and intricate
apparatus of smaller threads; and having thus completed the foundation
of its snare, it proceeds to fill up the outline. Attaching a thread to
one of the main lines, it walks along it, guiding it with one of its
hind legs, that it may not touch in any part and be prematurely glued,
and crosses over to the opposite side, where, by applying its spinners,
it firmly fixes it. To the middle of this diagonal thread which is to
form the centre of its net, it fixes a second, which, in like manner,
it conveys and fastens to another part of the lines including the area.
The work now proceeds rapidly. During the preliminary operations it
sometimes rests, as though its plan required meditation; but no sooner
are the marginal lines of the net firmly stretched, and two or three
radii spun from its centre, than it continues its labour so quickly and
unremittingly that the eye can scarcely follow its process. The radii,
to the number of about twenty, giving the net the appearance of a wheel,
are speedily finished. It then proceeds to the centre, quickly turns
itself round, pulls each thread with its feet, to ascertain its strength,
breaking any one that seems defective, and replacing it by another.
Next it glues immediately round the centre five or six small concentric
circles, distant about half a line from each other, and then four or
five larger ones each separated by the space of half an inch or more.
These last serve as a sort of temporary scaffolding to walk over, and to
keep the radii properly stretched, while it glues to them the concentric
circles that are to remain, which it now proceeds to construct. Placing
itself at the circumference, and fastening its thread to the end of one
of the radii, it walks up that one towards the centre to such a distance
as to draw the thread from its body of a sufficient length to meet the
next. Then stepping across and conducting the thread with one of its hind
legs, it glues it with its spinners to the point in the adjoining radius
to which it is to be fixed. This process it repeats until it has filled
up nearly the whole space from the circumference to the centre with
concentric circles, distant from each other about two lines. It always,
however, leaves a vacant interval around the smallest first-spun circles
that are nearest to the centre, and bites away the small cotton-like
tuft that united all the radii, which being held now together by the
circular threads have thus, probably, their elasticity increased; and in
the circular opening resulting from this procedure it takes its station
and watches for its prey, or occasionally retires to a little apartment
formed under some leaf, which it also uses as a slaughter-house.”
The lair thus formed is connected with the web by means of a thread
along which the vibrations caused by the struggles of any captured insect
are carried, thus apprising the spider, who, if angry, rushes out to
seize her victim. It is a very amusing thing to strike a tuning-fork on
some hard substance, and then touch the net with it. The spider, full of
excitement, darts towards the area of disturbance, but is bewildered at
finding nothing, where the bag seemed so obvious. She may be thus lured
out several times in succession, but at length does not come, showing
that she can adapt her psychology to an experience which must be for her
altogether unprecedented. I have compared her, on these occasions, with a
sceptic at a _séance_, when something had unmistakably and unaccountably
happened.
More interesting, perhaps, even than the making of the web, is the way
in which the spider will sometimes weight it in order to make it steady
when a high wind is blowing. There is no doubt about this, as it has been
observed by many persons on as many different occasions. I will therefore
quote an account at second-hand, as it was given to the late Mr. Wood by
one of his friends who was accustomed to watch spiders in his verandah.
“One day,” says Wood, “a sharp storm broke out and the wind raged so
furiously through the garden that the spiders suffered damage from it,
although sheltered by the verandah. The mainyards of one of these webs,
as the sailors would call them, were broken, so that the web was blown
hither and thither, like a slack sail in a storm. The spider made no
fresh threads, but tried to help itself in another way. It let itself
down to the ground by a thread and crawled to a place where lay some
splintered pieces of a wooden fence thrown down by the storm. It fastened
a thread to one of the bits of wood, turned back with it, and hung it
with a strong thread to the lower part of its nest, about five feet from
the ground. The performance was a wonderful one, for the weight of the
wood sufficed to keep the nest tolerably firm, while it was yet light
enough to yield to the wind and so prevent further injury. The piece of
wood was about two and a half inches long, and as thick as a goose quill.
On the following day a careless servant knocked her head against the wood
and it fell down. But in the course of a few hours the spider had found
it and brought it back to its place. When the storm ceased, the spider
mended her web, broke the supporting thread in two, and let the wood
fall to the ground.” What, it may be asked, could a man have done more?
If people were really governed by evidence in their opinions on a great
many subjects—for that they are is one of the greatest fallacies in the
world—this one case would be sufficient to establish the reasoning powers
of all animals standing not lower in the scale than spiders, whilst
other instances as good lower down would take it up to them in the same
way. But one really believes according to one’s wishes, and it is quite
surprising that this fact—which can be verified by anyone—is not more
generally recognised than it is.
Wonderful as are the webs which are spun by many spiders for the purpose
of entrapping their prey, the houses which some of them make and live
in, are, perhaps, even more extraordinary. The trap-door spiders inhabit
various parts of the world, but are found in most abundance, or, at
least, have attracted most attention, in the island of Jamaica. They, all
of them, make a long tunnel or gallery, going down at a steep slant into
the earth, and round the sides of this they spin a close web, which makes
a strong, durable lining. This lining is double, and whilst the inner
layer is soft and smooth like silk, the outer one, in which the spider
lives, is so rough and flaky that it both looks and feels more like
felt, or rough paper, or the bark of a tree, than a substance usually so
delicate as the web of a spider. This roughness, however, is just what
is required, since it enables the spider to run up and down its little
tube, or tunnel, with the greatest ease. But the most wonderful part of
this ingenious dwelling is the trap-door, at its entrance, from which the
spider takes its name, and by which it has become famous. This, also, is
woven by the spider, and is one in substance with the tube, to which it
forms a little door, or lid, which fits its orifice as exactly as does
the lid of a neatly made box. Like a box, too, it is attached to the tube
by a hinge, the web, at the jointure, being spun in such a manner that we
may well give it this name. Before the spider can either enter or leave
its tube, the lid of it has to be lifted, and both the creature and its
dwelling become, then, conspicuous objects. Once in or out, however,
the lid drops, and as it fits into, as well as over, the orifice, there
is then no break in the surface of the ground. Still, if the lid were
made only of web, it would be discernible by close observation, since a
little round patch of another material would be, as it were, let into the
ground. The spider, however, as if fearing this, covers the exterior of
the lid with earth which it brings from near about, and by the use of a
gummy secretion which it has the power of exuding, causes to adhere to
it. The lid, therefore, becomes practically a part of the surrounding
earth, from which, when no longer raised above its surface, it is
impossible to distinguish it.
If, however, in spite of these artifices, its dwelling should be
discovered, the spider, ascending to the mouth of the tube, pulls upon
the lid so as to prevent, if possible, its being raised. Mr. Moggridge,
who made a study of trap-door spiders, and has written a work upon
them, says: “No sooner had I gently touched the door with the point of
a penknife than it was drawn slowly downwards with a movement which
reminded me of the tightening of a limpet on a sea-rock, so that the
crown, which at first projected a little way above, finally lay a little
below the surface of the soil. I then contrived to raise the door very
gradually, despite the strenuous efforts of the occupant, till at length
I was just able to see into the nest and to distinguish the spider
holding on to the door with all her might, lying back downwards, with her
fangs and all her claws driven into the silk lining of the under surface
of the door. The body of the spider was placed across, and filled up the
tube, the head being away from the hinge, and she obtained an additional
purchase in this way by blocking up the entrance.” When a trap-door
spider uses its claws like this to pull down the lid of its tube, they
make little holes all round the edge of the inside of the lid. They can
be seen, if one looks, quite plainly, and look as if the points of little
pins had been stuck into the smooth surface of the web.
Some trap-door spiders are of a large size, and when they lift up the
lids of their tunnels, and look cautiously out, they have quite a
formidable appearance. During the night, they leave their home, and hunt
about for insects of various kinds. As soon as they have caught one
they carry it into their dens and devour it there at their leisure. The
Rev. Mr. Wood gives an amusing description of this spider’s actions.
“New-comers,” he says, “into the country which the trap-door spider
inhabits, are often surprised by seeing the ground open, a little lid
lifted up, and a rather formidable spider peer about as if to reconnoitre
the position before leaving its fortress. At the least movement on the
part of the spectator, back pops the spider, like the cuckoo on a clock,
clapping its little door after it quite as smartly as the wooden bird,
and, in most cases, succeeds in evading the search of the astonished
observer, the soil being apparently unbroken, without a trace of the
curious little door that had been so quickly shut.”
Some tropical spiders are of very great size, so that, in Brazil,
children sometimes tie one end of a piece of string round their waist,
and lead them about as if they were dogs. This does not mean, of course,
that they are quite so big as dogs—even little ones—but the legs of a
very huge mygale, as these monsters are called, might have a spread as
big as a man’s hand, and the body would be then, perhaps, not so very
much smaller than a mouse’s. That the webs made by such immense spiders
as these should be strong enough to hold a small bird, and that, when
caught, the bird should be eaten as flies are by spiders here at home,
does not seem so very remarkable—in fact, it is just what one might
reasonably expect.
[Illustration: CURIOUS PETS.
Brazilian children tie one end of a piece of string round the waist of
Mygales and lead them about as if they were dogs.]
But naturalists, for the most part, are a very unimaginative, sceptical
set of men, with whom not to believe a thing, if it is, in the smallest
degree, striking or picturesque, is a sort of virtue, in which they hug
themselves as long as they can. Accordingly, when Madame Merian and
Palisot de Beauvois told them that these large spiders really did eat
birds, they all set their faces against it, and were determined not to
credit an account derived from the reports of natives, who, of all people
in the world, were thought the least likely to know anything about the
animals which lived in their own country. It is strange how this idea—or
some other one which comes to practically the same thing—prevails. It is
as strong to-day as ever, yet in ninety-nine cases out of a hundred, what
the natives say turns out to be true. At last some European happens to
see, once, what they have seen and known all their lives. Then, perhaps,
the natives are believed, but only, as it were, in the wake of the one
European, who gets more credit for finding they were right than they do
for having always told the truth. The one European, in this instance,
was Mr. H. W. Bates, who, in his well-known work _The Naturalist on the
River Amazon_, gives the following account of what he saw: “At Cameta I
chanced to verify a fact relating to the habits of a large hairy spider
of the genus Mygale, in a manner worth recording. The species was _M.
avicularia_, or one very closely allied to it. The individual was nearly
two inches in length of body, but the legs expanded seven inches, and the
entire body and legs were covered with coarse grey and reddish hairs.
I was attracted by a movement of the monster, on a tree-trunk; it was
close beneath a deep crevice in the tree, across which was stretched a
dense, white web. The lower part of the web was broken, and two small
birds—finches—were entangled in the pieces; they were about the size of
the English siskin, and I judged the two to be male and female. One of
them was quite dead, the other lay under the body of the spider, not
quite dead, and was smeared with the filthy liquor or saliva, exuded by
the monster. I drove away the spider and took the birds, but the second
one soon died.”
Several spiders have taken to a more or less aquatic life. One of
these—the raft-spider—makes, as its name implies, a sort of raft of dry
leaves, sticks, etc., which it fastens together by means of its web, and
then launches itself on the water, where it is blown about as the wind
listeth. When an aquatic insect comes to the surface of the stream, or
when a moth or fly falls into it, the spider runs along the water, and
seizes it, after which it returns to its raft; or it will run down the
stems of the water-plants, and seize what it finds clinging to them,
returning with them, or when it requires a fresh supply of air, as
before. If threatened with any danger it crawls underneath its raft, and
there remains until all is safe again.
Still more ingenious are the _façons d’agir_ of the water-spider, which
weaves a nest like a diving-bell against some sub-aquatic plant, and
fills it with air from above, by carrying down bubbles that cling to the
hairs of its body. It used to be thought that this air had exuded from
the stems of the plant itself, and so filled the nest affixed to them,
but the naturalist Bell, so long ago as 1856, proved that this was not
the case, and that the spider brings down its own air, by experiments, of
which he gave the following interesting accounts:—
“No. 1. Placed in an upright cylindrical vessel of water, in which was a
rootless plant of Stratiotes, on the afternoon of November 14th. By the
morning it had constructed a very perfect oval cell, filled with air,
about the size of an acorn, on this it has remained stationary up to the
present time.
“No. 2. November 15th. In another vessel, also furnished with Stratiotes,
I placed six Argyronetræ (water-spiders). The one now referred to began
to weave its beautiful web, about five o’clock in the afternoon. After
much preliminary preparation it ascended to the surface, and obtained
a bubble of air with which it immediately, and quickly, descended, and
the bubble was disengaged from the body and left in connection with the
web. As the nest was on one side, in contact with the glass, enclosed in
an angle formed by two leaves of the Stratiotes, I could easily observe
all its movements. Presently, it ascended again, and brought down
another bubble, which was similarly deposited. In this way no less than
fourteen journeys were performed, sometimes two or three very quickly
one after another; at other times with a considerable interval between
them, during which time the little animal was employed in extending and
giving shape to the beautiful transparent bell, getting into it, pushing
it out at one place, and amending it at another, and strengthening its
attachments to the supports. At length it seemed to be satisfied with its
dimensions, when it crept into it, and settled itself to rest, with the
head downwards. The cell was now the size and nearly the form of half an
acorn cut transversely, the smaller and rounded part being uppermost....
The manner,” continues Bell, “in which the spider possesses itself of
the bubble of air is very curious, and, as far as I know, has never been
exactly described. It ascends to the surface slowly, assisted by a thread
attached to the leaf or other support, below, and to the surface of the
water. As soon as it comes near the surface, it turns with the extremity
of the abdomen upwards, and exposes a portion of the body to the air,
for an instant, then with a jerk, it snatches, as it were, a bubble of
air, which is not only attached to the hairs which cover the abdomen, but
is held on by the two hinder legs, which are crossed at an acute angle,
near their extremity, this crossing of the legs taking place the instant
the bubble is seized. The little creature then descends more rapidly and
regains its cell, always by the same route, turns the abdomen within it,
and disengages the bubble.”
To its home thus ingeniously constructed the water-spider brings whatever
prey it catches. Here too it lays and arranges its eggs, which are in
due time hatched, so that, though an air-breathing animal, it is both
born and passes the earliest days of its life beneath the surface of the
water—a curious apparent, though not a real, contradiction.