THE BUILDING OF A SPIDER’S WEB
The smallest garden contains the Garden Spiders, all clever weavers.
Let us go every evening, step by step, from one border of tall
rosemaries to the next. Should things move too slowly, we will sit down
at the foot of the shrubs, where the light falls favorably, and watch
with unwearying attention. Let us give ourselves a title, “Inspector of
Spiders’ Webs!” There are not many people in that profession, and we
shan’t make any money by it; but never mind, we shall learn some very
interesting things.
The Spiders I watch are young ones, much slenderer than they will be in
the late autumn. They work by day, work even in the sun, whereas the
old ones weave only at night. Work starts in July, a couple of hours
before sunset.
The spinstresses of my inclosures then leave their daytime
hiding-places, choose their posts and begin to spin, one here, another
there. There are many of them; we can choose where we please. Let us
stop in front of this one, whom we surprise in the act of laying the
foundations of her web. She runs about the rosemary hedge, from the tip
of one branch to another, within the limits of some eighteen inches.
Gradually, she puts a thread in position, drawing it from her body with
the combs attached to her hind-legs. She comes and goes impetuously,
as though at random; she goes up, comes down, goes up again, dives
down again and each time strengthens the points of contact with
threads distributed here and there. The result is a sort of frame. The
shapeless structure is what she wishes; it marks out a flat, free, and
perpendicular space. This is all that is necessary.
A special thread, the foundation of the stronger net which will be
built later, is stretched across the area of the other. It can be told
from the others by its isolation, its position at a distance from any
twig that might interfere with its swaying length. It never fails to
have, in the middle, a thick white point, formed of a little silk
cushion.
The time has come to weave the hunting-snare. The Spider starts from
the center, which bears the white signpost, and, running along the
cross-thread, hurriedly reaches the circumference, that is to say, the
irregular frame inclosing the free space. Still with the same sudden
movement, she rushes from the outside to the center; she starts again
backwards and forwards, makes for the right, the left, the top, the
bottom; she hoists herself up, dives down, climbs up again, runs down
and always returns to the central landmark by roads that slant in the
most unexpected manner. Each time a radius or spoke is laid, here,
there, or elsewhere, in what looks like mad disorder.
[Illustration]
Any one looking at the finished web, so neat and regular in appearance,
would think that the Spider laid the spokes in an orderly fashion, one
after the other. She does nothing of the sort, but she knows what she
is about, all the same. After setting a few spokes in one direction,
the Spider runs across to the other side to draw some in the opposite
direction. These sudden changes have a reason; they show us how clever
the Spider is in her business. If she began by laying all the spokes on
one side, she would pull the web out of shape or even destroy it. She
must put some on the other side to balance. She is a past mistress of
the secrets of rope-building, without serving an apprenticeship.
One would think that this interrupted and apparently disordered
labor must result in a confused piece of work. Wrong: the rays are
equidistant and form a beautifully regular circle. Their number is a
characteristic mark of the different species. The Angular Epeira places
twenty-one in her web, the Banded Epeira thirty-two, the Silky Epeira
forty-two. These numbers are not absolutely fixed; but the variation is
very slight.
Now which of us would undertake, offhand, without much preliminary
experiment and without measuring-instruments, to divide a circle into a
given quantity of sectors or parts of equal width? The Garden Spider,
though weighted with a wallet and tottering on threads shaken by the
wind, performs the delicate division without stopping to think. She
achieves it by a method which seems mad according to our notions of
geometry. Out of disorder she brings order. We are amazed at the result
obtained. How does this Spider come to succeed with her difficult
problem, so strangely managed? I am still asking myself the question.
The laying of the radii or spokes is finished. The Spider takes her
place in the center, on the little cushion. Stationed on this support,
she slowly turns round and round. She is engaged on a delicate piece of
work. With an extremely thin thread, she describes from spoke to spoke,
starting from the center, a spiral line with very close coils. This is
the center of the web. I will call it the “resting-floor.”
The thread now becomes thicker. The first could hardly be seen; the
second is plainly visible. The Spider shifts her position with great
slanting strides, turns a few times, moving farther and farther from
the center, fixes her line each time to the spoke which she crosses,
and at last comes to a stop at the lower edge of the frame. She has
described a spiral with coils of rapidly-increasing width. The average
distance between the coils, even in the webs of the young Spiders, is
about one third of an inch.
This spiral is not a curved line. All curves are banished from
the Spiders’ work; nothing is used but the straight line and its
combinations. This line forms the cross-bars, or supporting rungs,
connecting the spokes, or radii.
All this is but a support for the snaring-web. Clinging on the one
hand to the radii, on the other to the cross-bars, the Spider covers
the same ground as when laying the first spiral, but in the opposite
direction: formerly, she moved away from the center; now she moves
towards it and with closer and more numerous circles. She starts from
the end of the first spiral, near the outside of the web.
What follows is hard to observe, for the movements are very quick and
jerky, consisting of a series of sudden little rushes, sways, and bends
that bewilder the eye. The two hind-legs, the weaving implements, keep
going constantly. One draws out the thread from the spinneret, and
passes it to the other, which lays it on the radius. As soon as the
radius is touched, the thread sticks to it by its own glue.
[Illustration]
The Spider, without a stop of any kind, turns and turns and turns,
drawing nearer to the center and always fixing her thread at each spoke
which she crosses. At last, at some distance from the center, on the
edge of what I have called the resting-floor, the Spider suddenly ends
her spiral. She next eats the little cushion in the center, which is a
mat of ends of saved silk. She does this to economize silk, for after
she has eaten it the cushion will be turned into silk for the next web
she spins.
Two Spiders, the Banded and the Silky, sign their work by laying a
broad white ribbon in a thick zigzag from the center to the lower edge
of the web. Sometimes they put a second band of the same shape, but a
little shorter, opposite the first, on the upper part of the web.
[Illustration]
THE STICKY SNARE
The spiral part of the Garden Spider’s web is a wonderful contrivance.
The thread that forms it may be seen with the naked eye to be different
from that of the framework and the spokes. It glitters in the sun,
and looks as though it were knotted. I cannot examine it through the
microscope outdoors because the web shakes so, but by passing a sheet
of glass under the web and lifting it I can take away a few pieces of
thread to study. The microscope now shows me an astounding sight.
Those threads, so slender as to be almost invisible, are very closely
twisted twine, something like the gold cord of officers’ sword-knots.
Moreover, they are hollow. They contain a sticky moisture resembling a
strong solution of gum arabic. I can see it trickling from the broken
ends. This moisture must ooze through the threads, making them sticky.
Indeed, they are sticky. When I lay a straw flat upon them, it adheres
at once. We see now that the Garden Spider hunts, not with springs, but
with sticky snares that catch everything, down to the dandelion-plume
that barely brushes against the web. Nevertheless, the Spider herself
is not caught in her own snare. Why?
For one thing, she spends most of her time on her resting-floor in the
middle of the web, which the spiral does not enter. The resting-floor
is not at all sticky, as I find when I pass a straw against it. But
sometimes when a victim is caught, perhaps right at the end of the web,
the Spider has to rush up quickly to bind it and overcome its attempts
to free itself. She seems to be able to walk upon her network perfectly
well then. Has she something on her feet which makes them slip over the
glue? Has she perhaps oiled them? Oil, you know, is the best thing to
prevent surfaces from sticking.
I pull out the leg of a live Spider and put it to soak for an hour in
disulphide of carbon, which dissolves fat. I wash it carefully with a
brush dipped in the same fluid. When the washing is finished, the leg
sticks to the spiral of the web! We see now that the Spider varnishes
herself with a special sweat so that she can go on any part of her web
without difficulty. However, she does not wish to remain on the spiral
too long, or the oil might wear away, so most of the time she stays on
her safe resting-floor.
This spiral thread of the Spider’s is very quick to absorb moisture,
as I find out by experiment. For this reason the Garden Spiders, when
they weave their webs in the early morning, leave that part of the work
unfinished, if the air turns misty. They build the general framework,
they lay the spokes, they make the resting-floor, for all these parts
are not affected by excess moisture; but they are very careful not to
work at the sticky spiral, which, if soaked by the fog, would dissolve
into sticky threads and lose its usefulness by being wet. The net that
was started will be finished to-morrow, if the weather is right. But on
hot days this property of the spiral is a fine thing; it does not dry
up, but absorbs all the moisture in the atmosphere and remains, at the
most scorching times of day, supple, elastic, and more and more sticky.
What bird-catcher could compete with the Garden Spider in the art of
laying snares? And all this industry and cunning for the capture of a
Moth!
Then, too, what a passion the Spider has for production. I calculated
that, in one sitting, each time that she remakes her web, the Angular
Spider produces some twenty yards of gummy thread. The more skillful
Silky Spider produces thirty. Well, during two months, the Angular
Spider, my neighbor, renewed her snare nearly every evening. During
that time she manufactured something like three quarters of a mile of
this tubular thread, rolled into a tight twist and bulging with glue.
We cannot but wonder how she ever carries so much in her little body,
how she manages to twist her silk into this tube, how she fills it with
glue! And how does she first turn out plain threads, then russet foam,
for her nest, then black stripes to adorn the nest? I see the results,
but I cannot understand the working of her factory.
[Illustration]