Spiders use this silk for all sorts of different purposes. In the first place, they use it for snaring insects.
The Garden-Spider
Let us take for an example, the web of the common garden-spider. It is to be seen in every garden, resting in the middle of its web; and you may always recognize it by the white cross upon its back. But I don't suppose that you have ever seen it spinning its net. For it always does so very early in the morning, generally beginning before sunrise, so that it may be quite ready for use as soon as the insects begin to fly.
First of all, the spider makes a kind of outer framework of very strong silken cords, and fastens it firmly in position by stout guy-ropes of the same material. Next, she carries a thread right across the middle and fixes it down on either side. Then, starting from the center, she carries thread after thread to the margin, carefully testing the strength of each by giving it two or three smart pulls, and fastening it firmly down. When she has finished this part of her task, the web looks like a badly shaped wheel.
The next thing that the spider does is to spin a little silken platform in the middle of her web to sit upon. And as soon as she has done this she begins to spin the spiral thread. Beginning from the center, she goes round and round and round, fastening the thread down every time that it crosses one of the straight cords—the spokes, as it were, of the wheel—until at last the web is finished. Then she goes to the little platform in the middle, and there remains, upside down, waiting for an insect to blunder into her net.
By and by, perhaps, a bluebottle fly does so. Then she shakes the web violently for a few moments, so as to entangle it more thoroughly, rushes down upon it, seizes it, and plunges her fangs into its body. But if she catches a wasp or a bee she nearly always cuts it carefully out, drops it to the ground, and then patches up the hole in her web. For she knows perfectly well that wasps and bees can sting!
Would you like to know why it is that flies stick to the web as soon as they touch it? The microscope shows us. All the way along, the spiral thread is set with very tiny drops of liquid gum. So tiny are these drops indeed, that there are between eighty and ninety thousand of them in a large web! And would you like to know why it is that the spider does not stick to the web as the flies do? Well, the fact is that only the spiral thread is set with these little gummy drops, and that as the spider runs about over her web she is most careful to place her feet only on the straight threads, and never on the spiral line. Other spiders, however, snare their prey in quite a different way.
The Marmignatto
This small spider, found on our western plains, is remarkable for feeding on large insects, such as grasshoppers and field-crickets, which it catches in an ingenious manner. It stretches a few silken threads across a narrow path way, quite close to the ground, along which these insects are likely to pass, and lies in wait just opposite until a grasshopper or a cricket approaches. When it comes to the threads the insect is sure to get at least one of its feet entangled. Then it stops, and tries to shake itself free. The only result of its struggles, of course, is that its other feet become entangled too; and while it is struggling the marmignatto springs upon its back, fastens a silken thread to it, springs down again, and fastens the other end to a grass-stem close by. Over and over again it does this, and before very long the unfortunate insect is firmly fastened down by hundreds of threads, and is quite unable to break free, or even to move one of its legs. Then the spider leaps upon its back once more, plunges its fangs into its body, and proceeds to suck its blood.
Hunting-Spiders