Spiders

Teacher's Story

HE spiders are the civil engineers among the small inhabitants of our fields and woods. They build strong suspension bridges, from which they hang nets made with exquisite precision; and they build aeroplanes and balloons, which are more efficient than any that we have yet constructed; for although they are not exactly dirigible, yet they carry the little balloonists where they wish to go, and there are few fatal accidents. Moreover, the spiders are of much economic importance, since they destroy countless millions of insects every year, most of which are noxious—like flies, mosquitoes, bugs and grasshoppers.

There is an impression abroad that all spiders are dangerous to handle. This is a mistake; the bite of any of our common spiders is not nearly so dangerous as the bite of a malaria-laden mosquito. Although there is a little venom injected into the wound by the bite of any spider, yet there is no species found in the Northern States whose bite is sufficiently venomous to be feared.

There is no need for studying the anatomy of the spider closely in nature-study. Our interest lies much more in the wonderful structures made by the spiders, than in a detailed study of the little creatures themselves.

Our house spiders are indefatigable curtain-weavers. We never suspect their presence, until suddenly their curtains appear before our eyes, in the angles of the ceilings—invisible until laden with dust. The cobwebs are made of crisscrossed lines, which are so placed as to entangle any fly that comes near. The lines are stayed to the sides of the wall and to each other quite firmly, and thus they are able to hold a fly that touches them. The spider is likely to be in its little den at the side of the web; this den may be in a crevice in the corner or in a tunnel made of the silk. As soon as a fly becomes entangled in the web the spider runs to it, seizes it in its jaws, sucks its blood, and then throws away the shell, the wings and legs. If a spider is frightened, it at first tries to hide and then may drop by a thread to the floor. If we catch the little acrobat it will usually "play possum" and we may examine it more closely through a lens. We shall find it is quite different in form from an insect. First to be noted, it has eight legs; but most important of all, it has only two parts to the body. The head and thorax are consolidated into one piece, which is called the cephalothorax. The abdomen has no segments like that of the insects, and is joined to the cephalothorax by a short, narrow stalk. At the front of the head is the mouth, guarded by two mandibles, each ending in a sharp claw, at the tip of which the poison gland opens. It is by thrusting these mandibles into its prey that it kills its victims. On each side of the mandible is a palpus, which in the males is of very strange shape. The eyes are situated on the top of the head. There are usually four pairs of these eyes, and each looks as beady and alert as if it were the only one.

The spinning organs of the spider are situated near the tip of the abdomen, while the spinning organ of the caterpillar is situated near its lower lip. The spider's silk comes from two or three pairs of spinnerets which are fingerlike in form, and upon the end of each are many small tubes from which the silk is spun. The silk is in a fluid state as it issues from the spinnerets, but it hardens immediately on contact with the air. In making their webs, spiders produce two kinds of silk, one is dry and inelastic, making the framework of the web; the other is sticky and elastic, clinging to anything that it touches. The body and the legs of spiders are usually hairy.

Method—The pupils should have under observation a cobweb in a corner of a room, preferably with a spider in it.

3. If a fly becomes tangled in a web, describe the action of the spider. Does the spider eat all of the fly? What does it do with the remains?

4. If the spider is frightened, what does it do? Where does the silken thread come from, and how does its source differ from the source of the silken thread spun by caterpillars?

5. Imprison a spider under a tumbler or in a vial, and look at it very carefully. How many legs has it? How does the spider differ from insects in this respect? How many sections are there to the body? How does the spider differ from insects in this respect?

6. Look closely at the head. Can you see the hooked jaws, or fangs? Can you see the palpi on each side of the jaws? Where are the spider's eyes? How many pairs has it?