Spiders are a special group within the arthropods called arachnids that also includes scorpions, ticks and mites.. They are like the other arthropods in that they have an outside skeleton made of chitin, they have jointed appendages and the three body regions of the head, thorax and abdomen. They have bilateral symmetry.
However, the spiders' group is different from the insects' group. Spiders have eight legs instead of six. Spiders do not have antennae. The spider's head and thorax are joined. Spiders have simple eyes made up of just one lens where insects have compound eyes with many lenses. Spiders have two sets of appendages connected to their heads. One pair is hollow and spews forth poison from glands in the spider's head. The other pair of appendages is used as feelers for the spider. The males also use the these feelers to store sperm cells during reproduction.
Spiders have eight eyes arranged on their heads. They breathe through organs called book lungs, so named because of their shape. Spiders have from two to four book lungs. There is a little opening in their abdomen that allows the air in.
Spiders have three pairs of appendages called spinnerets on the underside of their abdomens. Each spinneret has thousands of tubes. Liquid silk flows from the spider's silk glands through these tubes into the air where it becomes hard and forms a thread. The spiders use the threads to build its web and to make cocoons for its eggs.
Spiders usually reproduce in the summer or early fall. The female is larger than the male and frequently eats the male after mating. The female lays a large batch of eggs and then spins her cocoon. Frequently she dies after this. The eggs hatch in the winter and live inside the cocoon. The young spiders frequently eat each other. The ones that are still alive in the spring leave the cocoon.
Spiders mostly eat off of other insects, not eating them whole, but sucking juices out of them.
Spiders help man because they kill harmful Insects.
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