Spiders are generally considered as insects but they are actually not. They belong to a class of animals called arachnids. While insects are six legged creatures, arachnids are eight legged ones. Unlike insects spiders do not have an antenna either. Both arachnids and insects belong to a big class called arthropods.
Insects normally have three major body segments – head, thorax and abdomen. The eyes, mouth and the antenna belong to head segment, legs and wings are attached to thorax segment. Remaining organs are attached to abdomen segment. This segment is the end segment of the body connected to the thorax.
Arachnids on the other hand have two major body segments – cephalothorax (head and thorax together) and abdomen. Eyes, legs and jaws belong to cephalothorax. It is the fused head and thorax of an arachnid. The silk gland and other important organs belong to the abdomen segment. Arachnids live everywhere in from the green fields, wet swamps, desert regions to mountain tops. Insects have complex eyes. Though spiders have eight eyes, they do not have a good vision. They have tiny hairs on their legs which can sense any kind of vibration. Instead of using their vision, they use the sense of vibration sensed by tiny hairs on their legs.
The young of certain species climb up the plants and begin paying out strands of silk that are lifted into the air by slightest breeze.