Note: Information is dated. Do not rely on it.Spider. The common name of insect-like animals, constituting the order Araneida, of the class Arachnida. The head and the chest are united to form one segment known as a cephalothorax; no wings are developed; breathing is effected by means of pulmonary or lung sacs. The abdomen is unsegmented, and joined to the cephalothorax by a short narrow stalk; at the end of the abdomen are organs for spinning silk. The spider's web is usually intended to entangle prey (chiefly insects); but spiders also spin webs to make their abodes, and for other purposes. The legs number four pairs, and no antennae are developed. Their mandibles are terminated by a movable hook, flexed inferiorly, underneath which, and near its extremity, is a little opening that allows a passage to a venomous fluid contained in a gland of the preceeding joint. After wounding their prey with their hooked mandibles they inject this poison into the wound, which suddenly destroys the victim. The common garden or orb spider, with its geometrical web, is a very familiar species. To this family also belong the trap-door spiders, which excavate a nest in the ground, and fit to the aperture a curious little door or lid. The tarantulas are dark colored, hairy spiders living in tropical or sub-tropical countries. Some species of these are the largest spiders known, often reaching a length of five or six inches. Their sting is believed to be very poisonous.