Spiders: amazing hunters and nature balancer

• The sex organ on a male spider is located at the end of one of its legs.
• Male spiders are usually smaller than female spiders.
• Most spiders are very nearsighted.
• Webs get dirty and torn, so lots of spiders make a new one every day.
• Spiders have as many as 8 eyes, but some spiders have only 6 eyes and several spiders have fewer or even none.
• Fear of spiders is called Arachnophobia.
• Most spiders have fangs, through which venom is ejected.
• Spiders are invertebrates, which means they don't have backbones.
• Spiders are not insects. Insects have three body parts and six legs.
• Spiders have eight legs and two body parts, the abdomen and the thorax.
• Spiders have silk spinning glands called spinnerets, at the tip of their abdomen.

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae

Spiders are air-breathing chelicerate arthropods that have two body segments, eight legs, and no chewing mouth parts. About 40,000 species have been identified. In spiders' bodies the usual arthropod segments are fused into two tagmata, the cephalothorax and abdomen, joined by a small, cylindrical pedicel. These small creatures help plants reproduce by pollinating them. They also help recycle dead trees and animals back into the earth. They are also a vital source of food for birds, fish, and small mammals. Without invertebrates, like spiders and insects, many other living things would not survive.

The silk of a spider is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images.

The largest spider is the South American tarantula, as big as a dinner plate and heavy as a stick of butter. The smallest is the Comb-footed spider, smaller than the head of a pin. The smallest, dwarf spiders of the subfamily Erigoninae, are less than 1 mm (about .05 inches) in body length. Cooked tarantula spiders are considered a delicacy in Cambodia, and by the Piaroa Indians of southern Venezuela – provided the highly irritant hairs, the spiders' main defense system, are removed first. Spider venoms may be a less polluting alternative to conventional pesticides as they are deadly to insects but the great majority are harmless to vertebrates. Australian funnel web spiders are a promising source as most of the world's insect pests have had no opportunity to develop any immunity to their venom, and funnel web spiders thrive in captivity and are easy to "milk". It may be possible to target specific pests by engineering genes for the production of spider toxins into viruses that infect species such as cotton bollworms. Possible medical uses for spider venoms are being investigated, for the treatment of cardiac arrhythmia, Alzheimer's disease, strokes, and erectile dysfunction.

Arachnophobia is a specific phobia, an abnormal fear of spiders or anything reminiscent of spiders, such as webs or spider-like shapes. It may be an exaggerated form of an instinctive response that helped early humans to survive, or perhaps a cultural phenomenon that is most common in predominantly European societies.