Really Cool Facts: The weight of insects eaten by spiders every year is greater than the total weight of the entire human population. It has been estimated that there can be up to nearly 5 million spiders per hectare. The combined length of thread in a spider's web is about 20-60 m and it can take the spider up to 3 hours to make an average sized web. On an equal weight basis, spider silk is twice as strong as steel and very elastic.

Arthropoda: Within the huge group called animals are many that have no backbones. These are called invertebrates. The invertebrates include mostly small animals. One major group or phylum of invertebrates is called the Arthropoda. Biologists include insects and spiders in this group.

Spiders are not insects. Why not?: Insects have bodies with three main parts--head, thorax, and abdomen. The head has eyes, antennae and mouthparts. The thorax has three pairs of legs. The entire body is protected by a tough outer covering called an exoskeleton. Spiders have only two main body parts. The body consists of a combined head and thorax called the cephalothorax, and the abdomen. The cephalothorax has the eyes, mouthparts (no antennae) and four pairs of legs. Animals that share these characteristics include ticks, mites, scorpions and spiders. The group is called the Arachnida.

What - and how - do spiders eat? All spiders are carnivorous, Most spiders eat insects but a few of the larger species are big enough to prey on small vertebrate animals like mice or small birds. Most spiders' jaws work from side to side. They have toothed edges used in breaking up the prey during feeding.

How many eyes do spiders have? Most spiders have eight simple eyes. [Insects on the other hand have large, compound eyes.] The two main eyes of a spider each have a simple lens, and a retina which is made up of light sensitive cells whose surfaces point toward he light as it enters the eye. These main eyes have a small field of vision with high resolution. They are especially well developed in jumping spiders. A spider's secondary eyes are light sensitive and are used to detect shadows and the difference between light and dark.

How are spider webs made? Spider webs are made of continuous strands of spider silk produced from about six silk glands beneath the abdomen. A web-spinning spider first constructs a web framework attached to parts of plants or other firm supports. This framework has threads radiating out from the center. Next, the spider will work from the edge of the web toward the center laying down a spiral of sticky threads.

What is spider silk made of? Spider silk is a protein that is formed as a liquid by silk glands and squeezed out of spinnerets like toothpaste from a tube. The liquid thread hardens as it leaves the spinneret and some types of such thread become stronger than a steel thread of the same diameter. Most of the silk threads in a spider web are multiple strands of fine silk lying alongside each other. Spiders produce several types of silk from different types of spinning glands.

Why doesn't a spider stick to his own web? The spider holds to the silk thread with claw-like bristles on its legs. Its body oil keeps it from sticking to the web. A moth is protected from the sticky strand by scales on its body. Most garden spiders hide during the day then recline in their web at night.

Different webs for different spiders? Spiders that spin an orb-shaped web are classified as Orb-Web Spiders. The wheel shaped web is used to catch prey that flies into the sticky silk. The web vibration announces a 'catch' and the spider rushes to tie up the victim before it gets away or tears up the web. Sometimes the male Orb spider comes calling and will shake the strands of silk to announce his arrival.

Do all spiders have webs? No. The trap-door spider lives in a hole in the ground. It lines its nest with silk then weaves a trap door of silk. The door is camouflaged with moss or grass. But if an insect steps on the door, it opens and the insect falls inside to become the spider's meal.

How many different types of spiders are there? There are now about 35,000 named species of spiders worldwide. This includes about 3,000 species in North America. Biologists and naturalists believe that there are many more species of spiders still to be identified and named.