Spiders belong to a group of eight-legged animals. That makes them different from insects, which have six legs. They also have their bodies divided into two parts (insects are divided into three parts) and on the front part are the eyes and mouth and four pairs of walking legs. The back part contains the spider’s heart, and most of its guts.
Spiders are related to scorpions, mites and ticks. They are all hunters or ambushers. Some run along the ground to catch their prey. The the wolf spider can run very fast along the ground. Some make webs, and wait for insects to fly into them and get entangled in their sticky threads. These spiders sit on one of the threads so they know when an insect it has struck any part of the thread. They can then speed over to the insect before it has time to wriggle free. Some spiders make holes in the ground and make a web across the entrance. Others wait on grass stems or inside flowers to ambush their prey as it passes. The crab spider waits inside a flower and is camouflaged, so difficult to see. When an insect visits the flower the spider pounces on it.
The thread used for webs is the same thread spiders use to move from one branch to another. It is a long thread of material that is spun out of special glands on the underside of its body. The thread of material starts out as a liquid because it is under pressure inside the body, but it has the special property of turning to a solid when it is pulled, so as it leaves the gland it turns hard immediately. It does not have to wait until it has dried out.
Spiders make poison which they inject into their prey using fangs near their mouths. This does not kill the prey, but paralyses it and it stays alive until the spider is ready to eat it. Only the poison of a few species, such as the black widow spider, is harmful to humans.
Spiders have a very narrow gut, and cannot eat solid food. This means that they have to turn their food into a liquid and then suck it in. Spiders pump digestive fluids into the animal they are about to eat, literally dissolving it. They then suck the digested food.
You may wonder how spiders can live indoors or in a desert without any obvious access to water. They can do this because they get all of the water they need from their prey. They also have very efficient guts that remove all water from their waste, so what leaves a spider is a dry packet of waste.
Females lay up to 3,000 eggs in one or more silk egg sacs. Many females then protect the eggs by attaching them to their webs, hiding them in nests, or dragging them wherever they go.
Baby spiders hatch as spiderlings, which are very small spiders.
Spiders have to moult as they grow because their shell is hard. Most spiders live for only one to two years. Tarantulas, however, can live for over 20 years.
