Spider belongs to phylum Arthropoda, class Arachnida, order Araneae. This order has 3 sub-orders. The Mygalomorphae (the primitive spiders), the Aranaeomorphae (the modern spiders) and the Mesothelae, with one family of spiders the Liphistiidae. Every spider belongs to a family, which is further divided into genus, followed by species. As a rule genus and species are printed in italics.

Spiders are characterized by the following Eight walking legs , two main body parts Cephalothorax and abdomen, jaws adapted for tearing or piercing prey , 6 to 8 simple eyes and a skeleton outside the body

Spider body parts

Spider has two distinct body parts. The first consists of a fused head and breast called as cephalothorax. It is made from a hardened material, called chitin. The second, rear part is the soft abdomen, called opisthosoma. A tiny tube called pedicel connects the cephalothorax and abdomen.

The eight legs, the two jaws (chelicerae) and the two feelers (palps) are connected to the cephalothorax. The males have a bulb at the end of their palps. These are filled with semen before copulation and are used to inject the semen into the sexual organs of the female.

The brains are located in the cephalothorax and the heart at the front upper side of the abdomen. The back or top of a spider is the dorsal side and at the bottom is called the ventral side. The genitals of the spider (epigynum) are located just behind the legs on the ventral side. The silk making spinners (white) are located at the rear of the abdomen. The book lung / trachea are enclosed in the abdomen.

Jaws and fangs

Primitive spiders, Mygalomorphae, have forwardly pointing jaws that move forwards and backward in contrast to the modern spider. Therefore they can not crunch a prey. They wait until the prey contents are dissolved before they can suck it empty.

Modern spiders crunch their catch with their jaws. Some spiders wrap their prey in silk, taking care that the victim does not bite them. Crab spiders do not use silk but use a rapid working poison. The injected enzymes dissolve the prey and then it is sucked empty.

Spider Skin

The spider body is covered with a more or less rigid exoskeleton made of protein and chitin. To allow the spider to grow the entire cuticle must be shed periodically in a process known as moulting. A new larger cuticle is first made underneath the old one, the old one splits and the spider climbs out. The new cuticle is very soft and most spiders will not move until the cuticle hardens. Spiders can often be seen with one or more missing legs. After moulting these lost legs regenerate. After the first change of skin, newly formed legs are smaller than the original legs. After the second moulting these differences in length are hardly observable.

A spider does not have ears. A spider hears with very tiny hairs on her legs (thrichobotria). She can localize the origin of a sound by interpreting the movement of the air produced.

The eyes of spider differ greatly between families. Spiders who hunt without a web like wolf spiders (Lycosidae), lynx spiders Oxyopidae) and jumping spiders ( Salticidae ) have a well-developed eyesight. Jumping spiders can see nearly as well as humans. Experiments have shown that they are even capable of seeing colors. Cave spiders, which live in the dark, have no or hardly any eyesight. They depend completely on sound and feeling.

Web and silk

Normally a spider has three pairs of spinners, but there are spiders with just one pair or as many as four pairs. Every spinner has it own function.

The human eye is capable of detecting objects at a distance of 10 cm with a diameter of 25 µm. The average diameter of a thread in an orb web is around 0.15 µm. We see see the web only because of the reflection of sunlight on the thread. Howver these thin wires are capable of stopping a bee flying at full speed.

Spiders produce three different types of webs. The sheet web, the orb web and the spatial web. The most well known form is the orb web.

How is this web constructed? The most difficult part is the construction of the first thread. The spiders lets go of a piece of thread from the spinnerets. The wind carries this while making the thread longer and longer. It sticks to a spot. Then she walks carefully over the thread, strengthening it with a second thread. This is repeated until the primary thread is strong enough. After this, she hangs a thread in the form of a Y below the primary thread. These are the first three radial of the web. More radials are then constructed taking care that the distance between the radial is small enough to cross. Then non-sticky circular construction spirals are made. The web is completed when the adhesive spiral threads are placed. While the sticky spirals are placed the non-sticky spirals are removed.

Reproduction

Males are often smaller and more coloured than the females. Males can be recognized by what seems to be the fifth pair of legs. These are the palps with bulbs they use to inject sperm in the genital openings of a female. Prior to copulation a male fills its bulbs with sperms by weaving a small web. On the web he drops some droplets of sperm from its genitals and sucks the sperm into the bulbs.

After mating, the males of some species must be extremely careful. Sometimes the female tries to kill the male for an easy meal. Often the male escapes. The males of some species do not care anymore to live longer and are eaten without objection. Other species live together happily for a long time after mating.

Some females die after the eggs have hatched and some females are even eaten by their offspring. Others may live on for years. Most females guard their eggs and youngsters. Wolf spiders carry their egg-sac at their spinners and carry the young on their backs until their first change of skin. Orb weavers often guard their egg sac.