What is a spider?
Anatomy
Reproduction
Silk
What is a Spider?
A spider is a predatory invertebrate animal with eight legs and two body parts, and no wings. They are often confused as being insects, but all spiders have 8 legs, unlike insects which have 6.
Spiders usually have silk-spinning organs at the back end of the body which they use to spin silk to construct cocoons for eggs or traps and webs for prey.
A spider is any member of the arachnid order Araneae, an order divided into three sub-orders: the Mygalomorphae (primitive spiders), the Araneomorphae (modern spiders) and the Mesothelae, which contains the Family Liphistiidae, containing rarely seen burrowing spiders from Asia.
All spiders are carnivores. They eat other species of arthropods including mites, crustaceans, mice, skinks and even other spiders.
The study of spiders is known as arachnology, although it is often included in the more general term entomology. REF5
Spider’s scientific class, Arachnida, is named for the Greek tapestry weaver Arachne, who was turned into a spider by the goddess Athena. REF6
Anatomy:
The anatomy of a spider consists of four pairs of legs and a body divided into two parts, the cephalothorax (front) and the abdomen (rear), connected by a thin pedicel or tube. The cephalothorax bears the eyes, mouthparts and legs, and the respiratory openings, reproductive and digestive systems and spinnerets are attached to the abdomen.
Most spiders produce silk from spinnerets located in its abdomen. This silk can be used for several purposes, such as spinning webs, catching and wrapping up its prey and lowering itself to the ground. Silk is also used as part of reproduction. REF6
Reproduction:
Once a male spider reaches maturity, all its energy is directed towards finding a female to mate with. As the palps or genital organs of the male spider are not connected to the testes and must first be charged with sperm. To do this, the male builds a small expanse of web, on which it deposits a drop of seminal fluid. Sperm induction then takes place, where the bulb of the palp is then inserted into the fluid which is sucked up into the bulb. The male is now ready to mate with the female.
The method of approaching the female varies with each species. If she is not ready to mate, the male may be killed or loose limbs when he reaches her. This practice can be commonly seen among orb weavers.
Males die soon after reaching maturity. Once a male reaches the female to mate he inserts the palps into the female’s epigynum. In some cases the palps are inserted one at a time to eject the sperm into the spermathecae for storage. Interestingly, each egg is fertilised as it is laid. The female is able to hold the sperm for many weeks before using it. REF 4
Young spiderlings hatch and emerge from the eggs to mature over the coming months.
 Silk
Silk glands produce the silk that the spider uses for a variety of purposes. The spinnerets are the special organs that the spider uses to extract and manipulate the silk as is it is produced from the silk glands. Silk is useful to capture prey, holding eggs in sacs, lowering the spider to the ground and many other activities. Ref 13
Many hunting spiders possess dense hair tufts called scopulae under the claws of their tarsi (feet). These scopulae allow many spiders to walk on smooth vertical surfaces, across ceilings and even window panes. Each individual scopula hair splits into thousands of tiny extensions known as end feet. These end feet increase the number of contact points of the tarsi with the surface allowing them to hold onto many different surfaces. This is similar to the adhesion forces at work in vertebrates such as skinks and geckos, which can also walk on ceilings with ease. The scopulae can be erected or laid flat by hydraulic pressure through changes in the pressure blood supply. REF7
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