Body Parts

Spiders are characterised by having two body parts, joined by a narrow waist. The first part is a fusion of the head and middle section (together called the "cephalothorax"), which bears the eyes, mouth-parts and legs and is covered with a shield-like carapace. The second part is the abdomen, containing reproductive and digestive organs, silk glands and the "spinnerets".

At the front of a spider's head are its fangs - hollow, needle-like structures used to capture and kill prey, and for defence. Behind the fangs are a pair of appendages called the pedipalps, which basically act as touch receptors. Mature males bear enlarged sex organs at the end of their pedipalps, which they wave at females during courtship displays. These organs are the major external difference between males and females, but females are also generally larger than males.

Spiders have four pairs of walking legs, variable in form and function but generally simple and unspecialised. In most spiders the two front pairs of legs point forwards and the two back pairs face backwards. In groups such has huntsman and crab spiders, the legs are turned sideways so that the "knees" point towards the back of the body, enabling the spider to walk in very confined places such as under bark. The legs usually end in a pair of claws which may be surrounded by tufts of fine hairs that help the spider walk up vertical surfaces and upside down on ceilings. Each tuft may contain 1000 tiny individual hairs. These tufts also help some spiders walk across water.

The main external feature of the abdomen is the spinnerets - segmented finger-like appendages from which the silk is drawn. Most spiders have three pairs of spinnerets. At least six groups of Australian spiders (including humped spiders, net-casting spiders and house spiders) also have a special spinning plate called the "cribellum", just in front of the spinnerets, which is used to comb out wide ribbons of silk.