Real facts of the SPIDER

Spiders are predatory invertebrate animals with two body segments, eight legs, no chewing mouth parts and no wings. They are classified in the order Araneae, one of several orders within the larger class of arachnids, a group which also contains scorpions, whip scorpions, mites, ticks, and opiliones (harvestmen). The study of spiders is known as arachnology.

All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen. Many species use it to trap insects in webs, although there are many species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications.

All spiders except those in the families Uloboridae and Holarchaeidae, and in the suborder Mesothelae) (together about 350 species) can inject venom to protect themselves or to kill and liquefy prey. Only up to 200 species, however, have bites that can pose health problems to humans. Many larger species' bites may be painful, but will not produce lasting health concerns.

Most spiders are unlikely to bite humans because they do not identify humans as prey.
Spiders reproduce by means of eggs, which are packed into silk bundles called egg sacs. Spiders often use elaborate mating rituals (especially the visually advanced jumping spiders) to allow conspecifics to identify each other and to allow the male to approach and inseminate the female without triggering a predatory response. If the approach signals are exchanged correctly, the male spider must (in most cases) make a timely departure after mating to escape before the female's normal predatory instincts return.

Sperm transmission from male to female occurs indirectly. When a male is ready to mate, he spins a web pad upon which he discharges his seminal fluid. He then dips his pedipalps (also known as palpi), the small, leg-like appendages on the front of his cephalothorax, into the seminal fluid, picking it up by capillary attraction. Mature male spiders have swollen bulbs on the end of their palps for this purpose, and this is a useful way to identify the sex of a spider in the field. With his palps thus charged he goes off in search of a female. Copulation occurs when the male inserts one or both palps into the female's genital opening, known as the epigyne. He transfers his seminal fluid into the female by expanding the sinuses in his palp. Once the sperm is inside her, she stores it in a chamber and only uses it during the egg-laying process, when the eggs comes into contact with the male sperm for the first time and are fertilized; this may be why the vivipary has never evolved in spiders.

Very unusual behaviour is seen in spiders of the genus Tidarren: the male amputates one of his palps before maturation and enters his adult life with one palp only. The palpi constitute 20% of the body mass of males of this species, and since this weight greatly impedes its movement, by detaching one of the two he gains increased mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male.

reference: http://en.wikipedia.org/wiki/Spider

done by zhan quan