A General Introduction.
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Leg of a garden spider (balsam mounted specimen). Argyopidae aranea.
The spiders are the best known members of the class Arachnida, which also includes the mites, ticks, scorpions and other scorpion-like creatures.
The bodies of all of the Arachnida have two main parts; the prosoma (or cephalothorax) and the opisthosoma (or abdomen). The prosoma bears six pairs of appendages: the chelicera (jaws), the pedipalps, and four pairs of legs. The chelicera are located forward of the mouth, and are used for holding, piercing, and the injection of poisons which paralyse the prey organism -- usually insects or other spiders.
The spiders are very diverse in size, lifestyle and adaptation. Something like 40,000 species have been described, and there remain many regions on Earth where studies of spiders have not yet been undertaken.
Spiders, like all arthropods, grow in size by a process of moulting, and a mature spider will have moulted between two and twelve times during its lifetime. Females take longer to mature than males, and undergo a larger number of moults.
A spider which is ready to moult usually finds a quiet place to hang by its claws, and by increasing the blood pressure in the prosoma, causes the old cuticle to crack in a line which runs around the prosoma above the level of the legs, and below the eyes.
The spider is then able to slowly extract its legs from the cuticle by alternately increasing and releasing its blood pressure. The thin cuticle covering the abdomen also splits and contracts, leaving only a shrivelled remnant.
The newly-emerged spider, soft and vulnerable, hangs by a thread intil its new cuticle hardens.
The series of pictures below shows the discarded cuticle, or exuviae, of a common house spider.
The above photographs were taken using a Kodak DC4800 3.1 Megapixel digital camera fitted to the eyepiece of a low-power Russian MBC2 stereo microscope.
A Newly Hatched Spiderling.
These pictures of a young spider, recently hatched from its egg, were taken using a microscope illuminated by a double electronic flash setup which is described as part of the article on electronic flash as a microscope illuminant. Click here for more details on the technique used.
The pictures show the spider suspended in a web constructed across the lower half of a small transparent plastic container, and provide an opportunity to observe the way in which the creature uses its rear legs to manipulate the thread generated by the spinnerets.