Monday, December 31, 2007

Spider and the Relative

All spider are carnivorous and they belong to the Arachnida class which differ from other insects most noticeably by having zero to eight eyes (some are eyeless), four pairs of jointed legs and specialized mouthparts known as mandibles or chelicerae which bear either pincers or fangs, and are use to inject poison into their prey.


Other characteristic of spiders is their ability to produce silk. They are the only members of the Arachnida (which also includes scorpions, harvestmen, mites, ticks and some small groups found only in the tropics) that produce silk. This is manufactured in liquid from six short tubes, the spinnerets, at the rear end of the abdomen.


Use of Silk

All spiders produce silk, but only some construct webs to catch prey. The web itself I sa masterpiece of weaving; different species construct different styles of webs, each of which is carefully positioned and crated to catch flying insects. The vibrations set up by a struggling insect alerts the spider and the prey is either then killed and eaten or wrapped in silk to immobilize it for later consumption.


Spider's Role in Ecosystems

Spiders are our allies in the battle against insect pests. They are all active hunters and prey on a wide range of invertebrates, many of which cause considerable agricultural losses as well as human suffering. Once a spider has overcome its prey, it kills it by injecting a poisonous substance and the sucks up the juices from the body. A spider abdomen is soft and can easily expand to cope with a large meal; female spiders, in particular are capable of absorbing enormous quantities of food within a short time. This quality makes them important regulators of insects, and they are therefore being increasingly employed in human effort to control insect pests.

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