SPIDERS
The word spider came from an Old English verb spinnan.Spinnan means tospin.People in Eroupe see spiders with distaste, in African and in American culturesspiders are respected. Spiders are the most abundant and distinctive of all earthly predators. Most of thetime they are not dangerous to us, spiders eat almost always insects and are found inplaces from the Tundras all the way to the low forrests They play abig job in taking careof the insect population, even the ones that can give us diseases. Distinctive CharacteristicsEven though insects and spiders belong to the group called, Arthopoda, they lookso different from each other so they are put into different classes. The Insects and theArachnids. Scientists think that these two classes split up thousands of years ago.
External Anatomy Spiders come in different sizes, some of them are only 0.1 centimeter long,andsome of the are more than 4 inches long. They have two body parts and eight legs. Thespiders head and thorax are one body part. The thorax is the chest area of a spider. Theabdomen or the stomache is the second body part Each leg has seven sections, and onthe tips of many spiders legs are two tiny claws. Spiders that make a web use these clawsand their notched hairs, to walk on their webs without sticking to them.
Like insects, spiders have a body shell called an exoskeleton. This shell covers thebody and the legs and keeps the spider from drying out. Much like our skin is to us. Andto support the spider like our bones support us. Spiders even have a skelton inside calledthe internal skeleton. This is where the muscles attach.
Unlike insects, spiders dont have antennaes. They do have two things near theirmouths these are called pedipalps. They are used by spiders to handle their food. Thepalps of a baby male spider look like boxing gloves. When they grow up the palps areused for breeding.
Sensory OrgansSpiders have eight eyes in two groups and some spiders can see images. Otherscant and they have to rely on feel like those on webs. Web weaving spiders eat, breed,and lay their eggs from silk threads.
The main part of a spiders senses are two types of hair. The tiny ones have nerves.
When these hairs are bent they send information to the brain and may cause it to runaway or get ready to attack. They also sense touch, vibration and air flow.
The second type of hair are the even tinier one these keep an eye out for pressurechanges in the air.
Curculation and LocomotionSpiders have an open circulatory system this means that they have no bloodvessels or arteries. Instead, the blood oozes between the spiders flesh, and collects inlittle pockets on the underside of the body.
A good circulation is very important to the spiders legs. When spiders dont getenough water, their legs fold up and they cant move them.
RespirationSpiders have different kind of respitory systems. Some have a tubular tracheae,some have book lungs, and others have both. They first spiders to live had one or twopairpairs of book lungs. The spiders now days have one pair of book lungs and a pair oftubular tracheae.
DigestionSpiders are th only animal to digest their food on the out side of their bodies. Thegut of the spider is behind its stomach, and part of it goes into the front legs. This lets thespiders to live for days without eating.
VenomAlmost all spiders have venom glands. Most spider venoms are not harmful to us,but the black black widow and the brown recluse spiders will poisen us.
Spider SilkWhat makes a spider a spider? They can spin a web. All spiders, even baby ones,have silk glands and spinning organs called spinnerets. The silk glands push the web outand the spinnerets weave the web.
Works CitedFirst reference. The Comptons Interactive Enclopedia CD ROM.
Additional reference.The Discovery Channel On-Line on the internet.
