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Spider

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== Gallery ==
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File:wspider.jpg|Water spider<br />  (''Argyroneta Aquatica'')<br />Family: [[Cybaeidae]]
Image:Yellow sac spider.jpg|[[Yellow Sac Spider]]<br />Family: [[Miturgidae]]
Image:Yellow sac spider.jpg|[[Yellow Sac Spider]]<br />Family: [[Miturgidae]]
Image:Black widow.jpg|[[Black widow]]<br />Family: [[Theridiidae]]
Image:Black widow.jpg|[[Black widow]]<br />Family: [[Theridiidae]]

Revision as of 01:03, 11 January 2010

Spider
Big spider.jpg
Scientific Classification
Family

Spiders are a member of the phylum Arthropoda. Every spider has 4 pairs of walking legs, a cephalothorax, and a opisthosoma. Many people think of spiders as scary monsters but they are actually one of the best regulators for insects and other small organisms. Most spiders are small, inconspicuous arthropods which are harmless to humans.[1]

Contents

Anatomy

Spider anatomy:
(1) four pairs of legs
(2) cephalothorax
(3) opisthosoma

Spiders only have two body segments as opposed to insects who have three. The common spider's head and thorax are fused together to create a cephalothorax. The other body segment is the abdomen. These two body segments are connected with a small waist called the pedicle or the pregenital somite. This waist allows the spider to direct the abdomen in every direction. The waist is the very last segment of the cephalothorax but it is normally lost in most of the other organisms in the class Arachnida [2].

Some tarantulas have glands that produce spider silk in their feet rather than in their abdomen. [3]


Reproduction

unidentified spider egg sac

Female spiders use eggs to reproduce, which are stored in silk bundles called egg sacs. Spiders often have very intricate mating rituals to let other organisms of the same species identify each other and let the male spider to come upon the female and impregnate it without activating their predatory response. If the mating dance is preformed correctly then after the male finishes his part in this process he will scurry out of sight before the female's normal predatory instincts return.

Spiders do not fertilize the eggs right at the moment of mating. The female actually saves the sperm for fertilization after she lays her eggs. The male spider uses a very unique process to give the female his sperm. When a male is ready to mate, he spins a web on which he ejaculates his seminal fluid. After this, he then will dip his pedipalps, or his palpi, which are small, leg-like organs on the front of his cephalothorax, into the seminal fluid. A very easy way to identify if a spider is a male or a female is by looking at the ends of their palps to see if they have swollen bulbs on them or not. The male spiders have these swollen bulbs which help in the purpose of mating. Once he has his palps coated in his seminal fluid, he goes off in search of a female. The exact time when sexual intercourse occurs is when the male inserts one or both of his palps into the female's genital opening, which is also known as the epigyne. The seminal fluid is transfered to the female spider by flaring the sinuses in his palp. The female spider then stores the sperm in a chamber in its body and only uses it during the egg-laying process.[4]

Ecology

A spider web.

All spiders are predatory but not all spiders use the same techniques. For instance, the crab spider hides in flowers and leaves so it would be more likely to capture a bee or a butterfly while a web-building spider would be less likely to capture a caterpillar. Families normally tend to capture the same type of prey based upon their capture methods which are often called guilds.[5]

Molting

An empty carcass of a spider

All spiders have an exoskeleton which they use for protection against predators. The exoskeleton does not grow or stretch so the spider needs some way to keep growing but still keep the protection of an exoskeleton. Spiders do this by molting. As the spider's body acquires nutrients a new cuticle inside the original skeleton begins to form. When the spider feels like it is the right time, it crawls out of its old skeleton which allows the soft new cuticle to expand and harden. Spiders also can stop eating for a couple of days (depending on how big the spider is) before molting.

Spider Webs

Spider webs have been described as sheet, funnel, tube, reticular and orb webs. Spiders can use their webs for protection, communication, and protecting egg masses as well as for catching prey (Williams, p.123). One aquatic spider builds a spider web tent under water that catches air to breathe. Young spiders build webs like their parents without practice or learning, apparently receiving the patterns genetically.

Evolutionists speculate whether orb webs developed once or twice, since they presume that the development is from irregular webs to regular webs. Some admit that irregular webs are not less complex to build than advanced webs, and so tracing evolution that way may not be helpful. Some also warn that people must be careful not to presume adaptation without testing to see if spiders adapt webs under evolutionary pressures. It has been found that tracing development of spiders by comparing webs means that development by anatomy must be ignored, which seems to imply that web design and anatomy may not be closely linked. It is difficult to imagine how trial and error adaptation would provide the engineering talent that spiders show.

Spiders are also interesting to creationists because they are obviously almost all predators. Did predation develop after the fall of man? or have spiders always been more or less like they are now?

Spiders and Evolution

Evolutionists believe that some of the earliest specimens of spiders evolved around 300 million years ago. However, even specimens supposed to be 300 million years already show fully-formed signs of web capability.[6]

Gallery

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Related References

  • Spiders - Wikipedia
  • Spider Ecology - Earthlife
  • Spiders by John A. Jackman, Professor and Extension Entomologist. The Texas A&M University System
  • Spider Webs, by Emmett Williams. CRSQ 25(3):123-124. December 1988.

See Also

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