Spider web
From Wikipedia, the free encyclopedia
A spider web, spiderweb, spider's web or cobweb (from the obsolete word "coppe", meaning "spider" [1]) is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets. Not all spiders build webs to catch prey, and some do not build webs at all. The word "cobweb" is usually used for a web inside a house, where dust has gathered on the sticky silk, forming long, hanging streamers.
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[edit] Types of spider web
There are a few types of spider web found in the wild; and many spiders are classified by the webs they weave. Different types of spider webs include, but are not limited to:
- Spiral orb webs, associated primarily with the family Araneidae as well as Tetragnathidae and Uloboridae
- Tangle-webs or cobwebs, associated with the family Theridiidae
- Funnel-webs, with associations divided into primitive and modern
- Tubular webs which run up the base of trees
- Sheet webs
Several different types of silk may be used in web construction, including a "sticky" capture silk, or with "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These tangled obstacle courses serve to disorient and knock down flying insects, making them more vulnerable to being trapped on the web below. They may also help to protect the spider from predators such as birds and wasps.
[edit] How spiders make webs
Spiders have several spinneret glands located at the their abdomen which produce the silken thread. Each gland produces a thread for a special purpose. Seven different gland types have currently been identified, although each species of spider will possess only a few of these types, never all seven at once.
Normally a spider has three pairs of spinnerets, but there are spiders with just one pair or as many as four pairs of spinnerets, with each spinneret having its own function.
Webs allow a spider to catch prey without having to expend energy by running it down. Thus it is an efficient method of gathering food. However, constructing the web is in itself an energetically costly process due to the large amount of protein required, in the form of silk. In addition, after a time the silk will lose its stickiness and thus become inefficient at capturing prey. It is not uncommon for spiders to eat their own web daily to recoup some of the energy used in spinning. The silk proteins are thus 'recycled'.
Some spider silk strands are stronger than steel strands of the same thickness; the microstructure of this material is under investigation for potential applications in industry.
[edit] How spiders use webs
The spider, after spinning its web, will then wait on, or near, the web for a prey animal to become trapped. The spider can sense the impact and struggle of a prey animal by vibrations transmitted along the web lines.
Spiders do not usually adhere to their own webs. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor web movement. Spiders have to be careful to only climb on the non-sticky strands of their webs.
A spider positioned in the middle of the web makes for a highly visible prey for birds and other predators. Many day-hunting orb-web spinners reduce this risk by hiding at the edge of the web with one foot on a signal line from the hub, or by appearing to be inedible or unappetizing.
Some species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. Trapdoor spiders) or running them down in open chase (e.g. Wolf spiders). The Net-casting spider balances the two methods of running and web-spinning in its feeding habits.
This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy loss of weaving a large orb-web.
Some spiders manage to use the 'signaling snare' technique of a web without spinning a web at all. Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.
[edit] Spider webs and drugs
Administering certain drugs to spiders has an effect on the structure of the webs they build. It has been proposed by some that this could be used as a method of documenting and measuring the toxicity or the effects on motor co-ordination of various substances.[1][2]
[edit] Gallery
 Funneled spider net |
 Spider web early in the morning |
 Cobweb on a fence; an example of a sheet web |
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[edit] External links
- Spiders on drugs The supposed effects of drugs on spider web building
- Web construction in Araneus diadematus Movie of the web construction in the cross spider Araneus diadematus
- Oldest known spider web A 110 million year old web preserved in amber
[edit] References
- Ed Nieuwenhuys, The Spider Web and Thread. March 2002.
[edit] Notes
- ^ Jackson, Robert R. (1974). Effects of D-Amphetamine Sulphate and Diasepam on Thread Connection Fine Structure in a Spider's Web (PDF). North Carolina Department of Mental Health.
- ^ Noever, R., J. Cronise, and R. A. Relwani. 1995. Using spider-web patterns to determine toxicity. NASA Tech Briefs 19(4):82, Spiders on speed get weaving. New Scientist (29 April 1995). Retrieved on September 8, 2006.
