Spider web

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Template:Redirect5 Image:Spider web 20040725.jpg 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.

1 Types of spider web
2 How spiders make webs
3 How spiders use webs
4 Taking an image of a web
5 Gallery
6 External links
7 Sources

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Types of spider web

Image:Orb weaver spider web.jpg Some spiders spin funnel-shaped webs, others make sheet webs, and still others make the spiral "orb" webs which are most commonly associated with the order. These webs may be made with 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 serve to disorient and knock down flying insects, making them more vulnerable to being trapped in the web below. They may also help to protect the spider from aerial predators such as birds and wasps.

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How spiders make webs

Spiders have several spinneret glands located at the spider's 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.

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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.

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Taking an image of a web

An image of an orb web may be taken on paper by spraying it gently with any dark-coloured liquid, and then placing the paper intended for the impression behind the web, and drawing it gently towards you. The idea that an impression might be produced in this manner was suggested by observing the dew on the web in the morning. Alternatively, 'misting' the web with spray paint and then capturing the web on a contrasting sheet will produce satisfactory results.

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