Spiders were thought to decorate their webs to stabilise them but this is not accepted any more, even though there is no consensus on the reason for the spiders’ art.
Perhaps it is just the spiders’ aesthetic sense.
image from arkinspace.com
A whole gallery of spider art is at Ark in Space.
The structures are known as web decorations but the more scientific name for one is stabilimentum. In the plural they are known as stabilimenta and the name came about because of a mistake. When first studied the decorations were believed to be used in stabilizing the web of a spider – and there you have the term stabilimentum – get it? However, this theory is generally dismissed these days – although it is obvious to one and all why early scientists may have thought this. …..
…. The truth be told, it is quite likely that the purpose and function of stabilimenta are manifold. It has been discovered that they evolved independently perhaps as many as ten times. Some spiders make their decorations purely out of their silk. Other spiders will make them from this and the remains of their egg sacs, not to mention any detritus that just happens to be close to their webs. The fact that they evolved independently does seem to point towards different functionality. ……
Some think that the web decorations afford the spider and extra edge in terms of self protection. It may make spiders appear larger, as already seen, or make them more camouflaged. It may be the reverse of camouflage – by making the spider more visible then the web itself will be seen by animals like birds that are then less likely to inadvertently damage the web, partially wrecking or even destroying the painstakingly built structure. So it could well be a kind of ‘stop sign’ to other animals. …… One more modern idea posited is that the stabilimenta are used in order to attract more prey to the web. You have all seen insects at night flying towards lights? Ultraviolet light is often used to attract insects and then there is a sharp noise of insect flesh impacting and exploding under the influence of an electric current. It is now thought that the web decorations reflect ultraviolet light and this makes them attractive to a large number of insect species. Unwittingly they fly to their deaths.
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