Spiders have more than one web

Why is the spider not stuck in its own web?

Part of the answer is: A spider's web is not sticky everywhere - the main threads emanating from the center and also other parts are not provided with "glue droplets". When the spider moves on the web, it specifically steps on these structures. But of course she sometimes comes into contact with the sticky intermediate threads. Two researchers have investigated why they do not stick together and become entangled in this case. William Eberhard from the Smithsonian Tropical Research Institute and Daniel Briceño from the University of Costa Rica conducted their study on two orb-web spider species: The tropical one Gasteracantha cancriformis and especially the golden silk spider Nephila clavipeswhich occurs from the USA to Argentina. It is often the subject of research because its networks are large and extremely stable.

In order to be able to look closely at the spider's legs, the researchers used special cameras and macro lenses. The spider web's adhesive effect is triggered by tiny drops of adhesive on the special catch threads. One of the researchers' cameras was therefore equipped with an integrated microscope and aimed specifically at the thin, hairy spider legs to determine how the individual drops of adhesive behave when they come into contact. In this way, the biologists were able to document in detail how the eight-legged animals handle their net.

Adhesive droplets roll off

The video footage revealed that when it hit the spider's leg, the glue would roll off the fine hairs on the spider's legs. They are apparently coated with a substance that does this, Eberhard and Briceño concluded. To test this assumption, they carefully cleaned the legs of the test spiders with chemical substances. The subsequent observations actually showed that the glue droplets did stick to the spider's legs without the non-stick coating.

The researchers conclude that the combination of fine hairs with a sophisticated coating enables the orb web spiders to move on their webs and easily handle the adhesive threads when building the structure. In principle, however, another aspect also plays a role:

In the case of the researchers' experimental spiders, the golden silk spiders, this is truly a spectacular work of art: They build with their long legs, which can span up to 15 centimeters Nephila Species the largest known wheel nets with a diameter of up to two meters. The spider silk is so tear-resistant that the webs of Nephila pilipes can even be used as fishing nets in the South Pacific. To do this, fishermen set up bamboo tubes as a frame in which the spider spins its web, which is then used to catch small fish.

Source: University of Costa Rica, Natural Sciences, doi: DOI: 10.1007 / s00114-012-0901-9

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23rd July 2018

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