“Spider silk how sticky is too sticky?”

Modern spiders, the orb spiders, weave a variety of intricately shaped webs, but usually never get caught in it. It seems scientists have found that the silk threads that make up the web different in stickiness. The spiders travel on the non stick paths across their webs.

Orb spider's web

Orb spider's web

There is a direct correlation between the strength of a silk fiber and its stickiness.

If they made the silk threads stickier, a wriggling insect wouldn’t be able to release itself from the glue, but its struggles would ultimately break the fiber, and with it the web, ensuring its escape. If the glue is only so sticky, then the insect might be able to pull free from one capture spiral on the web, but it would then likely come into contact with the same thread again, or another and finally be too tired to struggle free. By detaching instead of breaking, a capture spiral in the web can repeatedly adhere to an insect and continue to disrupt the insect’s struggles to free itself. If the silk threads of the web were all maximumly sticky then the spider might get caught in its own web and would die.
Scientists have found that if the webs of spiders were any more sticky, they would break as they trapped insects, letting the prey escape. So a spider has to balance the stickiness of its web with how strong it is. This limits how adhesive spiders’ webs can become, forcing the creatures to evolve webs of an optimal stickiness, according to a study published in the Journal of Zoology. When tested each silk fiber on a web would release the test object it was trapping when 20 to 70% of the force required to break the fiber was applied. Seems to be a safety feature built in to thread strength and glue stickiness used to coat the threads.

Have spider webs changes over the ages?
Spiders create architecturally elegant webs by first laying down radial lines of dry silk, upon which they weave regularly spaced elastic spirals of sticky capture silk. But more than 100 million years ago, in the early Cretaceous period, spider web design changed and stickiness increased as the orb-shaped webs evolved. These araneoid orb weaving spiders seemed to have needed a better way to hold its prey.

Before then, spiders coated the spirals in their webs with puffs of dry adhesive. These dry spirals trapped insects by physically entangling around the tiny hairs known as setae on their bodies. A group of spiders living today, known as deinopoid spiders, still weave webs in this way.
During the early Cretaceous, aranoid orb weaving spiders evolved which weaved a different type of web. These spiders replaced the dry adhesive with wet droplets of glue. These are much stickier.
Maybe the stickier webs are more efficient at catching and holding prey.

Resources

Excerpts courtesy of News.bbc.co.uk/earth

Excerpts courtesy of WileyInterScience ow.ly/e8pq

Excerpts courtesy of   Jeb.biologists.org

Image courtesy of wikimedia.org/wikipedia/commons/Spider_web_with_dew_drops

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