Spider Man's Powers Revealed In Humidity-Responsive Web Glue

Out of the 45,000 known spider species, only 7,500 of them are doing the whole web-spinning bit that we tend to associate with them. Those spiders spin webs using "capture silk," which ultimately adheres to prey passing and gives the insects a buffet to feed on. Scientists have long marveled at the arachnids' ability to weave such intricate traps. So how do they do it?

Well, their capture silk consists of an axial fiber coated with "glue droplets" at regular intervals, according to a news release. This "spider glue" is unique, in that its adhesion increases in response to humidity, researchers from the American Institute of Physics (AIP) revealed in a new study. For some species, the adhesion continues to increase up to 100 percent relative humidity (RH).  Scientists have begun exploring how this could be adapted to common Band-Aids, which are synthetic adhesives that instantly peel off in response to a higher humidity, or simply, when you sweat.

For their study, researchers explored the underlying properties of "spider's glue," and how their adhesive capabilities differed when the amount of water vapor in the air varied. The scientists specifically examined the capture threads of five diverse species of spiders.

"The habitats of these species ranged from dry to wet and humid, so we measured the adhesion as a function of humidity and used high-speed imaging to quantify the spreading rate of the spiders' glue droplets," Gaurav Amarpuri, one of the study's researchers from the University of Akron, said in the release.

In their study researchers explained that the liquid glue droplets follow the "spreading power law." This simply means thinner droplets spread more readily than thicker substances. Researchers used this to calculate the spider glue viscosity as a function of humidity.

"We discovered maximum glue adhesion at the humidity levels at which the spider usually forages," Amarpuri explained in a statement. "This is intuitive, but beautiful to observe in data." (Scroll to read more...)

When the air is warmer, it is less dense and can hold more water vapor, compared to cold winter air, for example. After analyzing spider glue peeling under a microscope, researchers concluded that its extensibility increases with humidity, according to the release. This illustrates how the spiders are able to adapt to climate change and continue hunting.  

Researchers also took a closer look at the proteins and salts present in the spider glue. They hope this will help them better understand the role of salts in controlling viscosity and adhesion.

Their findings were recently presented at The Society of Rheology's 87th Annual Meeting in Baltimore. This study may aid in the development of stickier, sweat-resistant Band-Aids, otherwise known as "smart adhesives."

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