Web Continuously Collects Water From Air

Biological Strategy

AskNature Team

Image: Pixabay / CC BY - Creative Commons Attribution alone

Capture, Absorb, or Filter Liquids

The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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Arachnids

Class Arachnida (“spider”): Spiders, mites, ticks, scorpions

Arachnids get a bad reputation, but they play an important role in the ecosystem by controlling insect populations. Almost half of the species in the class are spiders, and most live in terrestrial environments. Unlike insects, most arachnids have two body sections: the cephalothorax, which is the head and thorax fused together, and the abdomen. Mites and ticks, on the other hand, have only one body section that is relatively flat. This body shape comes in handy for the species that are parasitic, because it makes it harder for their hosts to bite or scratch them off.

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The structure of special silk from cribellate spiders continuously pulls and transports water from the air.

As air temperatures drop, water vapor in the air collects on certain surfaces, such as grass and spider webs. Not all materials do this, for example human hair absorbs water rather than letting it collect on the surface.

The webs of certain spiders, such as cribellate spiders, are particularly good at collecting water from the air. Cribellate spiders use a comb-like structure on their legs to puff up their silk into a ball-like tangle. They then weave webs that alternate these tangles with straight, smooth, thin sections of silk (threads), making a sort of beaded necklace structure that alternates the tangles separated by threads.

Water vapor condenses on all parts of the web, but it doesn’t stay equally spread throughout. Instead, once it condenses the water quickly starts to move, migrating from the thin threads towards the tangles. This happens because the tangled parts of the web have more area for the water to stick to, which ends up pulling the water from the threads, which are thinner and have less area for water to stick to. The curved shape of the tangles also helps channel water. The result is that water collects and gets stored in the tangles, creating larger and larger water drops. This movement of the water also creates new, exposed, relatively dry silk along the threads again, to which more water vapor from the air collects, in a continuous process.

The result is that these spider web structures can capture, transport, and store a large amount of water from the air. These structures, and how they work, could provide inspiration for creating new water-harvesting devices, especially in areas with low rainfall.