Water Absorbed From Humid Air

Biological Strategy

Tropical dog tick

AskNature Team

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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 mouths of ticks absorb water vapor from the atmosphere by secreting a hydrophilic solution.

“The ability to absorb water vapor from the atmosphere enables ticks to survive without drinking water for many months. The tick rehydrates using a three-stage process. First, it uses its foremost pair of legs to detect microregions of high humidity, such as those surrounding water droplets. Once a suitable water source is detected, the tick secretes a hydrophilic solution from its mouth. Once it is saturated, the tick draws the now hydrated secretion back into its mouth. The secretion is a hygroscopic salt solution. Once ejected from the mouth, the solution dries at low ambient humidities, leaving a crystalline substance behind. When the humidity increases, the hydrophilic crystalline substance dissolves and is swallowed back into the body of the tick. The allows exophilic ticks to absorb water vapor from close to saturation down to 43% relative humidity. Mites and soil-dwelling arachnids use a similar mechanism to absorb water vapor. This strategy might inspire innovation in the development of desiccants, building envelope design, and HVAC engineering.” (Biomimicry Guild unpublished report)

Close-up of the mouth parts of the brown dog tick showing secretion. When humidity rises above 41%, the hydrophilic secretion absorbs the moisture and is drawn back into the tick.

“The salivary s are the organs of osmoregulation in ticks and, as such, are critical to the biological success of ticks both during the extended period off the host and also during the feeding period on the host. Absorption of water vapour from unsaturated air into hygroscopic fluid produced by the salivary glands permit the tick to remain hydrated and viable during the many months between blood-meals. When feeding, the tick is able to return about 70% of the fluid and ion content of the blood-meal into the host by salivation into the feeding site. This saliva also contains many bioactive and lipid components that aid acquisition of the blood-meal. The salivary glands are the site of pathogen development and the saliva the route of transmission. The importance of the multifunctional salivary glands to tick survival and vector competency makes the glands a potential target for intervention.” (Bowman and Sauer 2004:S67)