JAMIE BARRETT
A spider’s exoskeleton - a hard yet flexible armour made of chitin - doesn’t grow along with the arachnid. Up to a dozen times in the spider’s life, this covering is disposed of to allow for growth. After recyclable nutrients have been absorbed, a new exoskeleton is constructed and the spider pushes out of its old exoskeleton, completing the moulting process. Although the moulted skin is now of no use to the land-dwelling organism, it has certain properties that are perfect for countering a threat to sea life.
A decade after the Deepwater Horizon oil spill in 2010, the environmental effects are still being felt. In June 2017, Craig McClain and his colleagues at the Louisiana Universities Marine Consortium surveyed the Gulf of Mexico and found that species like sea cucumbers, sponges, and giant isopods had disappeared from the site. Some creatures, such as the Atlantic deep sea red crab and Nematocarcinus red shrimp, were found in large numbers, as they were attracted by the decomposition products of hydrocarbons in the oil, but the overall biodiversity of the area had plummeted.
Efforts to clean up oil spills typically use synthetic materials that resemble plastics, but these can be toxic to marine organisms and cause ocean pollution. Wool, feathers, and human hair are used as alternatives, but soak up water and sink before they have the chance to absorb much oil. The biopolymer chitin, which makes up the exoskeletons of crustaceans as well as spiders, is another natural alternative, as its molecular structure soaks up oil.
Tomasz Machałowski at Poznan University of Technology in Poland noticed that spider skins also have very strong water-repelling properties, which would help them avoid sinking by repelling water while still attracting oil. He wondered if this would make the skin effective oil sponge - particularly that of Peru purple tarantulas, which moult many times during their lives.
Machałowski and his colleagues put 100 milligrams of shed tarantula skin from this genus into a dish containing 2 grams of crude oil floating on 60 milliliters of seawater. The tarantula skin had captured nearly 13 times its own weight of oil after 2 minutes while absorbing very little water. The team concluded that the tarantula skin’s brush-like hairs trap the oil, which is then held in the chitin by the irregular arrangement of the hairs.
As oil enters the exoskeleton, it first begins to seep into tubes in the structure of chitin. Normally, when certain liquids like oil or water come into contact with a surface, forces of adhesion cause a small amount of the fluid to stick to the surface, above the level of the liquid. However, since the tubes in chitin are so thin, these adhesive forces are strong enough to draw more of the liquid up, allowing more to come into contact with the tube’s surface, so more liquid is drawn up, and so on until the tube is full. This process - known as capillary action - is also what causes water to seep through a paper towel, and liquid wax to be drawn up the wick of a candle.
The secret superpower of capillary action, combined with its water-repelling properties, means that tarantula skins could be very effective at cleaning up oil spills and decontaminating wastewater from industry. Given that there are about 190,000 spider breeders worldwide, Machałowski and his colleagues estimate that nearly 5 million shed spider skins could be harvested every year, although scaling this up may need more work.
Since the skins can be cleaned and reused (albeit with a slightly lower effectiveness), given time, this idea could prove a game changer for oil spills of the past and future. If there are found to be issues with scaling the process up, new materials could be developed that are inspired by the mechanism of capillary action and the structure of the exoskeletons.
Bibliography
New Scientist (2019). Marine life is still struggling after the Deepwater Horizon oil spill. Available at: https://www.newscientist.com/article/2214384-marine-life-is-still-struggling-after-the-deepwater-horizon-oil-spill/ (Accessed: 21 May 2020)
New Scientist (2020). Millions of hairy tarantula skins could be used to mop up oil spills. Available at: https://www.newscientist.com/article/2233478-millions-of-hairy-tarantula-skins-could-be-used-to-mop-up-oil-spills/ (Accessed: 21 May 2020)
Terminix (2020). Why Do Spiders Molt? Available at: https://www.terminix.com/blog/bug-facts/why-do-spiders-molt/ (Accessed: 21 May 2020)
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