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When you have legs, scampering across a body of water is certainly not most creatures’ first choice for a quick getaway. The aqueous nature of water means that it is easily distorted when any force is applied. However, some animals have evolved specialized mechanisms that use this facet of water’s character to their advantage. This phenomenon, known as surface tension, is “the force created when water molecules cling together,” according to AAAS (Pennisi). Smaller creatures that have honed this ability include water striders, a type of insect, fishing spiders, and pygmy geckos. The skin of the pygmy gecko and the waxy hairs on the legs of the arachnid are water-repellent, enabling greater stability and flotation capability. Of the creatures that can remain atop of water, these animals are known as “gliders” because their weight is too little a force to overcome the water’s surface tension (Bates).
If we take a closer look at the water striders, slow-motion video has shown that these insects create swirls by performing a vigorous rowing motion along the water’s surface that propel them forward. They can even jump up off of water and land without breaking its seal (Pennisi). Fishing Spiders row in a similar manner to that of the water striders when unhurried, however when in predator mode, they’re able to increase their speed by “galloping.” This style of locomotion is described as a sort of bounce by Robert Suter of Vassar College; “They take their first, second, and third pairs of legs and push down and backwards, and that wafts them into the air. They’re airborne for a few centimeters and then they land and push backwards again with the same legs.” These bug-like creatures essentially treat the water like land, with the arachnids feeding on insects they detect through the vibrations their prey makes in the water (Bates).
Larger creatures don’t quite have the luxury of being able to rest atop water like those previously described. MIT’s Bush elucidates that as opposed to remaining at standstill, large animals, “must be in a constant state of motion.” They fall into the category of water-walkers known as “slappers,” creatures whose weight is too great to be supported by the surface tension of the water. These include Basilisk Lizards and Western Grebes (Bates). The former, however, is unique. While waterfowl may generate substantial lift from their wings, and smaller-bodied lizards often weigh very little, Basilisk Lizards, can run over water with only their hind legs providing the necessary lift and thrust. They additionally have a large range in size, weighing from two grams as hatchlings to up to 200 grams as full-grown adults. In a study conducted by Hsieh and Lauder on the force generated by Basilisk Lizards, each stride was divided into three distinct phases: the slap, stroke, and recovery. The kinematics of the lizards’ foot are depicted as follows, “During the stroke phases, the foot sweeps primarily backwards and medially, ultimately shedding a vortex ring as it transitions into the recovery phase. The recovery phase completes a stride cycle, returning the foot to the start of slap.” This spectacle of a movement is broken down in the figure.
Though humans have much too great a mass to walk on water (other than Jesus of course), we are still able to marvel at the creatures that can. Using a variety of styles—from a spider’s bouncy gallop or insect’s rowboat paddle, to a lizard’s quick scamper—animals have discovered and capitalized upon water’s limited surface tension as a means of survival.
Works Cited
Bates, Mary. “Amazing Animals That Walk on Water.” National Geographic Society, 19 June 2014,
Hsieh, S. Tonia & George V. Lauder. “Running on water: Three-dimensional force generation by basilisk
lizards.” Proceedings of the national Academy of Sciences of the United States of America, vol. 101, no. 48, 30 Nov. 2004, pp. 16784-16788, www.pnas.org/content/pnas/101/48/16784.full.pdf.
Pennisi, Elizabeth. “The Secret to Walking on Water.” American Association for the Advancement of
Science, 13 Mar. 2014, www.sciencemag.org/news/2014/03/secret-walking-water.
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