Quirks & Quarks

Rattlesnakes have skin that's sticky for raindrops so they can sip from their scales

Nano structures on their scales help the snakes capture scarce water in their desert homes

Nano structures on their scales help the snakes capture scarce water in their desert homes

Rattlesnakes like the western diamondback can drink droplets of rain water on their backs (Sandra Keaton Leander/ASU)

Special structures integrated into the skin of rattlesnakes holds droplets of water on their skin. This allows the snakes to capture water during rare desert rainstorms, which they then sip carefully off their scales.

Snakes in the rain

Naturalists have long known that rattlesnakes sipping water from their bodies after a rainfall in the past. The snakes emerge from their dens and curl up to catch as much moisture as they can. 

In a new study, Konrad Rykaczewski, a professor of Mechanical Engineering at Arizona State University and his colleagues described how the snakes are able to keep the rainwater on their bodies. 

Rattlesnake scales as seen through an electron microscope. These channels prevent the rainwater from slipping off the snake's body. (Konrad Rykaczewski/ASU)

Most rattlesnake species live in the hot, dry climate of the American southwest and Mexico. A challenge for most of the animals that live in these regions is staying hydrated in an environment that experiences very little rain. 

Harvesting rainwater

Rattlesnakes will emerges from their dens during periods of rain, sleet and even snow. It flattens its body and forms a tight coil. When a sufficient supply of rain has fallen on the snake's body, it sips water that has collected on its scales. There are many other species of snake in these regions, but the rattlesnake is the only one known to have this ability.

Other snakes will travel to a puddle or creek to drink, but rattlesnakes tend to be stationary. Even their hunting strategy is to not move too much, preferring to let the prey come to them. 

Southwestern speckled rattlesnake (Sandra Keaton Leander/ASU)

But the question as to why the rainwater simply doesn't run off the snakes' back piqued the curiosity of Rykaczewski and his colleagues. Rykaczewski often works with bio-inspired materials, and has studied other natural materials and surfaces that tend to repel or hold water. 

Sipping the scales

The team investigated the the surface wetability and nano texture of scales of the rattlesnake and compared them to two other species of snake who do not display the rain collecting behaviour, the desert kingsnake and the sonoran gopher snake.

When water droplets were dropped on to the rattlesnake skin, the water beaded into much smaller droplets but stuck to the rattlesnake's scales. With the other snakes, the water simply slipped off. Using scanning electron microscopy, the team found rattlesnake scales have a network of nano-channels. These channels collect the water and create an adhesive effect for the droplets. Rykaczewski calls it a hydrophobic surface that holds water to the surface of the scale. The scales of the other snakes did not have such adhesive channels. 

Why rattlesnakes love a rainy day (American Chemical Society)

This mechanism explained both the coiling behaviour as well as the flattening of the body during a rain shower. This increases the surface area of the snake's skin, allowing more rainwater to collect.

The team has been considering applications for thir finding. Rykaczewski thinks it could be useful for improving fog capture in regions that experience little rainfall.