Droplet Interactions with the Prickly Pear Cactus and Western Diamondback Rattlesnake of the Sonoran Desert*

The Sonoran Desert is a unique xeric climate in which bimodal (summer, winter ) seasonal storms are the primary water source for plants and animals. To be able to subsist in this harsh environment, many species have developed specialized water storage and collection tactics. In this presentation, we will discuss our work on water droplet interactions involving two icons of the American Southwest: the prickly pear cactus and western diamondback rattlesnake. In the former, we discovered that seasonal hydration and dehydration cycles lead to the formation of multilevel micro-cracks of the exterior epidermis and related transition of the surface from super-hydrophobic to super-hydrophilic. While dramatically altering how droplets spread on the cacti overall, our results suggest that this seasonal epidermis microstructure is predominantly helping to regulate water vapor transport. In the second part of the talk, we will discuss how western diamondback rattlesnakes collect and drink rain droplets. This process, which is termed rain-harvesting, involves rain droplet impact onto the snake’s dorsal body, capillary transport on the skin’s surface, body shape adjustment, and suction-aided drinking. We will discuss both micro- and macroscopic aspects of these steps.