Water Droplets on a Spider's Web on the Viterbo Airport Control Tower

November 22, 2019



Photographer: Marco Meniero
Summary Authors: Marco Meniero; Jim Foster

The spider web featured above, adorned with silver beads of dew, was captured at the 303 ft (92 m) level of the Viterbo Airport Control Tower, Italy. Once the air temperature drops to the dewpoint, water droplets will form on just about any item, whether it's woven or solid, that’s at least exposed somewhat to the sky. Though the droplets stick to the silken threads as a result of capillary action, why droplets rather than a continuous film of water forms can be partially explained by the phenomenon known as Rayleigh-Taylor instability. Of course, surface tension plays a major role in determining how liquid molecules interact with each other.

Notice that a few drops of water have funneled down toward the center of the web. These larger drops act like lenses and refract the background scene upside down (bottom photo – the sky is below the green fields and trees).