There are many molecules on Earth which hold water - spider silk being one of them. In nature the leaves of some plants in the desert and the backs of desert beetles are some. In particular, spider silk has an ideal mechanism for holding water. So much so, in 2010, Chinese scientists published a paper in the journal 'Nature' where they wrote about the structure of spider silk in a lot of detail. They showed that when the spider silk gets wet, rough 'bumps' begin to form on what would otherwise be the smooth side of the silk. The idea is that these changes in texture cause changes in pressure which drives the water through and into the bumps - hence this water collecting ability. This is similar to when you see water droplets on a spiders web - scientists call this phenomenon 'spindle knots' as they kind of act like collection sites. The hope is that scientists could potentially mimic the structure of spider's silk which could be used to harvest water from moisture in fog in dry regions.
