When dry, sand pours like a liquid, but under a sudden shock, dry sand acts like a solid and can support a great amount of weight. When wet, sand acts like a solid and can be easily shaped. Water creates surface tension that holds the sand grains together. Small burrowing animals that live in scrub benefit greatly from these simple facts of physics. Sand grains spread the force from shock or pressure away from the point of contact and help prevent a burrow from caving in.
Surface tension keeps the sides of a small burrow from collapsing.
Surface tension also allows small burrowing animals, such as ants, to bring up sand in little clumps rather than grain by grain. Clay is probably a better soil for building burrows than sand is, but excavating sand is much easier for most small animals than digging a burrow in clay. And although sand is more easily displaced than clay, an animal can build and rebuild its underground chambers and runways in sand with a minimum of effort. Some of the special animals and plants we see in the scrub such as gopher tortoises, sand skinks, and wedge-leaf button snakeroot are probably there because of sand. The activities in the unit are designed to help students understand the characteristics of sand and adaptations of scrub plants and scrub animals that burrow in sand.