“Really, what is there to be afraid of when it rains?” This iconic line from an advertisement is a metaphor encouraging people to be hopeful. But this line would actually be a factual statement if we applied it to small animals in nature! Many organisms are naturally not “afraid” of the rain as they have different structures or mechanisms that allow them to remain dry, even in heavy rain.
The Skin of a Lizard
A lizard can stay dry for long periods of time because its skin has a layer of keratin filled with minuscule spinules on the surface. When air fills the spaces between these spinules, the adhesion between the lizard’s body surface and water will be slightly lower than the water’s cohesion . Therefore, when rainwater comes into contact with the lizard’s body, it beads up into globules (or water droplets), which fall off rather than soak into the skin. At the same time, the skin surface also gets washed clean by these water droplets, killing two birds with one stone! With dry and clean skin, lizards are significantly less at risk of fungal infections.
The Scales of a Butterfly
The wings of most butterflies possess strong hydrophobic capabilities to prevent water from sticking and causing them to be unable to fly normally. The key to these capabilities lies in the wings being composed of highly hydrophobic substances such as chitin and fats, and being covered with thousands of tiny overlapping scales (Click here to know more). These scales not only form the colours and patterns of the wings, but the multitude of raised and lowered ridges from the tiny scales on the wings’ surface effectively trap air, enhancing hydrophobic efficiency by reducing their adhesion with water. However, the scales on a butterfly’s wings do not regrow, so once the scales fall off, the exposed area will lose its hydrophobic capabilities!
The Feathers of a Bird
A bird must always stay dry as wet feathers not only affect its ability to fly, they may also lose their insulating properties, potentially endangering its life. Biologists have observed how birds spread preen oil secreted from the uropygial gland on their backs evenly over their feathers. Previously, it was commonly believed that a bird’s hydrophobic capabilities came from its long-term care of this preen oil coating. However, research has since proven that a bird’s feathers are still hydrophobic even without the preen oil layer. Latest research indicates that the key to a bird’s hydrophobic capabilities lies in its feathers’ barbules, which extend from the rachis and interlock with each other. These barbules can effectively guide water towards the outer edges of the feathers, preventing water from penetrating the rachis and into the inner layers, thus bringing about good hydrophobic efficiency. In waterfowl, these barbules are longer and denser, providing better waterproofing.
