Countershading
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Image:Greyreefsharksmall.jpg
Countershading, or Thayer’s Law, is a form of camouflage. This protective coloration is characterised by darker colouring of areas exposed to light and lighter colouring of areas that are normally shaded, by which forms appear less round and less solid through inverted shading. Many marine animals employ this form of camouflage, including various species of fish, particularly sharks, and cephalopods. When seen from the top, the darker dorsal area of the animal blends into the darkness of the water below, when seen from below, the lighter ventral area blends into the sunlight from the surface.
Countershading is also used by land animals. Military camouflage sometimes uses the same principle.
Abbott Handerson Thayer was one of the first to conduct extensive research on and to write about certain aspects of protective colouration in nature. In 1892, he wrote about the function of countershading in nature, in which he accounted for the white undersides of animals. For this reason countershading is sometimes called Thayer’s Law.
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