Some animals hide by smell or sound, not only by colour
Trained dogs and meerkats, both of which hunt by scent, struggle to find puff adders. The snake ambushes its meals and must stay hidden from its own enemies too, so it seems to mask its odour. Hiding in plain sight, which biologists call crypsis, can work on the nose and ears as well as the eyes.
Crypsis covers any way a plant or animal avoids being detected, whether it is a predator creeping up or prey keeping out of sight. Camouflage is the obvious method, but living underground or coming out only at night serve the same purpose. Because hunters evolve sharper senses as their quarry gets better at hiding, the two sides can drive each other in a long evolutionary arms race.
Visual tricks are the most varied. Some animals match the colour and texture of their surroundings, others break up their outline with bold patches, and some, like the tawny dragon lizard, pass for rocks, twigs or even bird droppings. Ermine and snowshoe hares change coat with the seasons, while chameleons and squid shift colour in moments using pigment cells in the skin. Decorator crabs go further, gluing bits of plant, stone or shell onto their backs, sometimes choosing stinging anemones for extra protection.
A light belly under a darker back, known as countershading, is common both at sea and on land. The American artist Abbott Handerson Thayer explained it in 1896: the gradient cancels out shadows so a rounded body looks flat, the reverse of a painter's shading. Squid can go further, glowing from below to match the bright water overhead.
Scent and sound offer more hiding places. Many insects and spiders pass as ants, and the large blue butterfly's caterpillar even gets ants to feed it. Moths once seemed to confuse bats with phantom echoes, but later work found their clicks either warn bats that they taste bad or jam the bats' sonar by interfering with returning echoes.
Source: Crypsis
