Alright, so what was supposed to be a short note on a cool encounter I had with a sword-bearing conehead (more on this next week), has turned into a longer series on camouflage. Here we continue with disruptive camouflage (breaking up the outline of an animal’s body) before looking at mimesis (where the animal looks like some benign object in the environment).
Hiding your animal form
As with babies (see last week’s newsletter), sighted animals detect patterns of shapes and then assemble these abstracted configurations into the idea of an animal. Jumping spiders, for example, detect mosquitoes (a common prey item) by seeking out shapes that look like little stick figures consisting of a few legs attached to an abdomen. You can put the legs in pretty much any arrangement along the underside of the abdomen and the spiders will still think “Mosquito!” But flip this arrangement upside down so the legs are above the abdomen and the spiders are blind to the mosquito (source). Mosquitoes don’t go flying around upside down, but there are ways that prey can appear to be anything but the pattern a predator might use to spot them.
Prey might do this with visual patterns that disrupt the clean lines of their frame, concealing the otherwise obvious shape of the body. Sharply contrasting patterns on an animal’s body makes it tough to discern its edges. Many animals have spots or stripes on two different parts of their body. The repeated patterns create a visual bridge from one part of the body (like a wing or leg) to the trunk (as in the pickerel frog above).
Hiding the prominent shapes that define an animal’s form can also help confuse the visual system of a predator. When I think butterfly, I think wing. And it seems plausible that the Carolina wren living in my backyard spending its days hunting crickets and butterflies has developed a similar “wingy” search image for butterflies. Some butterflies (like the tortoiseshells, which includes mourning cloaks, pictured above) have an irregular contour on the trailing edge of their wings. The rough edge masks the wing’s wingy-ness (when the wings are held closed, they look more like dried leaves).
Eyes are the window to the soul, and if you’re a predator, they are also an immediate and easily detectable feature of your prey. As one of the most visually arresting and obvious features we and other animals are primed to see, hiding the obviousness of one’s eyes is another great way to hide from predators. And indeed many creatures have masks, bands, or stripes that cross over the eyes and obscure their form, as in the mask of a wood frogs (above) or the superciliary stripe on so many birds, like chipping sparrows (below).
