Most people see only a few of the millions of insects around them. While most insects and spiders are small and difficult to see, many are longer than an inch (2.5 cm) but blend with their background. Others appear to predators as inedible materials such as bird droppings, leaves, thorns, and stones. The ways in which these animals derive benefits from their coloration are usually exquisitely enmeshed with their behaviors, and these interactions are the topic of this essay. Being nearly invisible allows an animal to escape predators or to sneak up on prey without warning it of an impending attack. There are many ways to blend into a background: crypsis and color matching, camouflage, distruptive coloration.
Color Matching
When an animal's coloration matches its background, the animal blends into the scenery and becomes hard to see.
- Young Chinese mantids (Tenodera sinensis) are the same color green as the grass and vegetation they wander across while hunting. As the grasses begin to turn brown in the autumn, the adult mantids develop brown stripes, becoming brown and green. The ability to match changes in the background both enables the mantid to approach prey closely and escape detection by birds looking for food. Many grasshoppers, katydids, caterpillrs, aphids, leafhoppers use this color matching strategy to blend into their background.
- Some tropical mantids specialize in taking on the same color as the flowers they hunt on use this same behavior. These mantids also may develop flat plates on their head, limbs, thorax, and abdomen which enhance their similarity to the petals of these flowers. To the casual observer, the mantid is practically invisible.
- Crab spiders that forage on both vegetation and flowers have the ability to change their color back and forth between green and the flower color. This change in color may take as little as a few minutes in some species, or will not occur until the spider's next molt in others. It is not unusual to see spiders of two or three different colors on different plants in the same area. Sometimes the spider poses on a plant as if it were a flower and capture unwary pollinators as they attempt to gather pollen and nectar. The usual colors are green, white, and tellow. But some crab spiders can become pink to match their chosen flowers. Even if they do not match the flower color, white spiders are almost invisible to foraging insects on yellow flowers – yet, yellow spiders show up on white flowers.
Crypsis
Crypsis takes color matching a step farther and the insect appears to be something it is not.
- Some caterpillars, such as that of the oak beauty moth (Bistron strataria, pictured), resemble twigs when resting. It is almost startling to see a "twig" assume the typical inchworm loop when it decides to move on. When resting, this caterpillar enhances the "twig" effect by tucking its head down and bringing its front legs forward to its chin. In this way, the anterior end of the caterpillar looks like a bud at the end of a short twig.
- Many butterflies and moths have their wings patterned to look like leaves, lichen-covered tree bark, or stones. In many cases, the wings of these insects will have irregular notches and projections that further enhance the deception. Noctuid, geometrid, and sphinx moths are examples of this type of crypsis.
- The black and white stripes of the zebra jumping spider stand out when one forages on plants. but against a rock, these spiders are virtually invisible.
- Viceroy butterfly (Limenitis archippus) caterpillars, bird dropping moths (Ponometia erastrioides) caterpillars and the Australian bird-dropping spiders (Celaenia excavata) resemble bird droppings. Thus, although they are readily seen, their pattern matching renders them part of the background.
- Several leaf-hopper species (some of which forage on thorny plants) have spines on their backs and triangular bodies that resemble thorns in shape and color. It takes a discerning eye to notice the slight lifting of the insect's bodies as they such nutrients out of the plant stems they feed on. Some of these feed on non-thorny plants, but the deception is so good that most possible preadators continue to ignore them.
- The larve of froghoppers (Clasirptora sp.) pump and eliminate large quantities of sap from their food plants. they then kick the sap into a foam resembling spit or the discharge from an injured plant stem. these larvae are commonly called spittle bugs and are overlooked by most predators. Deception is not the funciton of this behavior for many birds and insects prefer to keep their heads and walking legs free of the somewhat slimy spittle. Thus, whether rejection is because of deception (crypsis) or mechanical reasons, the insect remains hidden and for the most part unmolested.
Camouflage
Camouflage is similar to color matching in that the animal does not display a detailed copy an inedible object. It differs from color matching in that the colors and patterns displayed may differ from the background.
The dots and lines on a painted lady butterfly's closed wings, the bright yellow and black stripes of a golden garden spider, and the bright dots on a golden orb weaver seen in patchy sunshine, and the cecropia moth's closed wings in shade camouflage these animals from unwelcome eyes. None of these color patterns resembles the background the insect or spider is displayed against, but the overall effect is to render the insect or spider invisible.
Disruptive Coloration
Although camouflage approaches this mode of hiding the identity of an animal, disruptive coloration is designed to break up the outline of an animal that would otherwise be quite visible. The saddle of a prominent moth caterpillar disrupts its elongate shape into three seemingly unrelated portions: two pale separated by one dark. Striped along the sides of other caterpillars – even when contrasting with the background color, look like a darker or lighter region of the stem, twig, or leaves the caterpillar is resting on.
Coloration of quite different types can also provide protection for animals. Some are brightly colored as advertisement that they have dangerous spines, are poisonous, or are highly aggressive. Many innocuous animals copy those that are brightly colored and obtain relief from predation when experienced hunters think the innocuous animal is dangerous. These features will be covered in in upcoming articles.
References
Animal Camouflage: Current Issues and New Perspectives. Stevens, M. and Merilaita, S. Phil. Trans. R. Soc. B 27 February 2009 vol. 364 no. 1516 423-427.
Disruptive Contrast in Animal Camouflage. Stevens, M. et al. Proc. R. Soc. B 7 October 2006 vol.
273 no. 1600 2433-2438.
Disruptive Coloration Provides Camouflage Independent of Background Matching. Schaefer, H.M. and Stobbe, N. Proc. R. Soc. B 7 October 2006 vol. 273 no. 1600 2427-2432
Albert Burchsted - Ph.D. in animal behavior, field biologist, and photographer. Al leads nature study walks and is an environmental consult in SE ...
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