Vulnerability And Defense
The survival of butterflies is influenced by many factors, and their populations may increase or decrease quite rapidly, and from year to year. Brilliantly colored butterflies are often toxic when eaten, so predators learn to leave them alone. Occasionally, a non-poisonous species evolves that mimics the appearance of a poisonous species, thus being less susceptible to predators. Dark colors, displayed by butterflies in cooler climates (such as alpine or arctic tundra), readily absorb sunlight so the cold-blooded insect can warm up more quickly.
Some butterflies are well camouflaged and almost undetectable among the flowers of their particular food plant. A variety of spots resembling eyes on the outer edges of the wings of certain species may startle or distract predators, drawing the point of attack of a swooping bird away from the butterfly's soft body. Some butterflies do a 180-degree turn before landing, so the eye-spots on the wings are positioned where a predator may think the head should be. Butterflies surviving bird attacks can often fly well even with a piece of wing missing.
The underpart of the wing is usually duller than the surface, so that when the butterfly assumes its resting position with wings folded above its head, it is cryptically colored, blending into the background on which it lands. Some butterflies use the club on the end of the antennae to knock small predators off their body.
The hairy spines on many caterpillars deter predators, and their colors often blend in with the leaves of their food plant. Some pupae develop hornlike appendages on the head and rear of the chrysalis, which appear to point menacingly at predators. In other cases, a chrysalis hanging from a twig may look like a dead leaf.