Birds learn to discriminate after one exposure. Some edible, nontoxic insects take advantage of aposematic coloration in other species, and mimic a toxic insect. The mimics may look exactly like it as in the case of the monarch and the vicroy butterfly which as adults are difficult to distinguish. Syphid flies mimic wasps. Spines can be laced with a toxin.
Some moths look like rotting leaves with fungus spots and the general color of a dead leaf.
Sometimes they may even have apparent feeding damages. Frequently they will have countershading to break up body outline. Crypsis works well and is very widespread. In England normally trees are covered with epiphytic lichens and mosses and are a mottled white and black or brown coloration. The peppered moth is white and black with irregular splotches and is very difficult to spot on trees covered with lichens.