Harmless animals that bluff their way to safety by dressing as poison
Henry Walter Bates spent over a decade collecting butterflies along the Amazon and found some he could not tell apart by their wings, even though closer study showed they were not close relatives. His explanation, read to London's Linnean Society in 1861, was that the tasty ones were wearing the costume of the toxic ones.
Bates had gone to the rainforest with Alfred Russel Wallace in 1848 and stayed long after Wallace went home. He noticed that some brightly patterned butterflies flapped lazily, as if daring birds to try them. His reasoning was that they tasted foul and predators knew it, so an edible species that copied their colours without the poison would be spared too. Coming soon after Darwin's Origin of Species, the idea offered a neat natural explanation and drew fire from critics of evolution.
The trick is a kind of parasitism on honesty. Poisonous animals advertise with vivid warning patterns, and brighter signals tend to mean nastier toxins. A mimic reaps the protection without paying to make any poison. Yet it only works while mimics stay relatively rare. If predators too often eat a harmless lookalike, they learn the pattern is a bluff and start attacking the genuine article. Where the model species is plentiful, sloppy copies still pass; where it is scarce, only near-perfect imitations survive.
Imperfection is common and puzzling. One fly that impersonates wasps lacks their long dark antennae, so it waves its front legs above its head instead. Experiments with the harmless scarlet kingsnake and the venomous coral snake it resembles found predators were fooled by the proportions of colours, not the order of the rings. Other possible explanations are that a rough copy of several models beats a perfect copy of one, or that predators simply judge differently from human eyes.
The deception is not only visual. Tiger moths click ultrasonic warnings to bats, and some edible moths broadcast similar sounds. Weakly electric fish may fake the signals of strongly electric ones. At least 22 species of passionflower sport dark dots that may pass for ants to deter grazers. The contrast case is Müllerian mimicry, where several genuinely dangerous species, like wasps and bees, converge on one shared warning.
Source: Batesian mimicry
