vertebrate predators. Defensive Defensive or protective mimicry takes place when organisms are able to avoid harmful encounters by deceiving enemies into treating them as something else. The first three such cases discussed here entail mimicry of animals protected by warning coloration: Batesian mimicry, where a harmless mimic poses as harmful. Müllerian mimicry, where two or more harmful species mutually advertise themselves as harmful. Mertensian mimicry, where a deadly mimic resembles a less harmful but lesson-teaching model. The fourth case, Vavilovian mimicry, where weeds resemble crops, involves humans as the agent of selection. Batesian In Batesian mimicry the mimic shares signals similar to the model, but does not have the attribute that makes it unprofitable to predators (e.g., unpalatability). In other words, a Batesian mimic is a sheep in wolf's clothing. It is named after Henry Walter Bates, an English naturalist whose work on butterflies in the Amazon rainforest (described in The Naturalist on the River Amazons) was pioneering in this field of study. Mimics are less likely to be found out (for example by predators) when in low proportion to their model. This phenomenon is called negative frequency dependent selection, and it applies in most forms of mimicry. Batesian mimicry can only be maintained if the harm caused to the predator by eating a model outweighs the benefit of eating a mimic. The nature of learning is weighted in favor of the mimics, for a predator that has a bad first experience with a model tends to avoid anything that looks like it for a long time, and does not re-sample soon to see whether the initial experience was a false negative. However, if mimics become more abundant than models, then the probability of a young predator having a first experience with a mimic increases. Such systems are therefore most likely to be stable where both the model and the mimic occur, and where the model is more abundant than the mimic. This is not the case in Müllerian mimicry, which is described next. There are many Batesian mimics in the order Lepidoptera. Consul fabius and Eresia eunice imitate unpalatable Heliconius butterflies such as H. ismenius. Limenitis arthemis imitate the poisonous pipevine swallowtail (Battus philenor). Several palatable moths produce ultrasonic click calls to mimic unpalatable tiger moths. Octopuses of the genus Thaumoctopus (the mimic octopus) are able to intentionally alter their body shape and coloration to resemble dangerous sea snakes