Some individual animals will die or receive damage while birds or mammals on the attack learn about the connection between colour and taste. However, if warning costs less than hiding, the animal benefits. And the advertising traits such as colours may serve other functions as well. The patterns may help mate identification within the species, for instance.
The fact that some animals are genuinely dangerous or noxious (disgusting) to eat gives the opportunity for mimicry based on warning colouration: Müllerian and Batesian mimicry.
In Müllerian mimicry, some species with warning colouration come to look like each other. English naturalist Henry Walter Bates first noticed that some distasteful butterflies resembled one another, which he wrote about in 1862. However, he did not give a good explanation; that was left to German naturalist Fritz Müller in 1878. Müller's explanation was simple: "Both species benefit from a common pattern". They share the cost of predators learning of their foul taste. Only one learning experience per predator might well be enough to deter it from eating both species.
The butterflies Bates, Wallace and Müller watched and collected were brightly coloured and slow-moving. They often flew in groups which were highly visible. Despite this, they were avoided by birds. This is typical of aposematic (warning) colouration. The colouring of some species from the same area was so perfect that even experienced naturalists could not tell them apart on the wing.
Once they were collected, and set out on a board so the details could be seen, it became clear they were not all of the same species, and often not from the same biological families. The similar warning colours of hornets, wasps and some bees is Müllerian if they live in the same geographical region, so that a predator might, before learning, choose any of them.
Tests show that birds do learn what to eat by sampling when they are young. All aspects of this situation have been the subject of research. Field and experimental work on these ideas continues to this day.
In Batesian mimicry, the mimic is a "sheep in wolf's clothing": it looks like something dangerous or which tastes disgusting, but in reality it is good to eat. As he was exploring the Amazon valley in the 1850s, Bates collected butterflies. He saw how some harmless butterflies looked like other species which were toxic. Birds avoided them, so "the mimics survived even though they were good food". This was the first scientific account of mimicry.
Hoverflies often visit flowers to feed on nectar. They are harmless insects which often mimic wasps and bees. They also fly in a slow, erratic fashion, rather like wasps and bees. Often their mimicry is not perfect, and you can easily tell them apart once they have settled. However, even an imperfect mimic might cause a bird to hesitate, and that may save their life.
Biologists still do research on Batesian and Müllerian mimicry. They study how the models differ in their foul taste; and what happens when the ratio of mimics to models varies. Quite often, it is only the female which is a mimic; the male carries the normal appearance of its genus. The females need more protection, while the males need to mate. A more subtle reason is that it halves the number of mimics, and so bolsters the effectiveness of the mimicry. Batesian mimicry might damage the warning effect if the frequency of mimics became high, because more young birds would taste them and be encouraged to try again. "The benefit of warning declines if there are more mimics".
This may explain cases such as "Papilio dardanus", an African swallowtail, whose females mimic a number of unpalatable species from the Danaidae: survival is higher when each mimetic form is rare relative to its model. The advantage is probably greater for the females, because males do not show the mimetic patterns; sexual selection probably helps to maintain this difference. These, and other issues, have been researched for many years.
With this type of insect the life is split into stages (see complete metamorphosis). The larva is the growth stage, the adult is the reproductive stage. The larvae, too, show camouflage, aposematic colour and mimicry. It is the larvae that pick up the offensive chemicals from the plants they feed on. However, larvae do not show differences between male and female, because reproduction is not their function.
In tropical countries, field research has shown that there are large numbers of species involved in mimicry. 54 species of "Heliconius" are recognised, with over 700 named colour forms. There are four (or perhaps five) assemblages of butterflies, which include the heliconiines and their mimics. These 'mimicry rings' are called "tiger", "red", "blue" and "orange" for short. Members of each ring tend to roost together at night, fly to similar habitats and at the same time of year. Mimicry rings include both Müllerian and Batesian mimicry.
Vavilovian mimicry occurs in plants where a weed comes to look like a crop plant. It is named after Nikolai Vavilov, a Russian plant breeder who discovered the idea. Before herbicides, weeds were plucked by hand. This has been done for thousands of years. The weeds come to look like the crop because the weeders pick those weeds which look most different. Vavilovian mimicry is caused by unintentional selection by humans. The weeds that survive pass on their genes. Gradually, all the weeds look more like the crop plant.
An example is rye, a common Mediterranean species. Rye was originally just a weed growing with wheat and barley. Weeding made it like the crop. Like wheat, it came to have larger seeds and more rigid spindles to which the seeds are attached. Rye is a tougher plant than wheat: it survives in harsher conditions. Having become a crop like the wheat, rye was able to become a crop plant in harsh areas, such as hills and mountains.
This type of mimicry is quite common. It is the bible metaphor of the "wolf in sheep's clothing". The mimicry works to entice a victim, who is then eaten, or otherwise taken advantage of. Angler fish, insectivorous plants and the cuckoo are all examples. All these groups are widespread, and there is no doubt that the aggressive mimicry is a successful life-style.
The next two examples introduce another metaphor, that of the "siren". The Australian katydid "Chlorobalius leucoviridis" can attract male cicadas by imitating the species-specific reply clicks of sexually receptive female cicadas. Playback experiments show that "C. leucoviridis" is able to attract males of many cicada species, even though cicada mating signals are species-specific.
Female fireflies of the genus "Photuris" emit the same light signals that females of other genera use as a mating signal. Further research showed male fireflies from several different genera are attracted to these mimics, and are subsequently captured and eaten. Female signals are based on that received from the male, each female having a repertoire of signals matching the delay and duration of the female of the corresponding species.
Luring is not a necessary condition however, as the predator may have a significant advantage by not being identified as such. They may resemble a mutualistic symbiont or a species of little relevance to the prey.