The natural world is full of surprising strategies animals use to survive. From camouflage to alarm calls, species have developed diverse adaptations to navigate their environments and avoid becoming prey.
Understanding Batesian Mimicry
Batesian mimicry is a form of biological resemblance where a harmless species evolves to imitate the warning signals of a harmful or unpalatable species. This strategy allows the harmless mimic to gain protection from predators by appearing dangerous without actually possessing any defenses. The concept was discovered by the English naturalist Henry Walter Bates, who studied butterflies in the rainforests of Brazil.
This mimicry system involves three main participants: the “model,” the “mimic,” and the “dupe” or “predator”. The model is the harmful or unpalatable species that possesses a genuine defense, such as toxicity, a foul taste, or a sting, often advertised by conspicuous warning coloration. The mimic is the harmless species that imitates the model’s warning signals, benefiting from the predator’s learned avoidance of the model. The dupe, also known as the signal receiver or operator, is the predatory species that is deceived by the mimic’s resemblance to the model.
For Batesian mimicry to be effective, the model species typically needs to be more abundant than the mimic species. If mimics are too numerous, predators might have positive experiences with the harmless mimics, leading them to disregard the warning signals of both the mimic and the true model. The mimic essentially “parasitizes” the honest warning signal of the model, gaining protection without the metabolic cost of producing toxins or other defenses.
Common Examples in Nature
Batesian mimicry can be observed across various animal groups. One example involves hoverflies (family Syrphidae) mimicking stinging insects like wasps or bees. These harmless flies often display black and yellow stripes, similar to their stinging models, and some even mimic the flight patterns and sounds of bees.
Another example is seen in certain snake species. The non-venomous scarlet kingsnake ( Lampropeltis elapsoides) mimics the highly venomous coral snake (Micrurus fulvius). Both snakes exhibit striking patterns of red, black, and yellow bands. While the coral snake’s pattern typically has red bands touching yellow bands, and the kingsnake’s pattern has red bands touching black bands, the overall resemblance is often close enough to deceive predators.
In the butterfly world, some palatable butterflies mimic the appearance of toxic species. For instance, some Dismorphia butterfly species mimic various Ithomiini butterflies, which are unpalatable to predators. Although the viceroy butterfly (Limenitis archippus) was once considered a Batesian mimic of the toxic monarch butterfly (Danaus plexippus), more recent studies suggest that the viceroy itself is unpalatable, making this a case of Müllerian mimicry.
The Evolution of Mimicry
Batesian mimicry arises through the process of natural selection, where predation acts as a driving force. Within a population of harmless species, individuals that happen to possess even a slight resemblance to a dangerous model are more likely to survive encounters with predators. Predators that have learned to avoid the model will also avoid these mimics. This increased survival allows the better-mimicking individuals to reproduce and pass on their advantageous traits to their offspring.
Over successive generations, this selective pressure leads to the refinement of the mimic’s resemblance to the model. The mimic’s appearance becomes more precise as individuals with traits that more closely match the model’s warning signals are favored. This ongoing process can create what is sometimes referred to as an “evolutionary arms race”. Mimics are under continuous selection to improve their deception, becoming more convincing in their imitation.
Conversely, models may experience selection to evolve phenotypes that allow them to escape from these “parasitic” mimics. If mimics become too common, predators might start to learn that some individuals with the warning pattern are actually harmless, potentially increasing predation pressure on the true models. However, evidence for models evolving away from their mimics in natural systems is less common than the evidence for mimics evolving to resemble models. This suggests that while mimics are constantly refining their disguise, the selective pressure on models to change their appearance due to mimicry might be weak or rare in many instances.