Not every animal is what it appears to be at first glance. African bushveld lizards often move with their backs arched, their legs stiff and their tails pressed against the ground, giving them the appearance of acid-spraying “oogpister” beetles. Some butterfly larvae can puff up part of their bodies, which have spots on them that look like eyes, so that they look like a snake’s head. Certain robber flies sport orange wings that resemble those of stinging tarantula hawks. Mimic octopuses pull a ruse where they change color and hide all but two arms, extended in opposite directions to look like a venomous sea snake.
These masters of disguise are what biologists call Batesian mimics—harmless animals that imitate the physical features or behaviors that other, dangerous animals (the “models”) use to advertise their toxins, venoms, or other defenses. Predators that avoid these warning signals instinctually, or have learned to from run-ins with the models, also avoid the mimics, and the fakers gain protection from them without having to develop weapons of their own. The trick is most effective at duping predators when there are lots of models around, or if the mimic does a really spot-on imitation when the model animal is rare.
One predator can throw a monkey wrench into the works: humans. People don’t face the same risk in attacking a dangerous model as other predators do, because they have a wide variety of protective gear and weapons at their disposal. And if a model animal is considered a pest or presents a threat to people or their pets and livestock, then an abundant model or very good mimicry—the very same things that protect a mimic most of the time—can make it more likely that people will attack mimic and model alike.
That’s the case for Finland’s smooth snake (Coronella austriaca), say biologists Janne Valkonen and Johanna Mappes. The snake lives in small, scattered populations across Europe and is listed as a specially protected species by the European Union. In Finland, they’re found only on the Åland Islands, and may soon be listed as endangered in the country.
Smooth snakes are harmless, but trick predators by mimicking the scale patterns of the venomous European adder (Vipera berus), and can also flatten their heads into the triangular shape typical of vipers to make the disguise even better. The adder is one of the most widely distributed snake species in Europe, so many predators are likely to leave it and anything that looks like it alone, giving the smooth snakes a good deal of protection. But the adder is also the only native Finnish reptile not protected by law and is “often abhorred and … frequently killed by people,” say Valkonen and Mappes. This presents a two-pronged problem for the mimics.
Let’s say a smooth snake is slithering around minding its own business, and a person comes along. They see the snake and, mistaking it for an adder, decide to kill it. Oops. One less smooth snake in the world. But even if that person had found an actual adder and killed it, this still costs the smooth snake in a more indirect way. If there are fewer adders around, there are fewer chances for predators to learn to avoid them and their warning signals, making the smooth snakes’ mimicry less effective at keeping them safe. Kill enough adders, and the smooth snakes’ disguises become worthless, leaving their tiny populations vulnerable to predators.
While there’s no systematic data on how frequently either of the snakes are killed by people, they’re both frequently found in residential areas and exposed to danger from humans. So, Valkonen and Mappes suggest, “for the successful conservation of smooth snakes in Åland, it seems crucial to also protect adders.” That would protect the smooth snakes from cases of mistaken identity and accidental killings, and also ensure that their anti-predator strategy remains intact. To save one snake, Finland might protect two, even if one them is neither rare nor particularly well-liked.