Here’s Looking at You, Kid

Animals with Eyes in the Back of their Heads

For this, the final story of Season 4, we are continuing the trend from last week’s story, and yet also coming full circle. Like the previous story, the mimicry showcased here is not of another species. However, the purpose for it is primarily defensive, much like the species showcased in the first half of the season. More specifically, it involves the mimicry of one’s own body parts for the purposes of fooling predators. This is known as automimicry, meaning the mimicry of self.

Take a close look at the owl pictured above. It is a northern pygmy owl, Glaucidium californicum, a small bird about 15cm long native to North America. While its posture, talons, and tail indicate that this individual is facing towards the camera, a close inspection of the head shows that it is actually turned away approximately 180˚, a common ability among owls (though they are unable to do so for a full 360˚ circle like you see in some cartoons). The feathers on the back of the head form a pair of ‘eyespots’, which make it appear as though the owl is looking at you even when it is not.

Many species in the genus Glaucidium, the pygmy owls, have this feature. Because of their small size, they can become a target for larger birds of prey. The eyespots give the impression to a predator that the owl is hyper-vigilant, decreasing the likelihood of an attack. Mimicking eyes also occurs on many species so that if an attack does come, it does not target vital area. For example, the foureye butterflyfish, Chaetodon capistratus, below.

Native to the western Atlantic Ocean, these fish are commonly found on coral reefs. The large dark spot on its rear, surrounded by a white ring, resembles and eye. The true eye is obscured by a dark stripe and difficult to detect. Most predators will attack the prey’s head first. When encountering such a predator, the butterflyfish will present itself in a manner that suggests its tail is actually the head, even swimming backwards slowly to add to the ruse. This decreases the chances of a fatal strike.

Fish are not the only animals with such a combination of mimicry and behavior. Some snakes also have eyespots on their tails and will move backwards from a predator while presenting the tail as its head. Other species go even further. The gray hairstreak buttefly, Strymon melinus, will land at rest with its head facing down and its tail in the air. That tail is complete with both eyespots and fake antennae to more closely resemble the entire head of the insect.

In this way, a predator is more likely to strike at the less vital tail than at the head. While any damage sustained from a predator will have a detrimental effect on that individual, it will not necessarily be life threatening. It is that key difference in outcomes that gives defensive automimicry its potency. A minor injury (or even a crippling one) is preferable to death if the individual in question is still able to pass its genetic material to the next generation via reproduction.

For one last time, imagine yourself in the role of the duped organism. You are a bird of prey (perhaps a much larger owl) and you see a pygmy owl sitting on a tree branch. Your chances of a successful attack increase (and the chances of personal injury to yourself decrease) if you can strike from surprise. However, it appears like your quarry is always looking at you. Would you be willing to take the risk? Or, perhaps you are a different predators that feeds on fish, snakes, or butterflies. The coloration of your target, as well as its behavior demonstrates which end is the head to you. This is your ideal attack area. However, when you strike, your prey survives the initial attempt and may even be able to escape because you actually attacked a different part of the target that only looked like its head. Again, the inability to differentiate between different parts of its body have cost you a meal.

In the end, mimicry is designed to fool the senses, and the closer a mimic resembles a model, the more successful it will be. Similarly, the better a potential dupe is at ‘sniffing out’ a mimic, the more successful it will be. As with many instances of competing pressures, this can lead to an ‘evolutionary arms race’ with mimics developing more and more elaborate disguises and the duped individuals developing methods of seeing through the subterfuge. As with all such selective pressures and situations, the ‘battle’ has no true end. It will continue on until one of the components is removed, either a species as a whole or the survival or reproductive benefit of that instance of mimicry.

That wraps up Season 4 on mimicry. Again, I’d like to thank my friend Bree for requesting this topic. I’ll be back in one month with a whole new set of stories for your enjoyment. If you like my stories, please like, subscribe, and share them. If you have an idea for a topic for a future season, let me know and if I use it, I’ll give you a shout out in my introductory post.