The All Seeing Eye

December 23, 2013

Nature Notes by Bill Dunson

Our most important and complex sense organ, the eye, serves as a window to the world around us, but in many animals it may be the primary means by which predators recognize and subsequently direct their attack of prey. Thus it is interesting that many means of camouflaging the eye have developed.

In some animals there seems to be minimal camouflage of the eye. Consider the yellow rat snake in which the dark eye is very obvious against a lighter background. The bullfrog also seems to make little attempt to hide the pupil of the eye; the iris contains speckling which may be a type of camouflage. Both of these are predators which are able to move quickly to escape. Yet a large aquatic herbivore, the peninsula cooter turtle, has a remarkable method of hiding the pupil of the eye with a dark line completely across the iris. As adults these turtles have few predators other than large alligators but it is apparent that there has been evolutionary selection to hide the pupil.

A common method of hiding the eye is to enclose it within a dark area on the head, as shown by the least tern and black skimmer. It is very interesting that the eye usually falls just on the edge of the dark area of feathers, completely hiding its presence. It is certainly possible that the importance of this camouflage may not be for protection solely against predators but against members of their own species who might damage the eye with their beaks. Perhaps if the eye is too obvious it might also alert prey and make hunting more difficult. Hiding the eye within a patch of head color also allows an animal to keep the eye lid open to monitor for predators while minimizing detection, and allowing for any necessary quick action to escape. If directly gazing at a predator might precipitate an attack, hiding the eye could be a crucial strategy for protection.

The critical role of the eye in directing or deferring predatory strikes is shown most impressively by a large number of insects which have fake eye spots on their wings or bodies. Some caterpillars have eye spots to mimic snakes. Many butterflies and moths have eye spots to deflect the strikes of birds to less vulnerable parts of the body. This is very well illustrated by the common buckeye which has a series of eye spots on the periphery of its wings. As the butterfly ages it is common to see that pieces of the wings are missing along the edge where birds have attempted to capture their prey.

As is often the case, we are amazed by the beauty and diversity of color patterns in animals, and how well they serve to enhance survival under different conditions. The common use of camouflage to hide the eye indicates how sensitive predators can be to a small aspect of the overall coloration of prey, and how finely the evolutionary mechanisms act to improve the chances of survival. In realizing this it encourages the naturalist to be more perceptive in observing and analyzing the differences among animals in their attempts to hide their eyes from the surrounding world.

Bill Dunson, Englewood, FL, and Galax, VA

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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