Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 08 table of contents.
Throughout the animal kingdom, insects preyed upon by birds often have patterns of pigment that resemble eyes. Eyespots scare birds away or divert their pecks to the wing instead of the body. The secret to understanding how tiny eyespots could scare birds is to realize that birds are pattern-recognizing experts, but they are relatively insensitive to the size of a pattern. They have to ignore size because they fly at different altitudes and must recognize visual patterns no matter how large or small they might appear from various heights. So birds respond to the configuration of a pattern more than its size. If an insect preyed upon by birds happens to develop a pattern that resembles an eye spot, it is less likely to be eaten and more likely to survive and reproduce.
Why do some moths have eyespots on their wings?
Why are birds instinctively afraid of eyespots? Predators, as a rule, have large front-facing eyes. This helps them localize their prey exactly, using binocular disparity. Animals that prey on birds—owls, primates, and cats—typically have large, staring eyes. Therefore the birds are showing a biologically prepared form of avoidance. Birds that avoid eye-like patterns are themselves more likely to survive and reproduce.
The Hawk Moth
Here is the Hawk Moth of New Caladonia. The name Hawk Moth is apt, but one student suggested Tiger Moth might be more appropriate; the forward-facing eyes and rounded nose have a distinctly feline look. Cats love to prey on birds, so such a pattern might scare birds.
No moth looks as cat-like as the Rosie moth.
What was Swynnerton's experiment?
There is a second way in which eyespots protect butterflies. Birds that attack the insect often peck at the eyespots, leaving the butterfly or moth free to fly away. Swynnerton painted conspicuous eyespots on butterflies visiting clumps of bananas next to his verandah. He caught the painted butterflies later and observed that 47 of 51 butterflies had injuries from bird pecks. Of the 47 injuries, 36 were at or near the eyespots (Cott, 1940/1957). A peck on the eyespot may reduce the butterfly's flying efficiency, but at least the butterfly can survive to reproduce.
What did University of Wisconsin researchers discover?
Eyespots are so common among butterflies and moths that they have attracted considerable research attention. A team at the University of Wisconsin identified specific genes and proteins that controlled eyespot formation (Carroll, Gates, Keys, Paddock, Panganiban, Selegue, and Williams, 1994). Within a few years, they identified the specific sequence of changes in gene expression that led to the evolution of eyespots (Keys, Lewis, Selegue, Pearson, Goodrich, Johnson, Gates, Scott, & Carroll, 1999).
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Copyright © 2007-2011 Russ Dewey