True or False: How Insects Fool Birds

One might think that nature would not lie, but it can sometimes be difficult to discern truth from what is essentially falsehood in nature. The reason for this is obvious- a bluff can be as succesful in avoiding predation as in winning a hand in a game of poker. So the ability to deter a predator can sometimes be obtained cheaply by looking as if you are venomous or toxic, without possessing the necessary poisons or delivery system. The evolutionary reason for the common occurrence of such mimicry is that it is probably easier in terms of genetics, physiology, biochemistry and morphology to “talk the talk” than to “walk the walk.” But this poses a huge dilemma for predators suuch as birds; how do they tell the difference? We do know that birds are quite discerning in picking out insects among foliage. The degree to which some insects are camouflaged is quite remarkable, and presumably due to the capture of any insects that stand out a little bit more than others. Yet there are numbers of insects that are brightly colored- likely advertising their toxic and/or posionous nature. Birds either learn by experience, or in some cases are genetically programmed to recognize colors that identify potentially dangerous prey.

Here are three examples of toxic moths and butterflies that birds in my Florida yard must deal with. The polka dot moth or oleander moth feeds as a larva on exotic oleanders and picks up toxins which are passed on to the adult, where this is advertised by bright colors. However the shape of the wings and body and general behavior of this unusual day-flying moth also mimc a wasp, giving birds two types of clues that this is a creature not on the lunch menu. Two brightly colored but very different butterflies are the zebra and the Gulf fritilllary, one black and yellow and the other orange and black. Both feed on poisonous passionvines as caterpillars and the toxins retained in the body protect the adults which advertise their toxicity with bright colors. The Gulf fritillary also seems to be part of a mimcry complex with milkweed butterflies (monarch, queen, soldier) and the viceroy (caterpillar eats toxic willow) which all have a generic orange and black pattern, making it easier for butterflies to learn the lesson that they should not be eaten.

Three equally striking examples of moths and butterflies that look dangerous but are not, are the Wittfeld’s forester moth, the polyphemus moth, and the caterpillar of the tiger swallowtail. The forester moth is another brightly colored day-flying moth, as is the oleander moth, a general indicator of some protection from birds. It also has a rather hurried and jerky flight pattern as does a wasp, and has fuzzy orange “socks” on its legs; these orange structures have been interpreted as mimicking the pollen baskets of bees. The beautiful polyphemus moth is well camouflaged at rest during daytime, but when disturbed it opens its wings revealing an amazing set of “eye spots” that are believed to scare bird predators by their resemblance to the face of an owl. Most song birds which eat insects are quite afraid of owls and even the simplified version of large staring eyes presented by the wings of this moth apparently affords it some protection. A somewhat similar effect is found on the caterpillars of various butterflies such as the tiger swallowtail shown here. It has two “eye spots” which may remind birds of snakes which they also tend to be afraid of.

So we have an interesting conundrum that is presented to birds as predators on insects. Insects that are toxic to eat or possess venoms generally advertize this fact with bright colors and characteristic shapes and behaviors that birds recognize as dangerous. Yet a number of other palatable and harmless insects have taken advantage of this fact to protect themselves in a clear case of false advertising. Yet what is a bird to do- take a chance or not? Obviously they find it very difficult to distinguish among the the real deals and the imposters. Try this yourself when you next see an insect advertising itself with bold colors and behavior and you will develop a better appreciation of the difficult choices that can face birds in their daily quest for food.

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net

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