Here are some 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 toxic 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 Muellerian mimcry complex (all members are toxic) 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 large “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.
Another variation on the theme of small eye spots and artificial heads is their use to direct the strike of predatory birds away from the vulnerable body to the periphery of the wings where damage is not of much consequence. The eye spots of the buckeye seem to fit into this category. Notice the bites taken out of the edges of the wings near the eye spots. The peculiar false heads with eye spots and imitation antennae of the hairstreaks are a more complex design to misdirect attacks.
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 advertise 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.