Joan McGowan sent me a photo of a caterpillar she has in her garden in Florida (but which occurs widely in eastern N. America) that has been eating her exotic penta plants that are good for attracting butterflies that feed on nectar. When she described it orally as a brown caterpillar with eye spots I thought it might be a swallowtail, but the photo showed numerous eye spots and a spine or horn on the end of the body that clearly identified this as a Tersa sphinx moth or hornworm, Xylophanes tersa.
The caterpillar seems to be trying to mimic a snake, as does the unrelated but somewhat similar tiger swallowtail caterpillar. This may allow these caterpillars to feed somewhat exposed to predation. It is interesting that the adult moth (see photos from the web) is quite inconspicuous and drab, except that the hindwings seem to have a pattern that when suddenly revealed might serve to distract predatory birds. I am not aware that either life stage is toxic or distasteful.
Sphinx, hawk or hummingbird moths generally fly at night, feed on nectar ,and have adopted a similar high energy life-style to their namesake the hummingbird. To be able to fly so fast and hover they must eat a lot of high-energy food. They are remarkable in many ways although many people dislike them for their voracious appetites for some vegetables and flowers.
So here we have another of many examples of how bird predation has lead to coloration that tends to protect insects through a bluff. Once again it appears birds are quite careful in what they eat and may be dissuaded from attacking an insect by a ruse that would not serve to convince us. So does this mean that birds are stupid, or that they are just as smart as they need to be, at least most of the time?
Bill Dunson, Englewood, FL & Galax, VA