Sphinx moths are large and powerful flyers. They are also called hummingbird moths, because they sometimes hover and are about the size of hummingbirds, or hawk moths because of their fast, swooping flight. They usually fly at night but sometimes can be seen early in the morning or in late evening. I've sometimes been startled by the loud sound of their flight when they are nearby. I also remember once seeing a small moth flying near flowers and it just looked like a body with a blur around it. I could reach close to it and feel the wind from its wings, as if it was surrounded by a force-field.
The three moths pictured here are all different species. At left is a rustic sphinx (Manduca rustica). Below at left is a vine sphinx (Eumorpha vitis) and at right a Carolina sphinx (Manduca sexta). These moths have startling bright colors on their lower wings that are hidden when they are at rest. These are probably a type of defense against predators, in the form of surprise when the color is revealed. Hawk moths have long proboscises and feed on such flowers as trumpet vine and the enormous jimsonweed.
Sphinx moths derive their name from the defensive stance often assumed by the caterpillars: they hold the front part of their bodies up and hunched over like a sphinx. Another name for these caterpillars is hornworm, because of the pointed projection on the rear end of many species. Although the hornworms don't often occur in large numbers, their sheer size makes them quite destructive and they are usually evident by the large droppings and completely defoliated branches surrounding them.
The insect pictured above is a tobacco hornworm (larva of the Carolina sphinx). These large green caterpillars are found on tomato plants and also jimsonweed; we don't grow tobacco, so they have to settle for the other two plants. This hornworm is about as big as it will get and is ready to pupate. Because it was disturbed, it has assumed the "sphinx" stance.
The two hornworms shown above are the larvae of the snowberry clearwing (Hemaris diffinis), a rather small (for a sphinx moth) bumblebee mimic. The one on the left is young, while the one on the right is much larger and closer to maturity. These caterpillars come in two color phases: green and purple. Their preferred food source is the honeysuckle, and that is the only plant on which I've ever seen them.