What you have seen is one of a number of moth species commonly called "hummingbird," "sphinx," or "hawk" moths. Look under the Family Sphingidae or browse images on our web site for common examples in North America. Or, look at your region's checklist to see a list of Sphingidae in your area.
The most commonly seen "hummingbird moths" of the Sphingidae family are the Nessus sphinx (Amphion floridensis), Snowberry clearwing (Hemaris diffinis), Hummingbird Clearwing (Hemaris thysbe), and White-lined Sphinx (Hyles lineata).
The Sphingidae are strong fliers, with a rapid wingbeat. Most are medium to large moths, with heavy bodies; wingspread reaches 5 inches or more in some species. Although a few are active in the daytime, most species in the group are active at dusk. Most, but not all, sphingids feed much like hummingbirds, hovering in front of a flower and sipping nectar through the extended proboscis. The proboscis rolls up like a party noisemaker when not in use, and may not be readily evident in a resting moth. Some species lack scales on large portions of their wings, and therefore have transparent or clear wings. These are commonly referred to as "clearwing hummingbird moths." (Note however that the scientifically accepted common name of "Hummingbird clearwing" refers specifically to Hemaris thysbe.)
Yet another common name for the group is "hornworms." The name comes from a hook or hornlike appendage protruding upward near the posterior end of the caterpillar (larval stage) of most species. Although the horn looks like it may be dangerous, it is in fact harmless. Unfortunately, the larval stage of some species can be very destructive to agricultural crops and ornamental plantings. The tomato hornworm (Five-spotted hawkmoth Manduca quinquemaculata), for example, feeds on potato, tomato and tobacco plants, and can cause severe economic loss in these crops.
You can help. As you will note on the About page, Butterflies and Moths of North America is a work in progress, and the distribution maps it provides show only scientifically verified occurrences of each species. If you saw a species of hummingbird moth and you don't know which one or you simply want to help us further this project, we encourage you to report your discovery. Because so many of these moths can be easily confused with other sphingid moths, it is absolutely essential to submit a clear photograph. Please note that not all of the Sphingidae are included in the Butterflies and Moths of North America database yet.