A “Hummingbird moth.” A family of insects (Sphingidae), when in the caterpillar stage, is known as hornworms. About two dozen species of hornworms are found in Colorado (where this photo was taken). Although all feed on leaves of various plants, most are innocuous, attracting little attention and causing little, if any, injury to garden plants. Tomato and tobacco hornworms, which feed on tomatoes and a few related plants, are an exception, being true garden pests.
Adults of all hornworms turn into large moths, known as “sphinx” or “hawk” moths. Most fly at might and are rarely seen. A few species, however, fly during cloudy afternoons and at dusk when they feed at flowers in a manner similar to that of a hummingbird.