This "hummingbird moth" is also known as the White-lined Sphinx Moth (Hyles lineata), and it is one of several types of moth of the family sphingidae that are often mistaken for hummingbirds. The sphinx moth is so named for a posture that a threatened caterpillar assumes being reminiscent of the Egyptian Sphinx monuments.
Some moths, like the Snowberry Clearwing Moth may resemble hummingbirds to a greater or lesser degree than this species, but all members of the family sphingidae sip nectar from flowers on the wing as do hummingbirds, and a few even in broad daylight, although these sightings were crepuscular. The sound of this moth's wing beat is remarkably similar to that of a hummingbird's. Scroll down
Just as hummingbirds are pollinators of certain coevolved flowers, so is the "Hummingbird Moth" hovering before this Dune Primrose (Oenothera caespitosa). The white petals are highly reflective, and visible to the moth by starlight alone.
Within minutes of the bloom the moths arrive sounding just like hummingbirds. The first time I witnessed this wonder of nature, I remember asking myself, "isn't it too late in the evening for hummingbirds?"