There are many species commonly known as "hummingbird moth". This one is White-lined sphinx hummingbird moth or Hyles lineata according to Butterflies and Moths of North America. Adults are just over two inches long with a wingspan of up to three inches making it quite a large insect. This moth is commonly found throughout North and Central America. By hovering over a flower instead of landing, the moth resembles a hummingbird and sometimes you have to look twice to be sure, especially when it's on the hummingbird favorite Salvia greggii.
This sequence is particularly fascinating as you can see the proboscis curl as it is retracted.
According the Wisconsin Master Gardener's site Hyles lineata caterpillars were used as food by Native Americans. I'll let you read about it on your own as the description of the process is not exactly yummy. While they are not considered prolific pollinators they are the key pollinators of the rare lemon lily in California. The caterpillars, which are a type of hornworm, enjoy some of our most common garden plants such as Four o'clocks, purslane, grapes, evening primrose and tomatoes. In spite of that I hope seeing this one means there will be even more around.