Here's what Wikipedia has to say:
Macroglossum stellatarum, known as the Hummingbird Hawk-moth or sometimes the Hummingmoth, is a species of Sphingidae. Its long proboscis and its hovering behaviour, accompanied by an audible humming noise, make it look remarkably like a hummingbird while feeding on flowers. It shouldn't be confused with the moths called hummingbird moths in North America, genus Hemaris, members of the same family and with similar appearance and behavior. The resemblance to hummingbirds is an example of convergent evolution. It flies during the day, especially in bright sunshine, but also at dusk,[1] dawn, and even in the rain, which is unusual for even diurnal hawkmoths.[2] Its visual abilities have been much studied, and it has been shown to have a relatively good ability to learn colours.[3]
