Wingspan 40-50 mm.
An immigrant species which sometimes occurs in large numbers, especially if there's an extended period of warm weather or southerly airflow.
It flies in the sunshine and hovers in front of flowers, sipping the nectar with its long proboscis, very much like the hummingbird which gives it its name.
The larvae feed on bedstraw (Galium), and some of these may hatch and give rise to autumn adults in an influx year. Taken from UK Moths website.