Eristalis tenax is a hoverfly, also known as the drone fly (or "dronefly"). It is migratory and cosmopolitan, the most widely distributed syrphid species in the world, and is known from all regions except the Antarctic. It has been introduced into North America and is widely established.
It looks somewhat like a drone honey bee, and likely gains some degree of protection from this resemblance to a stinging insect. The adults are called drone flies because of this resemblance. Like other hover flies, they are common visitors to flowers, especially in late summer and autumn, and can be significant pollinators.