Hoverflies are often sometimes called flower flies or syrphid flies, and they are often mistaken for bees or wasps. The adults feed on nectar and pollen, and can be seen hovering over flowers before landing briefly to sip nectar or eat some pollen. While adults of many species feed mainly on nectar and pollen, the larvae eat a wide range of foods such as decomposing plant and animal matter. In some species the larvae are insectivores and prey on aphids, thrips, and other plant-sucking insects. This makes them a natural predator and necessary for the balance of nature. Organic control, if you will:>)
As you can imagine, these cute insects can be important in plant pollination. They are completely harmless so don’t be fooled by their bee and wasp mimicry which probably serves to scare away predators.
About 6,000 species are known throughout the world. Hoverflies are found on every continent except Antarctica.
You can read more here: (the first article is the better one)