There are some little flies that visit flowers with great frequency. Naturally, they are called flower flies; although the British prefer the name "hover flies", which describes their behavior very accurately. They are very numerous in the garden; but if you dislike house flies you don't need to worry about flower flies; they are rather pretty. You probably didn't notice their presence thinking that they were bees, rather than flies.They are excellent impersonators of stinging insects such as bees and wasps and they probably fool hungry birds into thinking that they may get stung but these little "bees". This strategy seems to work very well for them, so they can go feeding on flowers unmolested by these winged predators.
In their visits to flowers they accomplish some pollination. They may not be as efficient as bees, but their sheer abundance makes them important pollinators of wild flowers. But there is something else that these flies do that makes them very welcome in the garden: The larvae of some of them feed on aphids.
This is such an important task that they deserve more attention than they get from plant lovers. We don't appreciate them enough.