There are certain flies known as hover flies or flower flies that visit flowers frequently. They accomplish pollination; perhaps they are not as efficient as bees in general because they are rather hairless, so the pollen doesn’t stick to their bodies as much as it does to bees, and also because they don’t visit as many flowers. But they are so abundant that their sheer numbers make them more important as pollinators than one would think.
Among them, there are a number that serve double duty in the garden. In addition to pollinating flowers, they lay their eggs in the proximity of aphids; their babies are voracious aphid eaters. There is one flower fly, Syrphus that is particularly good at this; there is no common name for this fly, perhaps because most people don’t notice them or confuse them with bees.
Syrphus flies, along with many of their relatives, masquerade as bees with a body that has yellow and dark brown stripes. They are smaller than honey bees, about the same size as many of the smaller native bees, such as some halictid or sweat bees. This mimicry serves them well, because hungry birds fear the sting of bees and mistakenly avoid these tasty flies. The imitation is so effective that many human observers get fooled too. If you observe them carefully, you will notice some differences from bees; first of all they have only two wings instead of four. But, more easily seen are their very large eyes, short antennae and thin legs.
Like many other flying insects, Syrphus flies visit flowers in search of nectar to fuel their flight, and pollen, for their proteins. It is known that females need these extra proteins to make eggs.
They are frequent visitors to a great variety of flowers, and since they have several generations each year, they continue visiting flowers through the seasons from early spring to late fall, switching from one type of bloom to another as flowers come and go.
The other beneficial job that they perform in the garden is aphid control. Adults don’t have strong jaws to catch and kill an aphid but the larva or maggot does and is hungry for proteins to feed its rapidly growing body, so it goes for aphids with gusto. After mating, females search for aphid infestations; they are likely to overlook small gatherings of aphids in search for larger aggregations that would warrant a steady supply of food to their babies. The maggots are blind and legless but have no trouble finding prey to feed on. They grow rapidly on this diet; when fully grown and ready to pupate, they hide under a leaf or drop to the ground. They emerge as adults in less than two weeks. The new generation wastes no time finding flowers and pollinating them in the process.