Thursday, October 01, 2009

Syrphus fly, a pollinator and aphid eater

Syrphus fly on Queen Anne's lace. © Beatriz Moisset. 2009
Among the many flower flies there are some that are beneficial to the garden in more ways than one. Flies of the genus Syrphus and also some of their relatives are moderately good pollinators when compared to bees. They visit flowers frequently because they need nectar to fuel their flight; the females also need protein rich pollen for their eggs to grow and mature. The reason why they are not as good as bees is that their bodies have very little hair so pollen doesn’t adhere very well to them. However what they lack in efficiency they make up in sheer numbers. In some instances flies are more abundant than bees and may end up providing a better service to some flowers.

The genus Syrphus counts with several species in North America. They are very hard to tell apart; as a matter of fact they are also hard to differentiate from their close relatives: Eupeodes. Entomologists need to examine them under the microscope and look for minute details of wings and other body parts to identify each species.

Beginners have an even harder time and frequently confuse them with bees, although their single pair of wings should be a clue that they are flies not bees. They are considerably smaller than honey bees but there are many species of native bees about the same size as Syrphus. There are other ways of telling these flies apart from bees; their antennae are very short and with a funny shape with a little appendage called an arista; their eyes are enormous and their legs skinnier than those of bees. As I mentioned before they are nearly hairless. Although they may look like bees you don’t need to fear their sting because they have none.

Larva feeding on aphids on a milkweed's leaf. © Beatriz Moisset. 2009
What is interesting about these flies is that in addition to being pollinators they are very helpful to your garden as larvae because they eat aphids. The female lays her eggs near an aphid colony. The tiny maggots that emerge from the eggs are blind and legless but they don’t seem to need those organs to find their food.

They promptly go to work helping themselves from the colony. It is odd to see some completely unconcerned aphids near a maggot devouring one of its sisters; they may even come close to inspect it. Each maggot needs a large numbers of aphids and about a couple of weeks to complete its growth. It finds a place to pupate, under a leaf or on the ground and emerges in a few days ready to start raising another family of pollinators/aphid eaters. Gardeners familiar with these qualities of Syrphus flies strive to grow the plants that will provide pollen and nectar to them to ensure that they do their duty as aphid patrol.

List of Articles

Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2009

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