Flower flies may not live in large colonies like honey bees – in fact, more often than not they are solitary creatures - but they play a significant role in the pollination of many economically valuable crops. A great example of their work is seen in the hoverfly Allograpta obliqua. This species is common throughout Ontario and Quebec and chances are you have seen one without even knowing it. The larval stage of their lifecycle is of great advantage to farmers as they eat multiple aphid species which can cause severe crop loss, particularly in an organic garden or farm. Once grown, the adult flies serve to pollinate over 54 known species of plants including members of the squash, carrot, cabbage and legume families.
Providing the right conditions are present, these flies can accumulate. A large enough population might impact seed-saving practices by increasing the isolation distances needed to keep varieties pure. Despite their voracious diet for all things floral, flower flies tend to prefer heavily scented flowers so distractions such as a patch of the fragrant evening primrose can mediate their potential for increasing cross-pollination. Of course, the flies may also prefer to lay eggs in the flower patches instead, focusing their aphid-eating activities on less lucrative crops! One strategy to overcome this might be the entwining of fragrant flowers within the harvest crop, though this strategy has not necessarily been proven effective.
Many other flower flies play important roles as pollinators as well and their significance is largely based on your particular crops, the surrounding fauna, and geographic location. Remember that if you are harvesting seed for the following year and trying to maintain varietal purity while growing two or more of the same species, it is worth taking their activity level into consideration along with that of the better-known bees.