Flies are some of our most abundant pollinators but are often overshadowed by the more conspicuous bumble bees. Unlike the bees, however, flies have critical parts of their life cycle that do not involve visiting flowers. Every adult fly that takes nectar and transfers pollen begins its life in larval form, feeding in completely different ways. The flower flies (family Syrphidae) are small and numerous in the garden, many looking like miniature bees or wasps. One such fly, the tufted globetail (Sphaerophoria contigua), is a common sight at Thuya. Like many flower fly species, its larvae (aka maggots) are predators primarily of aphids, but also other critters such as mites or thrips. This is good to keep in mind if you are tempted to wage war on aphids. Eliminate them and you will eliminate the flower flies.
Another family of flies whose adults are often seen on flowers is the tachinids (family Tachinidae). Like flower flies, their larvae feed on other insects. For example, the larvae of the Gymnosoma fly shown here, feed on the larvae of stinkbugs and shield bugs (family Pentatomidae). In this case, they are not predators but are parasitoids - parasites that kill their hosts.
Our last example is a fly in the genus Leucophora, from the family Anthomyiidae. This family is commonly called the root-maggot flies, so named because the larvae of some species feed on plant roots. However, among the 2,000 or so species in the family, there are many other larval feeding strategies, such as feeding on other plant parts, grasshoppers, even dung. This fly in the genus Leucophora has larvae that are kleptoparasites or mining bees (Andrena), meaning they steal food or trick the bees into feeding them in their nest. They have this strategy in common with bee flies (Bombylius) and cuckoo bees (Nomada), both of which we have recorded at Thuya. We take this as a sign that our mining bee population must be quite healthy to support three species of nest parasites.
By Rick LeDuc, Thuya Garden Manager