Mydas fly on mint.
Mimic fly, Mallota posticata, on viburnum.
When we think of pollinators, we often think of bees and butterflies; flies might not come to mind. However, the Penn State College of Agricultural Science noted that flies are the second most important pollinators after bees, especially in environments that have fewer bees. Unlike other pollinating insects that have two pairs of wings, flies have only one pair of wings, hence the name of the order Diptera, which means two wings. Most flies do not have specialized pollen-carrying hairs like bees and are therefore generally thought to be less efficient pollinators by comparison.
Flies serve many purposes in the garden.
- Pollinators. Flies can be seen on multiple garden plants, including a range of annual and bulbous ornamental flowers. Some plants specifically pollinated by flies include pawpaw, skunk cabbage, goldenrod, and members of the carrot family. Some plants have evolved to be pollinated only by flies, such as the Amorphophallus konjac or Voodoo lily.
- Predators. Flies can be predators as larvae, adults, or both. The most common predatory fly is the robber fly or assassin fly (family Asilidae). They feed mainly or exclusively on other insects. The more delicate long-legged fly captures smaller insects (such as aphids and gnats), mites, and other tiny arthropods. The diet of the larvae of predatory flies varies by species.
- Detritivores. A detritivore obtains nutrition by feeding on detritus, organic matter made up of dead plant and animal material, or by feeding on feces. Detritivores and decomposers contribute to the breakdown of all dead and decaying material in any ecosystem; therefore, they play a crucial role in the cycling of nutrients. They are essential to most biogeochemical cycles, including the carbon, nitrogen, and phosphorus cycles.
A few interesting flies that I have observened in my garden are detailed below.
HOVER FLIES, family Syrphidae
Hover flies make up the insect family Syrphidae. Adults of many species feed mainly on nectar and pollen. Larvae (maggots) eat a wide range of foods depending on species, including plants; decaying plant and animal matter in the soil, ponds, and streams; and aphids, thrips, and other plant-sucking insects. Hover fly larvae are important for the biological control of these garden pests.
Syrphus ribesii is a very common Holarctic species of hoverfly. Its larvae feed on aphids. In common with many other species of hoverfly, the eyes of the males meet on the top of the head, and the eyes of the females are widely separated.
Sphaerophoria contigua. A species of syrphid fly that is a predator of aphids when in the larval stage.
Common oblique hover fly, Allograpta obliqua, is a North American species. The larvae are important predators of aphids, and the adults are pollinators.
MIMIC FLIES, family Syrphidae
Some species in the Syrphidae family have appearances that mimic other insects, usually bees or wasps.
The Mallota posticata is a widely distributed genus of hover fly well known for its bee-like appearance. As larvae they are detritivores, rat-tailed maggots that filter feed in water-filled tree holes, and as adults they are nectarivores.
Williston’s Wasp fly, Sphiximorpha willistoni, is a rare species of syrphid fly found in eastern North America. It is a strong wasp mimic with darkened forewing, elongate antennae, black and yellow markings on the thorax, and banded yellow markings on a thin-wasted abdomen. When I photographed the individual here, I thought it was a small wasp.
OTHER GARDEN FLIES
Common green bottle fly, Lucilia sericata, on oxeye daisy.
The common green bottle fly, Lucilia sericata, is a blowfly found in most areas of the world and is the most well-known of the numerous green bottle fly species. The larvae feed exclusively on dead organic tissue. The adults eat carrion and feces as well as pollen and nectar. They are important pollinators in their native ranges and important agents of decomposition. The pollen, which the flies can digest, may be used as an alternative protein source when they cannot reliably find carrion.
They are particularly attracted to sapromyophilous flowers that exude a carrion-like odor, such as the Amorphophallus konjac, which trick the flies into pollinating them by mimicking the scent of a corpse. These flies also frequently visit myophilous flowers such as the oxeye daisy — they are attracted to the color yellow and to the scent of flowers. This indicates that the flies are attracted to flowers not only for their smell, but also for their pollen.
The black-horned gem, Microchrysa polita, is a species of soldier fly found in Europe, Asia, and North America. It breeds in dung, rotting vegetable matter, and compost heaps. Adults feed on flower nectar, and larvae feed on decaying organic matter.
Black-horned gem, Microchrysa polita, on dahlia bud.
Mydas fly on mint.
The Mydidae family, or Mydas flies, are a cosmopolitan family of flies that are generally large in size, including the largest known fly, Gauromydas heros. Many of the species are also mimics of stinging hymenopterans, especially wasps. Most mydids are found in arid and semiarid regions, but they are also found in other habitats. When immature, they prey on soil-dwelling insect larvae, especially on coleopteran (beetle) larvae, including white grubworms and the larvae of other beetles. Mydas flies are infrequently encountered because the adult life span is very short.
Long-legged flies, family Dolichopodidae. Adults are predators similar to miniature robber flies that capture smaller insects, including gnats and aphids, mites, and other tiny arthropods. Their mouthparts are knifelike and they use them to pierce their prey.
The diet of the larvae varies by species: some are predatory, others eat plants, and others scavengers that eat decomposing organic matter such as rotting vegetation.
Long-legged fly.
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