Flies in the Garden
Mydas fly on mint.
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, but some plants specifically pollinated 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.
- Parasitoids. As its name suggests, a parasitoid fly is a parasite. The larva of the fly lives inside another insect, which is referred to as the host. The larva feeds on the host’s internal tissues until the host dies and the larva completes its development. The tachinid fly is a common example that lays eggs on caterpillars, often those of the Monarch butterfly. Many parasitoid flies have specific host species. Because they can help control pest populations, parasitoid flies may be considered beneficial insects in pest management programs.
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.
Common flower fly, Genus Syrphus. Very common garden fly; its larvae feed on aphids. Like many other species of hover fly, the eyes of the males meet on the top of the head, and the eyes of the females are widely separated. Many of the species in this genus look so similar that they are difficult to differentiate.
Thick-legged hover fly, Syritta pipiens, on cleome seed pod.
Hover fly, Eastern Forest Sedgesitter, Platycheirus obscurus.
The tufted globetail, Sphaerophoria contigua, is a species of syrphid fly that is a predator of aphids when in the larval stage. Shown above and below on dahlias.
← Thick-legged hover fly, Syritta pipiens, is one of the most common species in the Syrphidae family. It resembles many predatory hoverfly species, but it is not predatory. Larvae can be found in rotting organic matter, including manure, silage, and garden compost, on which they feed. Adults are critical pollinators for a variety of flowering plants, and the species hosts various parasitic wasp species. They play an important role in environmental functionality and can serve as bio-indicators: their abundance can reflect the health of the environment.
Hover fly, Platycheirus scutatus.
Platycheirus scutatus. The larvae feed on aphids, and the adults feed on a wide range of flowers. They have multiple broods throughout the warmer months and have a very long flight period. These hover flies may stay active during cold weather.
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.
Eastern Hornet Fly, Spilomyia longicornis
The larvae can be found in holes in rotting trees, but the adults spend most of their time around flowers to obtain pollen and nectar for food and for mating. The females of this species need pollen for reproductive development. They also consume nectar from flowers and use that energy for their hovering behavior.
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. I feel lucky to have documented them on a few occasions.
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.
Picture-winged fly, Delphinia picta, on eryngium leaf.
Picture-winged flies. Delphinia picta, a species of picture-winged fly in the family Ulidiidae, is a detritivore that eats decaying plant matter. They can be found in many locations, including temperate deciduous forests, landfills, shaded fields, and swamps. The female lays eggs in decaying herbaceous material, and the development of the larvae and pupae is affected by the amount of daylight. One generation lives from May to July, and the second generation overwinters as mature larvae.
Lance Fly, Family Lonchaeidae
The Lonchaeidae family or lance flies includes 610 described species in 10 genera. They are small flies with varied biology. Larvae of different species feed on plants, damaged plant tissues, or feces, or they can be predators. Correspondingly, the larvae live under bark, in decomposing wood and other decomposing plant residue, and in dung. Larvae of some species cause formation of galls on plants while those of other species live in juicy fruits. Adult flies are found on trunks of trees, logs, cut wood, leaves of shrubs, and in grasslands. Some species are agricultural pests of plants, including cassava, passion fruit, fir and spruce trees, and figs.
