Hover Fly

Learn more about Hover Flies

Syrphidae
(Diptera: Syrphidae)

Syrphid flies, also commonly referred to as hover flies or flower flies, are species of true flies in the family Syrphidae, one of the largest families of flies with over 6000 described species (Miranda et al. 2013, Terry et al. 2017, Chisausky et al. 2020). Syrphids are carnivorous in the larval stage, often feeding on aphids and other insect pests. Adults are nectarivorous, consuming honeydew, nectar, and pollen that females require to produce viable eggs. Some syrphid larvae are aquatic and can be found in stagnant water, however most species of syrphid larvae live on the surface of plants where they feed and develop. Because many syrphid larvae are voracious predators, they are seen as a viable biological control organism to control populations of aphids, thrips, mites, mealybugs, leafhoppers, and other soft bodied arthropods (Bugg et al. 2008). In addition, syrphid larvae are efficient predators that move along plant surfaces, where many of these insect pests are found. The larvae lift their heads to feel for prey, seize and consume their insides before discarding the exoskeleton. Each larva can consume up to 400 aphids during development. When syrphid larvae are abundant, they may reduce aphid populations by 70 to 100%.

Adult syrphids are efficient pollinators of many wild plants (Colley et al. 2000, Ssymank et al. 2008), and because syrphids do not provision their offspring in a nest as do bees, some species are able to range over more of the landscape and carry pollen longer distances than other pollinator species (Lysenkov 2009, Rader et al. 2011, Chisausky et al. 2020). However, despite these pollination service benefits, they are often underappreciated when compared to other pollinator species such as bees and wasps (Chisausky et al. 2020).

Appearance of syrphid fly larvae

Syrphid fly larvae vary in size from 4 to 18 mm in length on average with yellow, green, white, or brown body coloration. The larvae of syrphids may differ in appearance due to their location and feeding source, however the contents of their body are often visible as the body wall is somewhat translucent. Larvae are slug-like maggots that are wrinkled and tapered anteriorly. Most predatory syrphid species lack prolegs, but may have lines in the segmented body that can give the appearance of small legs. Syrphid larvae also have a tapered head region due to a lack of a head capsule.

Adult syrphid fly appearance

Adult flies vary in length from 3 to 13 mm depending on species. The adults all have a single pair of wings and black or brown bodies that are often marked with brightly colored stripes or spots covering abdomen and/or thorax. Because they often exhibit stripes of yellow they are often mistaken for wasps or bees. Their resemblance to bees and wasps is a form of mimicry to ward off predators. Syrphids can be distinguished by their single pair of wings, with white halteres, characteristic of all dipterans. The legs, mouthparts, and antennae of syrphid flies are not particularly long or distinct and are often brown, black, or tan in appearance.

Syrphid fly life cycle

The life cycle of syrphids varies among species and depends heavily on environmental conditions and feeding sources. In optimal conditions, single white eggs are laid on leaves infested with prey or other suitable food source. After hatching in about 3 days, larvae develop through several instars (typically 3) over a period of 1 to 3 weeks. The last instar turns into tan-brown teardrop-shaped pupa on the host plant or in the soil. Unless the pupal stage remains overwinter, adults emerge in 1 to 2 weeks with between five and seven generations occurring within a year.

Commercial availability vs. support of syrphid populations 

Due to the complex nature of their reproduction, only one species of syrphid is available for purchase from a commercial rearing company, Episyrphus balteatus from Koppert Biological Systems. Therefore, improved levels of syrphid predation can be achieved through attraction and support of syrphid populations, as well as other natural enemy species. Supporting populations of natural enemies involves maintaining diverse habitats, as well as planting varieties of flowering plants that offer essential nectar, and pollen that can frequently be critical to adult survival and oviposition.

Compatibility with insecticides and herbicides

Beneficial insects are often not compatible with commercially available insecticides, and the use of herbicides can reduce the floral and nectar availability, therefore, species of natural enemies such as syrphids should be supported in production systems with low-risks of non-target effects and agricultural regions where the survivability and compatibility of the insect and ecosystem is not challenged by pesticide susceptibility.