Other Pollinators: Flies


Flower pollination by a fly. Bees are often seen as the main insect pollinators and as they are certainly playing a very important role in pollinating many plants we should not forget all the flies. Many flies will visit flowers for pollen and nectar as well.

There are around 7000 known species of flies (for comparison: there are about 250 species of bees). Flies have only one pair of wings; the second pair is converted into stalked knobs which are called halters or balancers. Most adult flies have well-developed wings and fly readily and many of them are important flower visitors.

Flies usually feed on exposed fluids but can also eat small solid particles such as pollen grains. The taste organs are mainly located near the mouth but flies can also taste with their legs (taste organs in the legs are located in the tarsi, the end part of the legs). The legs of Blow flies (Calliphoridae) for example are 100-200 times more sensitive to the taste of cane sugar (sucrose) than the human tongue. Some flies locate suitable flowers by following the distinctive flower scent which they detect with their antennae. Most flower-visiting flies also have large eyes and at least the higher developed flies have colour vision which helps with finding flowers from afar.

Fly anatomy/ In contrast to many bees, flies still fly in less favourable weather conditions and on cold, windy and overcast days flies are often the only flower visitors you will see. Plants growing in damp, shady places such as woodlands would struggle to attract bees but flies are often abundant in these places and quite a lot of woodland plants get pollinated by flies and not by bees.

Flowers are not only places to find nectar and pollen but are also used by some flies as a place to find a mate, to lay their eggs or to take shelter.

The flowers that are pollinated by flies are typically:

• Pale and dull to dark brown or purple
• Sometimes flecked with translucent patches
• Putrid order, like rotting meat , carrion, dung, humus, sap and blood
• Nectar guides not present
• Produce pollen
• Flowers are funnel like or complex traps

Flies (Diptera) can be split into two main groups, the Nematocera and the Brachycera. Nematocera have elongated bodies and long, often feathery antennae. Midges, mosquitos and crane flies belong to this group. Brachycera have a more roundly proportioned body and short antennae and all the remaining flies such as hoverflies (Syrphidae), house flies (Muscidae), blow flies (Calliphoridae) and flesh flies (Sarcophagidae) belong to this latter group.

Flower pollination by a fly. An important group of flower-visiting flies are the root-maggot flies (Anthomyiidae), house flies (Muscidae) and Fanniidae (no common name). All are relatively small grey flies and they like to visit sweet-scented flowers. They also seem attracted to sweet-scented flowers with a tang of stale dung or urine smell.

Hoverflies (Syrphidae) are the most important family of flower visitors among flies. There are over 270 species of hoverflies in the UK and many are brightly coloured with yellow and black or red and black bodies. Many of the darker coloured species often look highly polished and some hoverflies are very furry and resemble bumblebees. Many hoverflies can be seen visiting flowers in sunny places but there are also quite a lot of species living in damp shady woodlands or at the woodland edge. Hoverflies get their name from the ability to remain stationary in the air which makes them easy to distinguish from wasps or bees. Most hoverflies visit flowers for nectar but some hoverflies are specialised pollen feeders and often visit flowers just to feed on the pollen.

Other flies commonly found on flowers are the blow flies (Calliphoridae) which are often metallic green or blue in colour and the large grey flesh flies (Sarcophagidae). Both can also be found feeding on carrion and excrement but will often visit flowers to feed on the nectar.

Dung flies (Scathophagidae) are predatory flies and often visit flowers to seek out prey. But many dung flies will also feed on the pollen and nectar of the flower.