Flies: the forgotten pollinators

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 of them will visit flowers for pollen and nectar as well.

 

There are around 7000 known species of flies known in the UK (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.

Flower-visiting flies have large eyes to spot flowers

 

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.

Short-tongued flies are often attracted to yellow and white flowers or brown/dark purple flowers while longer-tongued flies are also visiting purple and blue flowers which often have more deeply seated nectar than flowers of other colours.

This hoverfly (Eristalis tenax) is attracted to the yellow dandelion flowers

 

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.

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.

Flies belonging to the Brachycera have a round body and short antennae

Mosquitos, crane flies and midges (Nematocera) are not very important pollinators due to their often small size and short mouth parts. Most visit flat or bowl-shaped flowers with well-exposed nectar which they can easily reach. Some eat pollen and especially mosquitos can be seen visiting flowers at night.

An interesting relationship exists between the small owl-midges (Psychodidae) and the common woodland plant lords and ladies (Arum maculatum). Lords and ladies flowers in May with a poker-shaped inflorescence called spadix. The male and female flowers are at the base of the spadix with a ring of hairs above which acts as an insect trap. The little owl-midges are attracted to the faecal odour and the higher temperature (up to 15 C higher than ambient temperature) of the spadix and get trapped under the ring of hairs. While trying to get out they are dusted with pollen from the male flowers (which are just under the ring of hairs) and once they escape carry the pollen to other plants where they pollinate the female flowers.

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.

 

The pretty Volucella bombylans mimics a bumblebee

Most hoverflies visit flowers for nectar but some hoverflies such as some Melanostoma spp., Syrphus spp. and Episyrphus balteatus (Marmalade hoverfly) are specialised pollen feeders and often visit flowers just to feed on the pollen.

Two Syrphus sp. hoverflies feeding on pollen in a Californian poppy flower

 

Hoverflies often like to visit open cup-shaped flowers or small tubular flowers with easily accessible nectar such as buttercups (Ranunculus spp.), anemones (Anemone spp.), potentillas (Potentilla spp.) and many flowers from the daisy family (Asteraceae) and carrot family (Apiaceae) such as ox-eye daisy (Leucanthemum vulgare), thistles (Cirsium spp.), dandelion (Taraxacum agg.), calendula (Calendula officinalis), fennel (Foeniculum vulgare) and wild carrot (Daucus carota). Pollen-eating hoverflies are also often visiting poppies such as corn poppy (Papaver rhoeas) and californian poppy (Eschscholzia californica) which produce no nectar but offer an abundance of pollen.

 

A pretty Volucella pellucens on a thistle flower

Another 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 such as meadowsweet (Filipendula ulmaria), rowan (Sorbus aucuparia), crap apple (Malus sylvestris), willows (Salix spp.), ladies bedstraw (Galium verum) and thrift (Armeria maritima). They also seem attracted to sweet-scented flowers with a tang of stale dung or urine smell such as cow parsley (Anthriscus sylvestris), sweet alyssum (Lobularia maritima) and oil-seed rape (Brassica napus).

The bee-flies (Bombyliidae) include some of the most highly specialised flower feeders among the flies and are often medium-sized hairy flies with a very long slender proboscis. They often visit relatively large long-tubed flowers such as primroses (Primula vulgaris), cowslip (Primula veris), honesty (Lunaria annua) and wallflowers (Erysimum cheiri). Similar to hoverflies, bee flies are able to remain stationary in the air and usually hover in front of flowers when feeding. Bee flies are highly-developed nectar feeders and move rapidly from flower to flower to drink nectar. As they are early-flying they can be important pollinators of early spring flowers.

A large bee fly (Bombylius major) visits forget-me-not flowers

Another interesting group of flies which visits flowers are the thick-headed flies (Conopidae). They have a long proboscis and like to visit small tubular flowers such as wild marjoram (Origanum vulgare) and flowers in the daisy family (Asteraceae) and carrot family (Apiaceae).

Tachinid flies (Tachinidae) are small bristly flies, some of them such as the relatively common Eriothrix rufomaculatus with a black and red body. The larvae of tachinid flies are internal parasites of other insects and arthropods but the adult flies are often found on flowers such as mint (Mentha spp.) and flowers from the daisy and carrot family.

A tachinid fly on a daisy flower

 

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. 

Blow flies like to visit open flowers such as fennel

 

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.

A dung fly is waiting for some prey to catch

There are many other flies which will visit flowers for feeding or other reasons but there is not enough space here to mention them all. All flower-visiting flies provide an important pollination service to many plants and should not be forgotten and overlooked.

Early spring butterflies

The fine and dry weather has brought out the early spring butterflies and you can see Brimstone, Small Tortoiseshell, Peacock and Comma butterflies basking in the sun or dancing over early spring flowers. These early butterflies have overwintered as adults in cellars, sheds, garages, between foliage or in other sheltered places and are waking up as soon as the temperature rises in late winter or early spring. The butterflies will drink nectar from all sorts of early spring flowers but they particularly like to feed on Aubrieta, ornamental cherries (Prunus spp.), Purple deadnettle (Lamium purpureum), Flowering currant (Ribes sanguineum), Dandelion (Taraxacum agg.),  Primrose (Primula vulgaris) and Cowslip (Primula veris). I have also seen many butterflies feeding on the flowers of the Indian plum tree (Oemleria cerasiformis) which is native to North America and can be grown in UK gardens.

The Comma (Polygonia c-album) is now quite a common sight in England and Wales and gets its name from a white mark on the underside of the wings which looks a bit like a comma (or a C, hence the scientific name). With closed wings the butterfly has excellent camouflage and resembles a withered leaf. The larvae (caterpillars) feed on nettles.

A Comma basking in the warm sunshine

Early butterflies often feed high up in flowering trees

A Comma drinking nectar from ornamental cherry flowers

Good to see is the white mark which gave the Comma its name

The Brimstone (Gonepteryx rhamni) is probably the earliest butterfly many people see, sometimes even flying in the middle of winter on a sunny mild day. The male butterfly is bright yellow and unmistakable. The female butterfly is much paler, more a whitish-green colour, which can sometimes be mistaken for a Large white butterfly. Brimstones often hibernate between foliage and the wings perfectly match the shape of a leaf when closed. The caterpillars feed on Alder buckthorn (Frangula alnus) and Buckthorn (Rhamnus cathartica).

A male Brimstone feeding on Flowering currant flowers

One of the most distinctive of all butterflies is probably the Peacock (Aglais io). The large fake-eyes on each wing are unmistakable and are designed to scare away potential predators such as mice or birds. The underside of the wings is nearly black and perfect camouflage when the butterfly is resting on a tree trunk. Peacocks can be found nearly all over the UK and are a common sight in gardens. The caterpillars feed on nettles.

The large fake-eyes can look quite threatening to a predator

Another very familiar early butterfly is the Small tortoiseshell (Aglais urticae) which is very common in gardens and allotments. The butterfly has usually 2 broods per year (only one in the far north) and the black and yellow caterpillars can be found on nettles.

Small tortoiseshell feeding on an ornamental cherry

 

You know that spring has really sprung when you see the pretty Orange tip (Anthocharis cardamines). This is one of the first species to emerge which has not overwintered as an adult. The male is white with the characteristic orange tips to the forewings; the female lacks these and looks more like a Green-veined or Small white in appearance. Often found on damp meadows, riverbanks, along hedgerows and at woodland margins where the primary larval food-plants (Cuckooflower, Cardamine pratensis and Garlic mustard, Alliaria petiolata) grow. You can entice them to your garden by planting some Cuckooflowers in a damp spot or by letting Garlic mustard grow wild under your hedge.

A pretty male Orange tip

More early spring flowers for pollinators

In addition to my earlier post "Early spring flowers for pollinators" I would like to introduce you to more pollinator-friendly early spring flowers, some of them, such as Hepatica, less known to gardeners in the UK but very popular on the continent. All of these flowers are hardy and many such as the Anemones are at home in deciduous woodlands in the wild where they attract early emerging pollinators such as bumblebee queens, solitary bees and hoverflies. Also lets not forget all the different Wild tulip species available to gardeners; most of them flower early and are great for pollinators.

Blue anemone and Balkan anemone (Anemone blanda and A. apennina)

Both plants look very similar and are native to southern Europe. The pretty blue, pink or white flowers and feathery leaves emerge from a tuberous rhizome in March. Plant the tubers in autumn in humus-rich, sandy and well-drained soil under deciduous trees or in a rock garden. The plants grow best in sun or part-shade. You can also buy ready-grown flowering plants in pots now in most garden centres which can be planted out in the garden. Anemone will spread quickly and form large clumps if planted in the right place.

 

A hoverfly (Eristalis pertinax) is visiting an Anemone flower

Wood anemone (Anemone nemorosa)

This native plant grows in deciduous woodlands and hedgerows and often forms large carpets of pretty white flowers in March. The plant is quite easy to naturalise in your garden under deciduous trees in humus-rich, moist but well-drained soil.

 

 

 Hepatica (Hepatica nobilis)

Similar-looking to Blue-and Balkan anemone but the leaves have a very distinctive three-lobed shape (resembling a human liver, hence the name Hepatica). The flowers can be blue or pink and emerge in March. In the wild Hepatica likes to grow in deciduous (especially beech) woodland on calcareous soil. This plant is the ideal plant if you garden on alkaline limestone-derived soil which can often be difficult to cultivate. But as long as you garden soil is not too acidic (if Rhododendrons grow well in your garden this plant is probably not for you) Hepatica will also grow in normal garden soil under deciduous trees.

The leaves are distinctly three-lobed

A pink Hepatica flower

Hollow root (Corydalis cava)

White and purple flowers emerge above feathery leaves from a hollow tuber in March or early April. Grows in decidious (often beech) woodland on calcareous soil in the wild and likes moist humus-rich ground. Looks pretty when planted together with Hepatica as both like similar places.

Spring snowflake (Leucojum vernum)

A very pretty spring bulb with large white dropping bell-shaped flowers with a green dot at the end of each petal which will flower in March. In the wild they grow in deciduous (often beech) woodland on calcareous soil and will form large carpets if conditions are suitable. Plant the bulbs in autumn in humus-rich moist (but well-drained) soil under deciduous trees.

 

Lesser celandine (Ficaria verna)

A pretty wildflower with relatively big yellow flowers which only open on mild sunny days. The plant is often growing in moist soil in sunny or half-shady places and can form big clumps in suitable conditions. Lesser celandine can be a bit invasive in a garden if conditions are suitable so best confine it to a wildlife corner. The flowers are an important food source for early pollinators such as emerging bumblebee queens, early solitary bees and hoverflies.

A Marmalade hoverfly (Episyrphus balteatus)

A buff-tailed bumblebee queen drinks nectar from a Lesser celandine flower

Pasque flower (Pulsatilla vulgaris)

This is a plant of calcareous grasslands and has strikingly pretty purple or pink bell-shaped flowers and feathery hairy leaves. The flowers open in late March or April and attract mostly early bumblebees. Plant in a sunny position on very well-drained neutral to alkaline soil. A good place for this plant is in a rock garden.

 

 

Grape hyacinths (Muscari spp.)

Bee flies like to visit Grape hyacinth flowers

The pale-blue to very dark-blue little bell shaped flowers, clustered tightly together, appear in early spring. The commonly planted Armenian grape hyacinth (Muscari armeniacum) can be a bit invasive in gardens (especially if planted in a rock garden) so if you do not want a large carpet of blue flowers in spring go for the less-invasive Grape hyacinths such as the pretty Azure grape hyacinth (Muscari azureum) or the larger Muscari latifolium. Plant the bulbs in autumn (or buy some flowering plants in pots now) in well-drained but not too fertile soil in a sunny or half-shady position.

A male Mason bee (Osmia bicornis) visiting the flowers

Wild tulips (Tulipa tarda, T. clusiana, T. sylvestris, T. humilis and others)

Wild tulips have smaller flowers than the big hybrid-tulips often seen in gardens and parks but are not less beautiful and often much easier to care for. Once planted wild tulips flower year after year without much maintenance whereas hybrid-tulips often fail to flower after only one year. Most wild tulips need a sunny place and well-drained light soil; a rock garden is often an ideal place for these little beauties. Flowers open as early as March and often attract solitary bees, bumblebees and hoverflies.

Tulipa humilis 'Little beauty'

Tulipa sylvestris

Tulipa clusiana close-up

A solitary bee in a Tulipa kaufmannia flower

Tulipa tarda

A hoverfly (Eristalis tenax) in a Tulipa kaufmannia flower

Tulipa humilis

A solitary bee (Andrena sp.)

A Garden bumblebee queen (Bombus hortorum)

If you are after pollinator-friendly plants for later in spring or early summer have a look here.