A Year of Hoverflies

What to see and do month by month...

Close-up photo of Episyrphus balteatus to aid identification Episyrphus balteatus
Although this is the coldest month of the year, it is certainly still possible to see hoverflies in Bedfordshire. Very conveniently for us, one of the best places to look is around buildings and in gardens. South-facing walls are always worth checking on sunny days, even when the air temperature is low. Amidst the basking bluebottles and other species, the honeybee-mimicking Drone-fly Eristalis tenax should stand out by its rather glossy appearance. Donít be deceived by the threatening pulsating abdomen, there is no sting involved here, just marvellous mimicry of insects that do possess one. Any blossom out now (for instance of viburnum or winter jasmine) will also attract tenax, as well as the few other species that overwinter as adults. Look out for the Marmalade Hoverfly Episyrphus balteatus, with the distinctive double bands on its abdomen.

This is a good time to make records of the less-commonly overwintering species: in Bedfordshire in recent years, they have included the slender Meliscaeva auricollis (with broad blackish "arrowheads" pointing up the centre of its grey-brown abdomen) and the chunky Scaeva selenitica (with u-shaped pale yellow crescents on a black background). Why not jot down what you find in your diary, or better still a dedicated notebook? You can then compare your results (with those of other observers if you wish) in this and future seasons. Quite apart from their intrinsic value, such records can potentially provide a useful measure of the rate of change in our climate, as warmer winters allow more species to survive.

Winter wears on, and as we at last notice the days beginning to lengthen, itís worth continuing to check sheltered spots and any flowers or blossom to be found. The likeliest hoverfly species to be present continues to be the Drone-fly - a "lazy honeybee" that shines in the winter sun. The Marmalade Hoverfly should also be in evidence on sunny days. In summer, individuals of this species tend to be bright yellow or orange, but now they may show much darker colours - including attractive blues - which are a result of cold temperatures during the development of the young insect. Any other hoverfly species seen will definitely be worthy of special note. Pay particular attention to the pattern of spots or bars you can see on the abdomen. These are key identification marks at any time of the year, but may well be unique in the field now, when there are few species about to confuse matters.

Even if there are no flies to be seen, time spent outdoors can still be put to good use in their study. For instance, this is a good month to take note of sheltered blackthorn bushes, large clumps of ivy, trees with discolorations caused by flowing sap, and lines of horse chestnut trees in suburban areas. In later months, some good hoverflies may be found in these places, as we will see. If the weather is grim, this is a great time to do some homework. Committing to memory a few basic details about the structure of hoverflies, and the broad groups into which they fall, will do wonders in helping you make sense of the different species when you are busy with them in a few weeks time. What better occupation for the naturalist who needs a good excuse not to venture out into the rain and cold!

Close-up photo of Eristalis pertinax to aid identification Eristalis pertinax
This is the crossover month, for hoverflies as for many other creatures in our county. In the first two weeks or so, the only species in evidence are likely to be those that have survived the winter as adults.

But when the first days of true spring arrive, they are joined by newcomers that have just emerged as fresh adults. The earliest of these may well be Eristalis pertinax, a close relative of the Drone-fly. It is about the same size, but with obvious light areas on slimmer hind legs, and with distinctive pale front feet. As a powerful hoverer, the first sighting may be of a male, several feet up, staking out a territory in some sheltered corner of the garden. When he lands, the abdomen looks rather cone-shaped or pointed, unlike the blunter Drone-fly.

Willow and hazel catkins provide a welcome early supply of food for several species, including in the genus Syrphus. You will need good, often captive, views to distinguish between the three common species in the genus, and many records will have to go down as Syrphus sp.

Close-up photo of a Syrphus to aid identification Syrphus sp.
Now also, two smaller, slimmer species make their first appearance, though both will be very common later in the year. Platycheirus albimanus has a shining abdomen - black and bronze in the male, black and silver in the female. As with many other species in this large genus, the male has distinctive broad front feet, in this case rather pale. The similar-sized Melanostoma scalare has an orange and black abdomen, in the male longish and swelling slightly towards the tip. If you havenít done so already, now is the time to finalise your solo or group expedition plans for the coming weeks. Of all the seasons, spring comes and goes the quickest: set aside some time to enjoy the natural wonders, and donít miss out this year!
It can be hard to believe when the showers are falling, but there are a number of insect species that favour this month especially. The secret to seeing early spring hoverflies is to find sheltered places with a supply of food, and to be there when the sun is out, even if that happens only briefly. One of the most productive places to be is in front of a blossoming blackthorn bush. If the wind is blowing, choose bushes well protected from it, perhaps along a ride in a wood. Among the hoverflies that especially like blackthorn, a striking species is the first bumblebee mimic of the year, Criorhina ranunculi. This large and furry black hoverfly occurs in both red-tailed and white-tailed forms. Quite a contrast is provided by the two sexes in the small species Melangyna quadrimaculata: the male has an unusual pattern of four small spots on the abdomen, and the female is all dark. Other species that love blackthorn include the large-spotted Parasyrphus punctulatus (which may be very numerous around the blossom), and Epistrophe eligans, a slim, but particularly bright and shiny mimic of a honeybee.

Close-up photo of Helophilus pendulus to aid identification Helophilus pendulus
Even if not many flies are about, standing in front of a frothy blackthorn bush with your back to the sun is not a bad place to be. However, this could be the first time in the year that you have to explain to other people what exactly you are doing! An alternative strategy is to move on, and look for some yellow flowers. Coltsfoot, marsh marigold and the first buttercups are always good places to seek hoverflies. Early customers could include Helophilus pendulus, whose vertically-striped thorax has caused some hoverfly-enthusiasts to label it the Footballer. Now is also the time to get acquainted with the large genus Cheilosia, members of which really love buttercups, often getting smothered in yellow pollen. There is some bad news: most species in the genus are black. The good news is that several are still quite easy to identify, and, for people who like a challenge, almost all can be worked out with patience and a hand lens.

April is a good time to check the latest publications, or this website, for BNHS events, and make plans to come along. You will have the chance to contribute and to learn about hoverflies and very much else besides.

Close-up photo of Leucozona lucorum to aid identification Leucozona lucorum
Things are really starting to buzz! Near the beginning of the month, several species of hoverfly will appear for the first time in the year. Among them is the very handsome Leucozona lucorum, with a foxy-red thorax, black and white abdomen and jet-black wing patches. It can be found in many habitats, from woodlands to gardens, and is hard to confuse with anything else. In the hedgerows, hawthorn blossom takes over from blackthorn, and is equally as rich in interesting hoverfly species. This month, too, the bluebell woods should be looking their best - but not every bulb will have produced a flower. Instead, something very different may have emerged, in the shape of an adult Merodon equestris - the Large or Greater Bulb-fly. Domesticated bulbs are not immune, and the gardeners among you may well see this species if you have cultivated narcissi, for instance. Forgive it if you can, for it is both attractive to look at, and very entertaining. It is a bumblebee mimic and comes in several colour forms from black to buff, often with broad black bands. It is great fun to watch the males zooming along the flower beds and deliberately ramming each other - or even bumblebees - in what is presumably territorial behaviour.

Close-up photo of Volucella bombylans to aid identification Volucella bombylans

Close-up photo of Volucella bombylans to aid identification Volucella bombylans var. plumata
Another bee mimic is on the wing now, but one with a very different life history. Volucella bombylans grows up in the nests of bees and wasps, scavenging on waste, even feeding on the young brood, and somehow emerging unstung. In southern England, the adults come in two colour forms, one black with a red tail, and one black and yellow, with a white tail. They look remarkably like bumblebees, but of course have just two wings (which are also well marked with black), and they spend more time sitting quietly than any bee. They are common in many habitats, and often come into gardens.

However, to see the next species, you will need to go to a wood - and not just any wood. At the end of the month, the wild garlic or ramsons is in flower in some of Bedfordshireís woods, and with it you should find a real specialist hoverfly, Portevinia maculata, the larvae of which feed on the bulbs of this plant and nothing else. The adults are very distinctive, black with rather faint greyish spots in pairs on the abdomen, and bright orange antennae. There is nothing else like them in the British Isles, but on the continent there is a species of Cheilosia which looks very similar, and feeds on ramsons. What can be going on there?

This is the best month of the year for hoverflies in all their great variety. For the enthusiast, there will not be enough hours, even in these long days, to see all that there is to be seen. As in all fields of natural history, however, anyone can make interesting observations, and here are a few special things to look out for this month. If, earlier in the year, you noted horse chestnut trees in suburban areas, now is the time to revisit them to look for one hoverfly in particular. Brachyopa insensilis is not interested in the flowers (which are now over and well on their way to conkerhood), but in the sap running from wounds on the tree, and staining the bark a darker colour. It is in this sap that the fly lays its eggs, and the larvae feed on it. The adult fly is distinctly odd-looking for a hoverfly. Mostly orangey in colouration, and with a grey thorax, it looks rather like some of our less-lovable flies, but a closer inspection shows the clean and non-bristly look of a proper hoverfly. Once thought of as a rural dweller, this species is being noted more and more often in residential streets and town parks, so keep an eye out for it sitting inconspicuously on the chestnut trunks there.

Close-up photo of Volucella pellucens to aid identification Volucella pellucens
Sap-runs on any type of tree are always worth checking for hoverflies; more species of Brachyopa may be present, and other hoverflies which utilise sap in this way include the shining Ferdinandea cuprea, and the large and handsome Volucella inflata.

If you fail with sap runs (and they are rather a challenge), you may feel like something a bit easier. If so, try a good-sized patch of bramble, now at the peak of flowering. Legions of insects are attracted to the blossom, and among the butterflies, beetles and bees, there are almost certain to be hoverflies present. Feeding on a woodland flower or hovering high in a patch of sunlight, may be one of our most distinctive insects, Volucella pellucens, the sun shining through the large white patches on its black abdomen.

Close-up photo of Scaeva pyrastri to aid identification Scaeva pyrastri
The hoverfly spectacle continues, with new species continuing to appear on the scene. This is a good month for Scaeva pyrastri, a large and striking species with broad white, somewhat u-shaped marks on its black abdomen. As the month progresses, if the weather is particularly hot and dry, hoverfly numbers may drop off markedly. Conversely, this is often the month when large gatherings of a few species of hoverfly may be experienced.

The genus Syrphus can be very numerous, with several on a single plant, or even bloom. There are three common species, all rather similar, especially the males. The female Syrphus ribesii is the easiest to distinguish, with hind legs that are entirely yellow, except at the very top. They are probably most peopleís idea of what a hoverfly should look like, definitely yellow and black, and given to persistent hovering.

Close-up photo of Syrphus ribesii to aid identification Syrphus ribesii
However, the real "invasion" species is most likely to be our old friend the Marmalade Fly, which regularly makes the newspapers for driving people out of the picnic sites and off the beaches. When we read these reports, we may be tempted to smile, for we know that any fear of being stung or bitten by these creatures is totally unfounded. However, even a keen naturalist might draw the line at having to extract flies from his or her holiday ice-cream or pint of beer! Although such invasions are often said to come from continental Europe, and perhaps some do, it is quite possible that these are in fact mostly British insects, arising from innumerable larvae that have fattened on aphids in our cereal fields, and are now, as adults, concentrated at the coast by their unwillingness to cross the sea. Whether at the coast, in the countryside or in the garden, the variation in population size from year to year, and the steepness of the rise and subsequent fall in numbers, may show some interesting patterns. You might like to try a series of counts on a measured stretch of flower bed or quiet road verge over a few days this month and make some notes, with a view to repeating the exercise next year.
Large numbers of some species may still be obvious at the beginning of the month, but in the next few weeks the drop in the numbers of species and individuals seen will probably begin to be obvious. By way of compensation, among the late summer hoverflies are some of the most spectacular in Britain - in particular the two large Volucella species. Volucella inanis is somewhat the smaller of the two (about the size of a common wasp, though rather stouter) and bright yellow, with two clear black bands on the upper abdomen. Volucella zonaria is the largest of our hoverflies, approaching the size of a hornet, and clearly mimicking that species, with dark orange and red-brown markings, the brown extending out onto the wings. Both flies come readily into our gardens and can be found, for instance, on buddleia and ice-plant (Sedum), alongside the bees and butterflies. A few years ago, such things would have been thought impossible in Bedfordshire, with the two species confined to the far south and southeast of England, and the area around London. Now, however, both are expanding their range northwards. V. inanis is the more frequent in our county at present, but perhaps zonaria will catch up in numbers. If you see either species, check it carefully, make a written note, and pass details to the Recorder or to the national Hoverfly Recording Scheme. In this way, the spread of both species (which may be linked to climate change) can be usefully monitored.
Close-up photo of Epistrophe grossulariae to aid identification Epistrophe grossulariae
The weather this month is often beautiful, of course, and there are still plenty of opportunities to find hoverfly species that have so far evaded detection this year. Among these might well be the golden-haired Epistrophe grossulariae, a species which often keeps its wings vibrating as it touches down on a flower to feed. One of the very best places to hunt for hoverflies is ivy, many plants of which will now be in full flower. Straightforward to find should be various species of Eristalis and Syrphus, as well as Helophilus pendulus and the chunky greenish-gold Myathropa florea. However, a great prize is possible: the extremely rare Callicera spinolae favours ivy flowers in autumn. It occurs in one of its very few British localities, not far over the county border in south Cambridgeshire, and (who knows?) it may live in one of Bedfordshireís ancient woodlands or long-established parks. Fittingly for such a rare creature, it stands out from the crowd, having long, angled antennae, clearly tipped with white, and golden bands of hairs across a shining abdomen.
Ivy is still flowering in the woods, and in the garden Michaelmas Daisy is likely to be a major attraction to hoverflies. There may well be up to four species of Eristalis present, and itís a realistic challenge to identify them all without catching them. On the larger species, check the legs: tenax has black hind-legs, with a hairy thickening where the pollen-basket would be on a honeybee (another example of the fine mimicry displayed by this species). E. pertinax has pied hind legs, and they are rather slender. On the smaller species, arbustorum has a distinctive unmarked face, with a "thatch" of pale hairs: it has an oblong brown mark (or "stigma") on the leading edge of the wing. E. interruptus has a dark stripe down its face, and a short, rather square, stigma.

If the identification challenge still seems a bit steep, why not try photographing them? With lower temperatures and food rather concentrated, hoverflies are less easily disturbed, allowing a close approach. If you are an experienced photographer, you will know about macro lenses, the depth of field challenge and the problems of camera-shake at low shutter speeds. If you are not, grab a digital camera, go out and snap away as many times as you can; itís surprising how many acceptable pictures will result, and certainly some will be good enough to identify tricky species. You can easily keep the better shots, and delete the others, making room again on your memory card. Of course, you can easily share your pictures with others, checking identifications and submitting your records at the same time.

Close-up photo of Sphaerophoria scripta to aid identification Sphaerophoria scripta
At the beginning of the month, in a normal year, there may well be eight or ten species of hoverfly still to be seen, with flowers as ever being the best place to look. Among them will be the last of the summer species, such as Sphaerophoria scripta, the males of which are distinguished by a very long abdomen that stretches beyond the closed wing-tips, as well as the commoner Platycheirus and Syrphus species. The last fly of the black-and-yellow genus Eupeodes is likely to be seen about now, and will probably be E. luniger. As with migrant birds, it is always more of a challenge to record the last individual than the first, so, as often in the year, it is worth making a written note of what hoverflies you see as you see them: you will then easily be able to determine when individual species have dropped out.

Close-up photo of Eupeodes luniger to aid identification Eupeodes luniger
How do these summer flies leave the scene? Is it that they are unable to survive the first spell of really cold weather; or do they simply come to the end of their natural lifespan and die, not to be replaced until next year? The answers to such question are by no means always clear, and may well vary between species. Also, as our climate gradually warms, the situation may change. The life histories of many hoverflies still await elucidation; do they spend the winter as eggs, larvae, pupae or adults? Perhaps some have mixed strategies (as is the case with a few butterflies). Amateur naturalists can of course contribute greatly to the understanding of such matters.
There are now very few flowers still blooming in the countryside, though the occasional fresh hogweed (always a good plant for hoverflies) is a welcome exception, and still merits checking for late individuals. In the garden, whatever colour remains will on sunny days be visited by the tough customers preparing to go through the winter. If youíve been watching since January, it will come as no surprise to you that Marmalade and Drone are the most likely to put in an appearance. It would be an interesting exercise to check each individual and note its sex: this is easy enough as, in both species, the eyes of males touch on the top of the head, those of females do not. Supposedly, more females survive the winter than males, but is this true, and if so, what are the differences in proportion between the sexes?

If you donít know what Christmas present to ask for, you could ask someone to buy you a book about hoverflies, or spend a gift token or some cash on one (Here are some suggestions). Other presents for the hoverfly enthusiast might include a hand-lens for close-up views, a nest of clear-bottomed card boxes, or a butterfly net (a white one is best for flies, and dark insects in general). Suppliers of these, and other items of gear, include Watkins and Doncaster, Anglian Lepidopterist Supplies, and Alana Ecology; all have helpful websites. If you havenít done so already, now may be a convenient time to get together your wildlife records for the year and send them to the relevant County Recorders: the Hoverfly Recorder would certainly be delighted to receive any records you have even of the commonest species. Why not do it over the holiday: it makes a break from the Christmas telly, and will call to mind summer days, both gone and to come. A Merry Christmas and a Happy New Year to you all!

John O'Sullivan

Bedfordshire County Hoverfly Recorder