Britain's Hoverflies: A Field Guide - Revised and Updated Second Edition
312
Britain's Hoverflies: A Field Guide - Revised and Updated Second Edition
312eBookRevised and Updated Second Edition (Revised and Updated Second Edition)
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Overview
Britain's Hoverflies is a beautifully illustrated photographic field guide to the hoverflies of Britain, focusing on the species that can be most readily identified. It is the perfect companion for wildlife enthusiasts, professional ecologists and anyone else with an interest in this fascinating group of insects, and is designed to appeal to beginners and experts alike.
Accessible, authoritative and easy to use, this book contains hundreds of remarkable photographs of the various life stages of those species that can be identified by eye or with a magnifying glass, with coverage of at least one representative from each of the British genera. It also features an essential guide to the hoverfly tribes. Detailed species accounts summarize the species' status, highlight the key identification features, provide notes on behaviour and habitat requirements and include flight-period charts and up-to-date distribution maps. Sections on hoverfly biology, where and when to look for hoverflies, legislation and conservation, photographing hoverflies, recording hoverflies and gardening for hoverflies are also included.
This fully revised and updated second edition:
- Features more than 650 stunning colour photographs
- Provides detailed information for the 167 species that can be most readily identified, including at least one species from each of the 68 genera recorded in Britain
- Includes a complete list of the 283 hoverfly species recorded in Britain to date, with an indication of how difficult each is to identify
Product Details
| ISBN-13: | 9781400866021 |
|---|---|
| Publisher: | Princeton University Press |
| Publication date: | 04/13/2015 |
| Series: | WILDGuides of Britain & Europe , #112 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 312 |
| File size: | 67 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Read an Excerpt
Britain's Hoverflies
A Field Guide
By Stuart Ball, Roger Morris
PRINCETON UNIVERSITY PRESS
Copyright © 2015 Stuart Ball and Roger MorrisAll rights reserved.
ISBN: 978-1-4008-6602-1
CHAPTER 1
Hoverfly biology
Adults
The adult stage is what we normally see and think of as 'the hoverfly. They are relatively short-lived and survive for a few days to a few weeks. One mark-release-recapture exercise revealed that the large, black-and-white Great Pied Hoverfly Volucella pellucens can live for at least 35 days, although the average adult life-span was 12 days. Great Pied Hoverfly Volucella pellucens Recent mark-recapture studies of Hammerschmidtia ferruginea found the maximum adult lifespan to be 55 days. The primary function of the adult is to mate, disperse and lay eggs. Energy and protein are required to form the eggs. In the main, adult hoverflies obtain these by visiting flowers to obtain energy-giving nectar and protein-rich pollen. Most hoverflies lack specialised mouthparts, so prefer to visit flowers in which the nectar and pollen are exposed and easy to reach. White umbellifers, such as Hogweed, and members of the daisy family, such as thistles and knapweeds, are favourites.
One instantly recognisable genus of British hoverflies, Rhingia, is exceptional however, in having its mouthparts extended into a long snout, or rostrum. The rostrum has a groove on the underside into which the rather elongated proboscis fits. Consequently, it can visit flowers with a moderately deep tube, like Red Campion and Bluebell, to take advantage of a food source that is out of the reach of other hoverflies.
The closely related genera Xylota, Brachypalpoides and Chalcosyrphus tend not to visit flowers at all. Instead, they feed on honeydew, the sugary secretion of aphids, and pollen grains stuck to the leaf surface. They run over the surface of leaves, rapidly turning backwards and forwards in a very characteristic manner that makes them look like an ichneumon or spider-hunting wasp.
A number of smaller hoverflies, notably members of the tribes Bacchini (Melanostoma, Platycheirus), visit the flowers of wind pollinated plants such as plantains, grasses and sedges to obtain pollen. These plants provide a particularly rich food source through the production of great quantities of pollen.
Males of many hoverflies show some degree of territorial behaviour. They guard sunny spots by either hovering in a shaft of sunshine or sitting on a sunny leaf, from whence they dart out at other passing insects either to chase off a rival or to mate with a female. The same individual will return repeatedly to the same spot. Mark-release-recapture studies have also found that the same male of Volucella pellucens will return to hover in the same position along woodland rides on several successive days, indicating a strong and sophisticated level of territoriality.
The very noticeable high-pitched whine often heard in British woodlands on sunny Summer days is generated by thousands of male Syrphus species involved in territorial behaviour. In order to be ready to move at a moment's notice, they keep their wing muscles 'ticking over'. This causes the thorax to vibrate and this vibration is transmitted to the leaf surface, which acts like a sounding board.
Courtship is usually very brief. If the male encounters a female during his darting territorial flights, he grapples with her and, if accepted, they couple, either in flight or after falling onto vegetation. Mating usually lasts for a few minutes.
The small, honey-bee-like hoverfly Eristalis nemorum exhibits a more conspicuous courtship-related behaviour than most other hoverflies. A female is often seen feeding on a flower with a male hovering a few inches above her. It is not clear whether this is courtship behaviour or 'mate-guarding'. If a male has mated with a female, it is not unusual, across a range of insect groups, for him to then stand guard over her to stop other males mating with her before she has a chance to lay the eggs he has fertilised. This may be the case with E. nemorum but occasionally two or more males may be involved, jockeying for position over the female; this behaviour could therefore be a form of courtship. An interesting project for someone would be to investigate what is really going on!
Occasionally you may encounter a hoverfly with a distended abdomen with distinct pale whitish bands emerging between the segments. Such flies are usually dead and are firmly fixed to a plant; the genera Melanostoma and Platycheirus are particularly afflicted.
These have succumbed to a fungus that grows inside the insect and emerges between the body plates in order to release its spores. Mass occurrences of dead hoverflies attached to the undersides of umbellifer flowers or to grass stems are most frequently encountered in late Summer and early Autumn. Fungi that attack insects are referred to as 'entomophagous' and are one of the more noticeable causes of death amongst hoverflies.
Eggs
The ovipositor of female hoverflies consists of soft and flexible telescoped sections which, due to a complex arrangement of muscles and sensilla, has incredible sensitivity and manoeuvrability. It enables the fly to deposit eggs, singly or in small batches, very carefully and accurately, in a suitable place for the larvae to find food. Species whose larvae feed on aphids often lay eggs in or near aphid colonies. Those species with plant-feeding larvae usually lay eggs on particular host plants. Identifying the plant on which a female is egg-laying can, therefore, provide a useful clue to the identification of species within some genera (e.g. Cheilosa, Merodon, Eumerus).
Hoverfly eggs are usually somewhat elongate-oval in shape with one end wider than the other and often slightly curved. They are typically cream-coloured or pale yellow with a sculptured surface of fine pits and ridges or net-like patterns. These patterns can be distinctive and, potentially, used to identify a species, but very high magnification is required for them to be fully appreciated. When seen through a Scanning Electron Microscope the patterns are often quite beautiful. Larger species generally lay larger eggs; those of Volucella are around 2 mm in length, those of Syritta only 0-5 mm.
In the few cases where it has been observed, eggs hatch after quite a short period, typically no more than 5 days, but this is highly dependent upon temperature.
Larvae
Hoverfly larvae are typical of many dipteran larvae, being maggot-like, without legs or a head capsule. They are often somewhat wider at the rear end and narrow towards the head. Fly larvae usually have two prominent breathing tubes at the rear end: the posterior spiracles. In hoverflies, these are fused into a single structure: the posterior breathing tube. This is a characteristic of the hoverfly family which enables their larvae to be distinguished from most other fly larvae.
Larvae pass through three stages, or instars, during their growth. At the end of each stage they shed the outer skin so that the next stage can grow larger. The first two instars normally last just a few days. However, the third instar can last for weeks, months or even years, depending on the species. In many ways, the third instar larva is the hoverfly. This is the stage that does most of the feeding and its requirements largely determine the habitat and ecological importance of the species.
The ways in which hoverfly larvae live and feed are amazingly diverse and is reflected in their shapes and specialisations. The larvae of most British flies are poorly known and for some families they are virtually unknown. However, this is not true of hoverflies, since the larvae of about two thirds of the species have been described and the biology of around half is known in some detail. Keys to these species are included in Graham Rotheray's Colour Guide to Hoverfly Larvae (1993), but there are still plenty of species that require detailed study.
Aphid-feeding larvae
Hoverfly larvae are well known for feeding on aphids and are consequently regarded as 'gardener's friends'. In reality only about 40% of British species are predators of this type and aphids are not the only prey. A few species feed on a variety of other soft-bodied insects, including coccids and psyllids, and a few feed on other insect larvae. For example, the larvae of Xanthandrus comtus feed on gregarious micro-moth caterpillars and those of Parasyrphus nigritarsis feed on the larvae of leaf beetles on willows and Alder along streams and rivers.
Predatory hoverfly larvae usually have an extensible and rather mobile front part of the body which they use to probe for prey. They are blind, so rely upon a combination of chemical senses and touch to locate prey. Having located its prey, the hoverfly larva pierces the skin with long thin mouth hooks and sucks out the contents of its victim's body. They have rather sticky saliva which is used to help hold the prey in place whilst they do this. Finally, the empty husk is discarded. While doing this, the larva often rears up and lifts the aphid off the leaf. It is thought that this behaviour helps to prevent alarm pheromones released by the aphid reaching the rest of the colony. It may take a first instar larva several hours to deal with a single aphid, but a fully-grown larva can consume an aphid in a minute or two.
One of the most unusual features of predatory larvae is that they are coloured, unlike most other hoverfly larvae, which are pale yellowish-white. Being coloured helps to provide camouflage, which reduces the risk of predation when they are moving around on the surface of a plant in search of prey. Many such larvae are green, often with longitudinal stripes of white, yellowish or brown blotches to break up their outline. Some of the most striking patterns are found in Dasysyrphus.
These larvae feed at night on tree-dwelling aphids and rest on branches and trunks during the day. They have 'frilly edges' to break up their outline and patterns of reds, greys and browns that camouflage them perfectly against the bark. Another remarkable larva is that of Meligramma trianguliferum, which is a perfect bird-dropping mimic.
The larvae of the tribe Pipizini tend to specialise in feeding on aphids inside galls and leaf curls. The larvae of Heringia heringi, for example, are common in the galls on the stems of poplar leaves induced by the aphid Pemphigus. These larvae have less need of camouflage patterns because they spend much of their time hidden away inside galls – although some Pipizine larvae are green.
Larvae in the nests of ants
The larvae of a number of striking black-and-yellow hoverflies belonging to the genera Chrysotoxum, Doros and Xanthogramma are believed to feed on ant attended root aphids. The larvae of Pipizella occur in the same situation. This has been little studied: for example, it is not known how they get into an ants' nest; whether the female hoverfly enters the nest to lay eggs or whether a larva makes its own way in; and why the ants, which normally protect the aphids they farm from parasites and predators, do not kill the hoverfly larvae.
Doros profuges is listed as a priority species under the UK Biodiversity Action Plan and a good deal of work has been carried out to try and find out more about it. This work was prompted by a rather obscure 19th Century publication, which suggests that the larvae may be associated with ants nesting in wood, the most likely candidate being Lasius fuliginosus. However, the current research has had little success so far in understanding the ecology of this species.
The larvae of Microdon are highly specialised ant predators which feed on the eggs and brood of the host. The larvae are quite remarkable, being hemispherical and looking more like a woodlouse. Indeed, they were initially classified as molluscs in the 19th Century! The shape is probably an adaptation to protect them from the ants and they are heavily armoured to avoid bites and stings (see page 272).
Larvae in the nests of social wasps and bees
Volucella rank amongst our largest hoverflies and, with the exception of V. inflata, their larvae live in the nests of bees and wasps. V. bombylans larvae usually live in bumblebee nests, and the larvae of V. inanis, V. pellucens and V. zonaria live in the nests of social wasps. The larvae are mainly scavengers in the bottom of the nest cavity, feeding on dead workers and larvae, dropped food and the larvae of other insects that inhabit these nests. V. inanis, however, feeds directly on the wasp grubs and its larvae are flattened so that they can fit into a cell in the comb beside their victim. Larvae of V. pellucens have also been recorded feeding on moribund wasp larvae in the combs of abandoned wasps' nests late in the season.
Female Volucella have to enter the host nest to lay their eggs. Bumblebees sometimes react aggressively and it has been shown that female V. bombylans react to being stung by laying their eggs immediately. Observations of V. pellucens at nest entrances suggest that the wasps take no notice of them and they can freely enter and leave the nest.
Hoverfly larvae leave the host nest cavity in the early Autumn, when the nest is abandoned by the wasps or bumblebees. They pupate nearby: in soil if the nest is underground, or in debris in a tree hole in the case of tree-cavity nests. V. inanis quite often use wasp nests in buildings and consequently it is not uncommon for larvae to turn up in houses.
Plant-feeding larvae
Britain's largest genus of hoverflies, Cheilosia, together with Eumerus, Merodon and Portevinia, have larvae that feed in the roots, stems or leaves of plants. Cheilosia grossa and C. albipila are typical examples whose larvae mine the stems of thistles, particularly Marsh Thistle. Adults of both these species fly very early in the season (late March to April) and lay their eggs on thistle rosettes just as the plant starts to grow. The larvae of C. grossa may kill the growing point of the thistle when they start to feed, causing the plant to become multi-stemmed. Mature larvae mine the centre of the stem base, leaving a hollow tube. The larvae are fully grown by July or early August, at which time they exit the thistle by chewing a hole through the side of the stem and pupate in the soil surrounding the plant base.
Adults of Cheilosia grossa and C. albipila are often overlooked because they fly so early in the year. It is, therefore, much easier to record these species by searching for their larvae in thistle stems (see facing page). Mature larvae are relatively easy to tell apart because their posterior breathing tubes have characteristic shapes. Unlike adults, finding larvae is not dependent upon good weather, so a wet day in July can profitably be spent splitting thistle stems! This technique has shown that these species are much commoner and more widespread than records of adults suggest, especially in the uplands.
RecordingCheilosia albipilaandC. grossaby searching for larvae in thistles
The larvae of both species feed in the base of the stem of Marsh Thistle and those of C. grossa in other thistles such as Spear Thistle (but not in Creeping Thistle). They are easily found during May, June and July, or even August in the north, by splitting the base of thistle stems and looking for those that are hollowed out. Experience has shown that both species can be found in the same patch of thistles.
A good, hefty boot applied to the base of the stem will knock the plant over and open up the rosette. Insert a suitable implement and split the rosette and the base of the stem apart.
A clasp knife will do the job, but a small-bladed, sturdy gardening trowel or fork is probably better. It should be immediately obvious whether the plant has been tunnelled. An unaffected stem is filled with green, solid pith; a tunnelled stem is hollow and usually quite stained within by obvious deposits of brown frass. When you find a tunnel, split the stem upwards until you find the larva. Late in the season, you may find that the tunnel is no longer occupied – in which case it is worth a quick dig around the roots to look for mature larvae or puparia.
The larvae of these two species are quite easy to tell apart by the characteristic shapes of the posterior breathing tube (PBT). C. albipila is white and the PBT is parallel-sided and has a 'dagger point' projecting between the tips of the two fused hind spiracles. C. grossa is a dirty brown colour and the PBT is broad and blunt with a flange either side.
Other species of Cheilosia that occur in thistles are generally similar, but lack the diagnostic 'dagger point' or 'flanges'. Larvae of C. fraterna and C. proxima favour the more slender growth and side branches higher up on the plant, but little is known about others such as C. mutabilis and C. cynocephala (the latter of which is thought to be restricted to Musk Thistle). You may also find other insect larvae, such as caterpillars of the Frosted Orange moth Gortyna flavago.
(Continues...)
Excerpted from Britain's Hoverflies by Stuart Ball, Roger Morris. Copyright © 2015 Stuart Ball and Roger Morris. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents
- Frontmatter, pg. 1
- Contents, pg. 3
- Foreword, pg. 7
- Preface, pg. 9
- Introduction, pg. 10
- Is it a Hoverfly?, pg. 12
- Hoverfly biology, pg. 15
- Finding hoverflies, pg. 34
- Glossary, pg. 46
- Identifying hoverflies, pg. 49
- Bacchini, pg. 71
- Paragini, pg. 92
- Syrphini, pg. 94
- Callicerini, pg. 154
- Cheilosiini, pg. 158
- Chrysogastrini, pg. 180
- Eristalini, pg. 198
- Merodontini, pg. 220
- Pelecocerini, pg. 226
- Pipizini, pg. 228
- Sericomyiini, pg. 240
- Volucellini, pg. 244
- Xylotini, pg. 250
- Microdon, pg. 272
- List of British and Irish hoverflies, pg. 276
- Photographing hoverflies, pg. 285
- Collecting hoverflies, pg. 291
- Legislation and conservation, pg. 296
- Recording hoverflies, pg. 297
- Gardening for hoverflies, pg. 299
- Further reading and useful addresses, pg. 302
- Acknowledgements, pg. 304
- Photographic credits, pg. 305
- Index of scientific names, pg. 309