Golden hoverfly (Callicera spinolae)

KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderDiptera
FamilySyrphidae
GenusCallicera
SizeBody length: 15 mm
Wing length: 12 - 15 mm

Classified as Endangered in the UK.

The golden hoverfly is, by comparison with other members of its family, large. It is also one of the rarest and identification is not easy as it can be confused with another species of Callicera. The golden hoverfly also looks very similar to the common wasp, but can be distinguished by its antennae which are longer than the wasp's, and have white tips. They also have just one pair of wings whereas wasps have two pairs. The golden hoverfly has a body which is metallic bronze in colour with bands of golden hairs across its abdomen. The wings also darken slightly towards the tips.

Rare, even in western Europe, the golden hoverfly is mainly confined to East Anglia in its UK distribution, on three sites historically. However, it probably flies between sites readily, and a recent record from Hertfordshire suggests the species is migrating westward. It remains at only one of its former sites in the east of the region.

This species is associated with dead and dying trees, especially those that contain rotten wood. It is regarded as an 'indicator species', that is a species whose presence indicates the quality of a particular habitat, or micro-environment within a habitat, such as dead wood.

Hoverflies, unlike many other families of flying insects, enjoy a fairly good relationship with humans. This is in spite of the fact that many species practice mimicry and resemble wasps or bees. The sight of a hoverfly, hanging suspended above a flower, seems redolent of warm, summer days, with the still air full of drowsy buzzing. Hovering in still air requires a high expenditure of energy, and hoverflies visit flowers, primarily, to feed on nectar or, in some cases, pollen. Nectar consists largely of sugar and water, and many species of animals rely on it as a food source. Some hoverflies display a preference for a certain species of plant, and the golden hoverfly seems to favour ivy. A number of similar insects feed from ivy as well, and it can be difficult to distinguish them from visiting wasps and hornets.

Male hoverflies visit flowers for other purposes, too. They may be looking for females and it is thought that courtship flights take place, with the males hoping to mate. Having mated, female golden hoverflies search for trees in which to lay their eggs. They usually choose live, standing beech and ash trees, which have lost a branch and, through the activities of fungus and bacteria, developed a rot hole. A number of different types of animals use these rot holes, including birds such as owls, and they are an important part of the woodland ecology.

Hoverfly larvae are unusual among other insect grubs in having a 'tail', which consists of two fused breathing tubes. In most cases, such as with the golden hoverfly, this tail is short, but a few species that lay their eggs in water have larvae that have breathing apparatus several centimetres in length. These breathing tubes are vital to the grubs as the interiors of rot holes are frequently wet. The golden hoverfly larvae take two years to reach the pupation stage in their life-cycle. The adult flies emerge in September or October, unlike most other hoverflies which are on the wing in spring and summer. Just before hatching, the pupa moves to a drier part of the rot hole so the emerging adult hoverfly avoids getting wet. Tree holes can provide food and accommodation for many generations of hoverflies, so it is important to retain these features within a wood. All too frequently, trees which show signs of rot are removed by woodland managers.

The chief reason for the disappearance of this species seems to be the loss of old, rotten trees in woodland, either through windblow, old age or felling, perhaps as a result of a desire to 'tidy-up'. However, in common with much of western Europe, East Anglia has lost much of its natural woodland to agriculture and development. The remaining woodland cover has become fragmented and probably reduces the opportunities for the golden hoverfly to disperse and colonise new areas successfully. Within remaining woods, current forestry methods do not encourage the development of the sort of rot holes needed by the hoverfly. Even in a suitable wood, there is the risk that the available holes are not wet enough to be suitable for the hoverfly larvae.

The golden hoverfly is listed in the UK Biodiversity Action Plans and is included in English Nature's Species Recovery Programme. Essentially, the work to recover this species in the UK will concentrate on protecting its habitat and publicising the benefits of suitable woodland management. It is important, of course, to protect not just the broadleaved woodland itself, but encourage landowners and woodland managers to leave trees that have rot holes standing. It has also become popular in some areas to remove ivy from hedgerows and trees in the mistaken belief that it causes damage to the host tree. Ivy not only provides an important source of nectar for insects, but nesting cover for birds and food through its berries. Protecting ivy is another vital part of the recovery plan for the golden hoverfly. A project to provide artificial breeding sites is also being planned. This will involve fixing plastic bottles full of wet sawdust to trees in suitable woods to provide a suitable medium in which the hoverflies can lay their eggs.

As this species is found in Europe, this research will be published and made available to conservation organisations elsewhere. In this way, the lessons learned in the management of potential breeding sites in Britain may reverse the fortunes of this attractive insect throughout its range.

Information supplied by English Nature.

http://www.english-nature.org.uk