The Golden hoverfly (Callicera spinolae) is a rare species of ancient woodland and parkland in the south east of England. The larvae develop in wet rot holes so the hoverfly prefers old trees with snags or a complex structure of branches, which is more likely to produce the right microhabitat. The Golden hoverfly may be able to breed in a variety of different trees but it shows a clear preference for beech, horse chestnut and ash. Trees that have been pollarded are more likely to have rot holes. The Golden hoverfly avoids oak, even though this probably has a good structure, and is unlikely to use conifers. As the adults are active in September and October the hoverfly also likes sites with ivy, as this is one of the plants offering pollen and nectar later in the year.
|Golden hoverfly (Callicera spinolae) © Rob Garrod|
The adult hoverflies are large and furry with long black antennae that are white at the tip. From a distance they might be mistaken for social wasps, which also visit ivy flowers at this time of year, but with a clear view they should be unmistakeable. At this time of year the adults will feed and mate, then the female hoverfly will search for rot holes where she can lay her eggs. The larvae grow within the woody debris of the rot hole where they feed on bacteria and other microbes. They spend the winter as a larva and keep developing until the late summer of the following year, when they will pupate and then turn into an adult hoverfly.
The best chances of seeing this hoverfly are watching for adults visiting ivy flowers within the vicinity of ancient trees. Sightings are uncommon, however; the Golden hoverfly has only been seen at four locations in the past ten years. It’s possible Golden hoverflies spend much of their time in the tree canopy, and they may be under-recorded if they do not come close to ground level very often. The larva is distinctive and it is possible to identify them in rot holes, so other survey methods are possible.
Two closely related hoverflies that also breed in rot holes are Callicera rufa and Callicera aurata. Both these species are active from June to August so appear earlier than the Golden hoverfly. Callicera rufa has red hair rather than golden, and lives in the highland pine forests. Odd sightings of C. rufa have been made in England recently, and these are probably flies travelling north from the continent. Callicera aurata has less hair than the other two species and looks more brassy. This species can turn up in towns as well as in old woodlands, but despite appearing to have broad habitat requirements it is an uncommon hoverfly.