Bog hoverfly: its diet, habitat and why its endangered

By Megan Shersby

Published: Tuesday, 03 January 2023 at 12:00 am

Many of us enjoy watching hoverflies as they dart around our gardens amongst the bees and wasps. Sometimes, it is hard to tell the difference as many hoverfly species mimic honeybees and bumblebees (there’s even a hoverfly that mimics a hornet!).

What are  hoverflies?

Hoverflies belong to the family Syrphidae which consists of over 250 species in the UK, some of which are incredibly rare. One of these remarkable rare species is the bog hoverfly Eristalis cryptarum.

Those who have been fortunate enough to see the bog hoverfly will be quick to tell you how difficult they are to find. Theoretically, they are an easy species to spot as they have bright orange legs, red gingery hairs on its thorax and yellow banding on their abdomen.

What is the bog hoverfly?

But the bog hoverfly is famously elusive and incredibly easy to disturb. I had to remain in the same position for at least three hours before I got to see a bog hoverfly for the first time. But they truly are a beautiful fly and it was well worth the wait.

As the name suggests, the bog hoverfly is found in wetter habitats, specifically along valley mires of Rhôs pastures (marshy grasslands that are grazed by wandering livestock).

Bog hoverfly diet

It has a few favourite flowers that they feed on too, such as devil’s-bit scabious, bog pimpernel, bog asphodel and marsh St John’s wort. And similar to its drone fly relatives in the Eristalis genus, the adults have a long flight season between May to late September.

How endangered is the bog hoverfly?

""
The boggy valley mires of Rhôs pastures are home to the aptly named bog hoverfly. © Catherine Mitson

The bog hoverfly has always been a scarce species, with previous records scattered across Devon, Cornwall, the heaths of Dorset and the New Forest. Sadly however, by the 1970’s it was only found on Dartmoor National Park in Devon, where it was last seen in 1978.

For a long time, the bog hoverfly wasn’t recorded at all, and it wasn’t until a Dipterists Forum field meeting in 1993 that it was found again on Dartmoor.

By 1999, the bog hoverfly was listed as a priority species on the UK Biodiversity Action Plan because of this obvious decline. Not only this, it has also been given a Critically Endangered status because of the restricted number of sites on Dartmoor we are able to find the bog hoverfly.

As with any species of conservation concern, an understanding of a species ecology is vital. Previous projects have brought to light specific locations on Dartmoor we are likely to find the bog hoverfly, the types of habitat that it prefers as well as its favourite wildflowers to feed on.

 

Catherine Mitson is an active volunteer for the invertebrate conservation charity Buglife and has recently completed a Master’s by Research with the University of Exeter studying the ecology and phylogeny of the bog hoverfly.

""