The heather fly (Bibio pomonae), sometimes referred to as the red-thighed St. Marks fly, is a fly (Diptera) in the family Bibionidae which is distributed across much of Europe and northern Asia. In southern Europe it is restricted to higher altitudes. The fly is associated with a variety of habitats including hedgerows, woodland edges, moorland, birch forest and wetlands. In the UK they are often associated with heathland and being the most cold-hardy bibionid may be found at altitudes of up to 1100 m. They are shiny black in colour, 10 – 13 mm in length, with clear to milky white wings (8 – 12 mm in length). An additional distinguishing feature is their long trailing legs when they fly and their deep crimson red femurs. While the males have a large head and flattened abdomen and the females small heads and pointed abdomen this is unlikely to be of significance in a fly pattern. While some authors will suggest that the need for red legs is not required, I would not agree with that. While fishing at llyn gamallt lake in late August (see post) I had two foam flies on my three fly cast, however, one of the flies was supplied with orange legs when I bought it online and it was rejected the whole day.
The heather fly is generally on the wing from April through October although there are records of occurrence in warmer Januaries. The first occurrences typically coincide with the flight time of the St. Marks fly in April/May while the primary flight time is July through September with the dominant peak typically in August.
The adults feed on nectar, often heather. The larval stage feeds on dead leaves, decaying organic matter and grass roots (Poaceae). Mass swarms/aggregations do occur in some years while the adults may be almost absent in others suggesting a semi-voltine life cycle. Recent literature which documents annual surveys of brown trout stomach contents suggests that in Norway mass aggregations of the heather fly occur every third year which may suggest that the larvae take three years to develop in that country. These mass aggregations may be offset and occur in different years in different regions. It has also been noted in Norway that the heather fly has altered its range, both spatially and altitudinally, possibly in response to climate change. The males form swarms and hover (fly up and down) between ~1 and 3 m height seeking to attract the females sitting on nearby vegetation. They aren’t the best flyers and get blown onto the small surface waters where the fish take full advantage of the bonanza.
Three flies that work well are:
- Foam heather fly – size 14
- Classic bibio fly – size 14
- Leggy heather fly -size 14
For the fly tyers:
Tight Lines
Greg