The St. Marks or hawthorn fly (Bibio marci) gets its name because the adults emerge around St Mark’s Day which is on the 25th April. The hawthorn fly is a fly (Diptera) in the family Bibionidae which is distributed across much of Europe, central Asia and north Africa. The fly is associated with a variety of, often wet but warm, habitats including hedgerows, woodland edges and rough grassland. They are hairy and completely black in colour, 12 – 14 mm in length, with milky white to smoky brown wings (8 – 12 mm in length). An additional distinguishing feature is their long trailing legs when they fly. While the males have a larger head and eyes this is unlikely to be of significance in a fly pattern.
The hawthorn fly is generally on the wing from mid-March through mid-May although there are records of occurrences in warmer Januaries. The peak occurrence is generally late April and early May. The males form large 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 small surface waters where the fish take full advantage of the bonanza. The adults live for about 1 week feeding on nectar and are important pollinators. The larval stage feeds on decaying organic matter and plant roots (often Poaceae) and hatch the following spring.
Flies that work well are:
- Foam hawthorn fly – size 12-14
- Classic hawthorn fly – size 12-14
- Leggy hawthorn fly -size 12
- Wet hawthorn fly – size 12
For the fly tyers some key patterns:
- Trout Fisherman Magazine pattern
Tight Lines
Greg