When is the Heather Fly most available to trout?

August–September, typically 12:00–17:00. It picks up from about 6°C, peaks around 14°C and tails off by 22°C.

What flies imitate the Heather Fly?

Bibio, Black Gnat, typically on a #12–10 hook.

How big is the Heather Fly?

Adult stage: 9–13mm. That matches a #12–10 hook.

Terrestrial · Terrestrial

Heather Fly

Bibio pomonae

Size

9–13mm

Hook size

#12–10

Hatch window

Season August–SeptemberPeak time 12:00–17:00

Water temperature

14° peak

6°22°

How fish feed on it

Hawthorn's sibling and out of the same mould — the same dangling-legged flight, the same dependence on warm air rather than warm water, the same fate once a gust catches a swarm over open water. But this one belongs to a different season and a different country: late summer, August into September, and heather moorland rather than lowland hedgerow — acidic loughs and upland spate rivers where Hawthorn barely reaches. Old accounts call it the Bloody Doctor, and it's worth having a Bibio or Black Gnat pattern ready on any warm, breezy August afternoon on western or Scottish moorland water, whether or not you've actually seen one on the wing yet.

Flies that imitate this

Bibio

Black Gnat

Ecology

Rivers & stillwaterPeaty loughsSpate riversTolerates poor water

Where you'll find this

British IslesCommon
Atlantic fringeOccasional
ScandinaviaOccasional
Continental EuropeOccasional
The AlpsScarce

Common Occasional

Identification

Bibio pomonae , common name red-thighed St Mark's fly or heather fly , is a species of flies (Diptera) belonging to the family Bibionidae.