When is the Hawthorn Fly most available to trout?

April–May, typically 12:00–16:00. It picks up from about 4°C, peaks around 12°C and tails off by 22°C.

What flies imitate the Hawthorn Fly?

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

How big is the Hawthorn Fly?

Adult stage: 12–14mm. That matches a #12–10 hook.

Terrestrial · Terrestrial

Hawthorn Fly

Bibio marci

Size

12–14mm

Hook size

#12–10

Hatch window

Season April–MayPeak time 12:00–16:00

Water temperature

12° peak

4°22°

How fish feed on it

Nothing about a beetle or an ant belongs in the water, which is rather the point — once it's in, it isn't getting out, and a trout that's spent all summer learning this doesn't need convincing twice. The takes tend to be confident and unhurried, especially along undercut banks and under overhanging branches where windfall has been landing for as long as the tree's been there.

Flies that imitate this

Black Gnat

Hawthorn

Bibio

Ecology

Rivers & stillwaterLimestone loughsLowland lochsReservoirsTolerates poor water

Where you'll find this

British IslesCommon
ScandinaviaCommon
Continental EuropeCommon
Atlantic fringeCommon
The AlpsOccasional
IberiaOccasional

Common Occasional

Identification

Bibio marci or St. Mark's fly is a fly from the family Bibionidae. Their common name comes from the fact that the adults usually emerge around St Mark's Day, 25 April.