Bibionid · Terrestrial insect
Black Gnat
Bibio johannis
Size
6–9mm
Hook size
#16–14
Hatch window
Season April–OctoberPeak time 11:00–17:00
Water temperature
13° peak
8°20°
Hatches from 8°C, peaking at 13°C, tailing off by 20°C.How fish feed on it
This one has no ascending pupa behind it either — a black gnat is a true fly of the bankside, not the water, and mating pairs caught out over the margins by a gust are the whole story. O'Reilly's account has them swarming near the surface in spring and again in autumn, thickest in the shade under overhanging trees on stillwaters and over the slower stretches on rivers, with blustery weather doing the damage: a mating pair, already clumsy, has no chance once the wind gets under it. Fish it small and dark — a size 16 or 18 is usually all the imitation needs to be.
Flies that imitate this
Black Gnat
Griffith's Gnat
Coch-y-bonddu
Ecology
Where you'll find this
- British IslesCommon
- Atlantic fringeOccasional
- ScandinaviaOccasional
- Continental EuropeOccasional
- The AlpsScarce
Common Occasional
Identification
Bibio johannis is a species of fly in the family Bibionidae. It is found in the Palearctic....