Black Fly

Scientific Name: order Diptera, family Simuliidae

Black flies are the most important trout food that nobody imitates. Note: this doesn't say black flies are the most important trout food--just the most important one that nobody bothers to tie flies for.

Black fly larvae are abundant in many running water habitats. They hold on tightly to rocky substrates. Pupation occurs underwater, and the fully-formed adult rises to the surface encased in a silvery bubble of gas. That bubble keeps their wings dry, so black fly adults emerge at the surface and instantly fly away. For this reason, you never see any rise forms during a hatch.

The best fly fishing tactic is to dead-drift a larva pattern through quick flowing, rocky habitat deep enough to hold trout; use tight line nymphing tactics to present a rising adult. You can also cast adult patterns where riffle water starts to slow at the head of a shallow run, but nymphing with a larva pattern is more productive.

You are not likely to find any imitations in a fly shop. However, there is an excellent two-part article on black flies and their imitations in the Westfly archives; see the sidebar for the link.


LARVA COLOR: Smoky gray, dirty yellow, creamish, or black

PUPA SIZE: 3-7 mm (1/8 to 1/4 in)

PUPA COLOR: Silvery case over black adult

ADULT SIZE: 3-7 mm (1/8 to 1/4 in)


OTHER CHARACTERISTICS: Back third of larva is much thicker than front