The following is reprinted from Philip Rowley,s website: Fly Craft Angling with his permission.

Mired in a reputation born from movies such as Stand by Me and The African Queen, leeches are effective, as they are repulsive. Capable of reaching sizes in excess of 8 inches trout favor smaller leeches that are 3 inches in length or less. Knowledgeable anglers have found increasing success using leech patterns tied on hooks sized 10 and smaller. These baby leeches are lethal in the near shore shallows during the late fall.

After a heavy feast of chironomid pupa leeches are a favorite dessert. Like a natural cork trout use leeches to hold their heavy feed of chironomid pupa down. Nightfall is another prime leech opportunity. Primarily nocturnal leeches love to prowl under the cover of darkness making dusk prime time to knot a leech pattern onto the leader. Excitement awaits those who stay out past their bed times to fish well into the night especially during the dreaded summer doldrums. A stillwater staple offering year round appeal leeches are great candidates for early spring and late fall fishing. At these times trout are concentrated in the shallows often with barely enough water to cover their backs. In the fall small leech patterns presented on a floating line and 15 foot leader accounts for legions of trout. Recently anglers have begun using strike indicators as a method to suspend their leech patterns in the shallows so their patterns can be presented properly.

Most anglers favor leech patterns as a chuck it and chance it pattern because of the leeches active swimming habits. A large food item trout seldom turn their nose up at a leech undulating in open water. When fish are in an active mood leech patterns that are retrieved using either slow 12 inch or steady 4 inch pulls work like magic. During these active phases gaudy leech patterns draw trout from quite a distance. The jigging action of a bead head pattern is another trick of the trade for successful leech designs. If trout are fickle stick to somber patterns crept along with a slow methodical handtwist retrieve to imitate a leech meandering along the bottom. The horizontal presentation afforded by slow sinking, intermediate and Stillwater fly lines make these lines necessity for serious leech imitators.

The majority of popular leech patterns lean towards the darker colors of black or maroon. These color schemes offer a great silhouette and are patterns of choice for low light or evening fishing. Keep in mind that leeches come in a myriad of colors including brown, olive and green. On bright days the earth tones of a brown or the camouflaged mixture of a green and olive leech should not be overlooked.