American Grannom (Brachycentridae)
Brachycentrus (Grannom). This is the most common genus found in most trout streams. Typically found in moderate to fast riffle areas attached to rocks and cobble. Abundant in small streams to large rivers.
The larvae, though cased, often become available to trout due to their common occurrence in stream drift and an unusual rappelling behavior. These Caddis drift in large numbers during the day. This activity makes them readily available to feeding trout. Gary LaFontaine in his book Caddisflies (1981) refers to the rappelling activity of grannom larvae: the larvae moved downstream by attaching an anchor line of silk to a rock. Letting go of the rock, the silk line held them in the current. By lengthening the line they moved downstream to another rock. LaFontaine further refers to fishing with great success when using a weighted cased larva pattern on a white colored leader to imitate this behavior.
When mature, the larvae often congregate in dense colonies in moderate currents. This results in concentrated areas of pupal emergence.
By opening a case with tweezers, the pupa can be removed and the color and size accurately determined. The maturity of the pupa can be assessed from the color of the wingpads: a mature pupa’s will be dark brown (almost black). When mature pupae are found you can expect to have good fishing with pupal patterns.
Most brachycentrid pupae do not emerge as quickly as many other caddis pupae. After cutting out of the larval case, they drift along the bottom for several feet, then start swimming towards the surface. It can take up to thirty minutes for the adult to emerge once the pupa reaches the surface film. This obviously presents an excellent opportunity for trout to feed on pupae drifting near the surface
Once free of the pupal shuck, the adults fly quickly to streamside vegetation where mating occurs after several days. Gravid females then return to the water in the afternoon or evening to lay their eggs. This presents the next excellent opportunity for fish and fishermen.
Most females flop on the surface to release their eggs. Some dive underwater. In both cases they drift quietly compared to the active fluttering flights of other adult caddis. During heavy egg-laying flights, hundreds of spent females will be drifting in or just under the surface film, and they present the perfect opportunity for a dead-drifted low-riding pattern. Hatches of brachycentrids can occur anytime from late March to Early October.