Grannom sedges are prolific in running water nearly everywhere in trout country. On many waters the Mother’s Day Caddis hatch is the first big hatch of the season that gets trout keyed to selective.
Grannom are a cased caddis, the case square in cross-section. Trout eat the cased larvae when they can get them, & these are important as imitation on some streams, but the emerging pupae are, by far, the most important stage of this insect. During emergence, trout consume the pupae almost exclusively.
On my home water, true to their colloquial name, grannom season usually begins during the week of Mother’s Day, continuing until about the second week of June when they diminish, overtaken by the slightly larger spotted sedge that dominate the summer hatches.
Grannom adults are generally #16, with dark-brown to black bodies & light brownish-gray wings with faint mottling. Pupae are a size larger than adults, the abdomen color ranging from pale olive, through various shades of olive to bright green, & pinkish-brown to dark brown through the thorax area & wing holsters.
Grannom are uniform in size & when trout are keyed on them it is important that the imitation be exactly the right size. A soft-hackle spider provides a good profile of the emerging pupae. As color varies within the same population, a perfect color match isn’t important, though, so that my imitation stands out (without being too intrusive) among the bazillion naturals it’s competing against for the trout’s attention, I like to add some brightness through the abdomen portion of the fly – a bright green or reflective material.
As the season progresses & emergence slows down, trout will turn to eating more adult sedges, including drowned egg-layers. So it’s a good idea to carry more than one fly pattern for grannom.
A swung presentation works well with grannom. Activate the pupa with short 3-inch pulls or by pumping the rod as the fly swings under tension. If presenting a drowned adult pattern, swing it dead-drift. If there are visibly feeding trout, I position 45 degrees upstream of the target & concentrate on that portion of the swing between 90 degrees (straight out) & 45 degrees, that portion of the swing wherein the fly is pretty much dead-drifting. If nothing is showing on top I’ll fish two pupa with a sink-tip or on a long fluorocarbon leader.
Grannom sedges emerge midday through early evening, with egg-laying flights simultaneous. Here are a few of my current favorites for meeting them:
Hook: #14 ~ Thread: brown ~ Hackle: partridge ~ Rib: 2 strands of olive midge flash, twisted & wound as a rib ~ Body: olive rabbit with thorax of red-brown antron 
Hook: #14 ~ Thread: brown ~ Hackle: brahma hen or brown partridge ~ Rib: fine silver wire ~ Body: 4 strands of olive or pearl midge flash, twisted, & thorax of hares mask ~ Shroud: small pinch of Hareline Shrimp Pink UV Dub ~ Top with 2 gadwall flank fibers before winding the hackle
Drowned Egg-Layer ~ Hook: #16 ~ Thread: black ~ Hackle: partridge ~ Egg Sack: highlander green UNI yarn ~ Body: 3 strands of black midge flash, twisted, & thorax of dark brown dubbing
Partridge & Peacock ~ #16 (if tying on short-shank, caddis-style hooks, use a #14 hook) ~ egg sacks on this one are optional, the traditional Partridge & Peacock is reliable when trout are taking adult grannoms
