The American Grannom (Genus Brachycentrus ) Is a Springtime Gem

Written by: Ted Fauceglia

Larvae of Brachycentridae family are case-builders, creating chimney-shaped homes.
Photo by Ted Fauceglia

[Editor’s note: Ted Fauceglia is the country’s foremost photographer of aquatic insects, and he wrote the “Natural Reflections” column in each issue of American Angler for many years. Ted is also an FFI Certified Casting Instructor, the author of Mayflies (2004), and he has provided the bug and fly-pattern photography for dozens of books. He has graciously allowed us to republish some of his columns, and we will be sharing Ted’s incredible images and fly-fishing knowledge every month.]

Unlike the mystical status that we fly fishers have ascribed to mayflies and their hatches, the caddisfly has received little of the same reverence. Classically speaking, the elegance of mayflies and the art of fly fishing are inextricably linked. To some, catching trout rising to mayfly duns represents the highest and most noble of piscatorial pursuits with a fly rod. Conversely, and for reasons I’ve never understood, caddisflies have been relegated to a secondary position on our aesthetic scale of aquatic insects.

Perhaps it’s because of their worm-like larva stage or their moth-like adult stage. Who knows why? But the truth is that, despite the differences in our perception of the two insects, as a continuous food source for trout, caddisflies easily equal and probably surpass mayflies in importance.

More than 1,200 species of caddisflies inhabit the waters of North America. Many of them share the same habitat and live in close proximity to mayfly nymphs. However, unlike the free-living mayfly nymph, most species of caddisflies construct small tubular habitats in which they live. The building materials of the cases vary with the individual species; some species use sand or pebbles, others use bits of leaf debris, while other larger species use small sticks. Some species don’t build cases at all. Instead, they weave intricate, silken nets. Other species are free-living, like mayfly nymphs.

Caddisfly hatches occur from April through October in both the East and the West. Members of the Brachycentridae family are among the first and most prolific hatches to occur. In the East, Brachycentrus numerous, (a.k.a. the American grannom) appears around the third week in April, just about the same time the Hendrickson hatches begin.

Caddisflies have a complete life cycle, consisting of an egg, larva, pupa, and adult. In typical caddisfly style, grannom larvae (the-worm like stage) build and live in cases. Unlike the cylindrical cases of most species, grannom cases are four-sided structures that taper chimney-like from front to rear. They build their cases with tiny bits of aquatic detritus, which are glued into shape with an adhesive secreted in their mouths. While several other species build portable cases that they carry with them when they move around searching or food, the grannom larvae are less adventurous. They secure their cases to rocks or the substrate with a silken anchor line. Gary Borger, in Naturals describes this unusual activity. “I’ve observed the Grannom letting itself out on a silk thread and hanging in midwaters; [which] may well be part of drift behavior.”

By safely securing their case with their silken rope, the larvae are able to move in and out of the opening when searching for food without being swept away with the current. Grannom larvae have tannish-green, segmented bodies with dark ginger heads and legs. Typically, clusters of closely located individual grannom cases cover the same rock.

The pupa is the stage most vulnerable to trout.
Photo by Ted Fauceglia

Caddisfly metamorphosis usually takes about 12 months, from egg to adult. After approximately eight months, the larva gradually begins the transformation into the pupal stage. The larva starts the process by cementing the case to the bottom, normally on the side of a rock. It then proceeds to close the opening, completely sealing itself within the sealed cavity. Slowly, the adult body parts (the wings, antennae, mouth, etc.) develop and take shape. The pupa’s legs mutate into miniature oars which assist the pupa when swimming. The pupa’s swimming movement closely resembles that of a water boatman.

Maturation complete, the papa pries the case open and swims to the surface, where emergence takes place. I’ve only had one opportunity to witness a pupa emerge; luckily, it happened streamside, while I was out photographing. The entire process took about ten minutes to complete, and it looked like an exhausting struggle, to say the least. The insect squirmed continuously, almost painfully, until it was completely free from the shuck. After freeing itself, the adult waited a few seconds and then quickly flew off. Based on this experience, it’s reasonable to assume that it takes an equal amount of time for emergence to occur in the stream, which exposes the helpless pupa to the trout for an extended period of time.

In ten minutes, an emerging pupa can float a long distance which makes it easy pickin’s for the trout. Conversely, the adult takes off immediately after hatching and is much more difficult to catch.. Grannom emerge in huge numbers, with literally thousands of insects hatch simultaneously. With that many insects readily available (both rising to the surface and floating within the surface film), why wouldn’t the trout take the pupa as opposed to chasing after the rapidly fleeing adults?

An on-stream example of the trout’s preference for the pupa came during a trip I took several years back to central Pennsylvania to fish the Hendrikson hatch with my friend, Dave Rothrock. Dave advised me prior to the trip that in addition to the Hendricksons, the grannoms might be on, and that I should tie a supply of grannom patterns—“and not just drys,” he admonished. Fortunately, I took his advice, tying a dozen of both adult and pupa patterns.

I met Dave at the stream at about 9:30 a.m., where we donned our gear and headed for the water. Nothing was rising at the time, so we both fished nymphs, until we spotted several fish break the surface. The water boiled with each rise. Within minutes, several caddisfly adults could be seen bouncing across the water.

“The grannoms are on. I just saw several take off,” I yelled out to Dave.

“Yeah, I see them, and so are the Hendricksons,” he answered.

The Hendrickson duns were hatching in the riffle at the head of the pool and were quietly floating downstream, untouched. Dave motioned that he was heading upstream. Since there was a pool of rising fish in front of me, and I had the pool to myself, I decided to stay where I was.

To determine what the fish were taking, I tied two flies on. To the end of my leader, I tied a size 14 Hendrickson parachute dun, to which I attached about 24 inches of 6X tippet with a size 16 Rothrock Pupa at the point. I coated the leader and parachute with floatant. The tippet and pupa were left untreated. The idea was to float the dry but allow the tippet and pupa to ride in or just below the surface.

About a couple of hours later, both hatches ended and the fish quit rising, Dave whistled and motioned that he was headed for the car. I followed. Back at the car, we grabbed a soft drink out of the cooler and each took a big swig.

“You caught a bunch of fish down there, didn’t you?” Dave asked.

“Sure did,” I replied.

“All on the pupa, right?”

“Every one,” I answered. “They wouldn’t even look at a hendriCkson, but you know, it sure looked pretty on the water, and it really worked well as a strike indicator.”

Nonplussed, Dave just stared at me without saying a word.

An American grannom pupa pattern can produce even during a Hendrickson hatch.
Photo by Ted Fauceglia

          Grannom Pupa
          Hook: Curved scud hook (here a Daichi #1130), sizes 16-18.
          Thread: Black, 8/0 or 70 denier.
          Abdomen: Dark brown, olive, and black Hare-Tron dubbing, mixed.
          Wings: Black hen feathers, coated with vinyl cement.
          Legs: Partridge hackle tips.
          Collar: Dark brown fur dubbing.
          Head: Black thread.

Fishing to trout feeding on grannom pupae is not difficult; however, there are two important things to consider.

First, the size and color of the pattern are critical. With any aquatic insect, their colors and sizes vary with the locality and the stream. When I fish a stream that I’m not familiar with, my first stop is at the local fly shop. I talk to the owner to get an idea of what hatches are on and what patterns he or she recommends. I buy one of each pattern and the materials to tie them. I tie duplicates of the pattern that had worked best, either at the stream or late that evening. I prefer to fish my own patterns, but believe me, this small concession has saved me a lot of time and effort. I catch a lot more fish, and I change flies a lot less.

Second, I present the pupa using one of two methods. If the trout are taking the insect while it is floating in the surface film, I’ll treat the imitation with solvent and fish it on a dead drift in the current. However, if they’re taking the insect as it ascends to the surface, I’ll let the fly sink below the surface film and drift drag free with the current. But once the fly reaches the end of its drift, I allow the fly to swing below me until the line and leader straighten out, to simulate the rising pupa. I use a strike indicator or a dry fly as a strike indicator with this technique.

5 thoughts on “The American Grannom (Genus Brachycentrus ) Is a Springtime Gem”

  1. This is excellent stuff but is their any chance of similar articles for your UK fans and customers? The more general videos/articles are transferable across the water but this is very specific. Thanks for all of the videos.

  2. A nice article. I have long wished that Fauceglia would publish another book about caddisses and stoneflies that would be like his book, “Mayflies.” His photography is amazing, and his understanding of bug life and how to use this understanding in a practical fly-fishing manner is excellent. He could call his book “Downwings.”

    1. Liked the article, we primarily fish the Musconetcong River in NW NJ, we see grannoms in two varieties black in the late spring and cinnamon in the fall, the spring hatch is much more prolific. I first observed trout literally rising and eating Caddis pupa off a rock along the edge of the stream, I have observed stream side rocks literally cover with caddis pupa, and I have found you are much more productive fishing a pupa type fly under the surface than anything above water. We get far more Caddis hatches than may fly, and have learned to appreciate grannoms over there more majestic mayfly. Try a thin black bodied (worm like) size 16 Daiichi 1770 with a wing case and fine split tail

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