What They Look Like - Grannom Caddis

 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.

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.”

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.

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.

Larvae

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.

Pupae

Maturation complete, the papa pries the case open and swims to the surface, where emergence takes place. The Pupa emerges to the surface and, like many other aquatic insects, emerges from its pupal shuck into an adult. This process can take around 10 minutes which it quite a bit longer than other insects. 

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. Next time your out and see Grannoms, toss on that Pupa imitation under an Elk Hair Caddis!

See you on the water,
Lance