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It is not uncommon to be sitting on a rock or log midstream and peer down into the stream and see hundreds of these little chimney cases lined up on gravel, rocks, plants, or submerged wood. The caddis cements its case with silk to its substrate, with the open end of the case pointing upstream. A closer view reveals that the larva’s bristly middle and hind legs are much longer than the forelegs. These long legs are splayed out at night to filter and capture bits of algae, detritus, and even animals from the current. If food resources become limited or a predator becomes threatening, a larva will detach its case and move up or downstream to a new feeding area. Anchoring itself with a silk strand, it can rappel downstream to a new substrate, sometimes just an inch or two, sometimes more. Fish can and do eat cased caddis, and anglers that carry a Peeking Caddis imitation often can do quite well in early spring. Caddis cases provide some protection from many predators, but they are also important in respiration functions, particularly during the pupal stage. Just prior to pupation, the caddis will seal most of the entrance of its case with silk, leaving a small hole for circulation. Inside, the caddis will transform from larva to pupa, taking two to three weeks for the complete metamorphosis. The emerging pupa or pharate adult, completely transformed, will use its mandibles to escape the case. The pharate adult
will swim to the surface, and the adult, freeing itself from its shuck, will emerge. The pharate and emerging adults have a bright green body with dark wings. The adult Grannom is rather nondescript in appearance, with tear-shaped wings and antennae about the same length as the body. An X-Caddis pattern with a green body is a simple yet effective imitation during the hatch as fish key in on the caddis as it struggles to emerge from the surface film. After emergence, the bright green abdomens of B. americanus darken, taking on a brownish-olive color; other species of Brachycentrus have dark brown bodies. In some of the Grannom species, there is a distinct lateral line observed with good eyes or magnification. Watch for American Grannom to begin emerging in the mid-afternoon. Unlike mayflies, adult caddis can live for several weeks, depending on weather conditions. Their mouthparts are used to take up moisture, preventing dehydration during their short adult lifespans. Mating ensues soon after emergence, and it is not unusual to see hundreds of caddis coupled end-to-end on streamside vegetation. Males, size #14, are smaller than the females, size #12. Males disperse after mating, while females return to the water after some time to lay their eggs, either by dipping their abdomens and dispensing their eggs or by diving underwater to oviposit. If trout are feeding on the surface, skitter or drag a caddis pattern across the water. Egg-laying females are best imitated with a bit of green dubbing tied at the tip of the abdomen. When the action slows or ceases, try pinching a small split-shot several inches above the fly and allowing it to sink. Lower and lift your rod to simulate a diving female. A hair-wing or Antron caddis pattern does a good job imitating the diving egg layer. Fish these in the surface film or allow them to sink. Be prepared for opening day this spring with flies to imitate the American Grannom. Park them in your fly box beneath the Blue Wing Olive (Baetis tricaudatus) and Hendrickson (Ephemerella subvaria) mayflies and enjoy your time on the river.
Ann Miller is the author of Hatch Guide for Midwest Streams (Frank Amato Publications, 2011; ISBN -13: 978-1-57188-481-7; $29.95). She is republishing the book in 2021.
Spring 2021
Caddis undergo a complete metamorphosis, so the immature stage is referred to as a larva. Eggs hatch soon after they are laid in late spring, with the new larvae growing rapidly over summer and early fall. Development slows in winter during the fourth or fifth instar stages. They are case builders, constructing a chimney-shaped case with perfectly aligned transverse stacks of plant material, like a tiny log cabin. The larva uses silk to cement the case fragments together, resulting in a very sturdy home indeed.
by Ann R. Miller
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Here in the Midwest, we have few caddis hatches that are more reliable than Brachycentrus americanus, or the American Grannom. A steady producer in streams and rivers with good oxygen and current, this caddis starts hatching in mid-May, soon after or concurrently with the Hendrickson mayfly. The American Grannom goes by many common names, including the Mother’s Day Caddis, Black Caddis, Popcorn Caddis, and possibly even more. There are other species that hatch after B. americanus, including B. numerosus and B. lateralis, so that it can seem like this caddis hatch goes well into the end of May.
MICHIGAN Trout
A Caddis to Count On
