Pupae, Cases & Tent Wings

(photo by Jessica McGlothlin)

From early spring to well past October, caddisflies offer a three-season smorgasbord for trout.

[by Jason Randall]

FEW THINGS STIR AN ANGLER’S PASSION MORE than the sight of mayflies lifting from the water or a cloud of spinners hovering over a river. Sensational hatches and ostentatious aerial displays of mayflies have long been linked with fly fishing. But the less obtrusive caddisfly offers a more consistent, three-season food source for trout on many rivers and streams.

Depending on regional climate, caddisflies appear well before Mother’s Day and linger long past October. With more than 12,000 species categorized, and still others being discovered faster than entomologists can categorize them, caddisflies are found in nearly every stream, river, and stillwater habitat.

Caddisflies are a widespread and diverse order, Trichoptera, within the taxonomy of insects. Closely related to moths and butterflies, caddisflies have two pairs of wings covered with short hairs. In fact, the strict translation of the Latin word, Trichoptera, literally means ‘hair wing.’ The wings fold over the back of the bug’s body like the pop tent I remember from my Boy Scout days, making identification easy. Another key in identification is the way they fly; flittering and fluttering similar to a moth.

(photo by Barry and Cathy Beck)

Like most aquatic insects, caddisflies spend the majority of their lives underwater; mating and reproduction largely consume the brief aerial phase at their life’s conclusion. Most caddisfly species have a yearlong life cycle from the moment a female releases a fertilized egg until the new generation mates and lays eggs of their own.

To reduce predatory losses to fish and birds, many caddis species emerge with an “all at once” blitzkrieg semblance—hatching en masse overwhelms the predator’s ability to eat them all. In the same vein, since specific caddisfly species often hatch at the same time each year, they’ve earned nicknames like October Caddis or Mother’s Day Caddis as well as a place in the annals of epic angling hatches.

Caddis Larva

A fertilized caddis egg hatches in as little as three weeks after it’s deposited and begins one of the busiest stages of its life. Caddis larvae progress through several development stages called ‘instars,’ living as residents of the streambed where they feed on organic detritus, vegetative material or even other insects. With each subsequent instar, the larva increases in size, outgrows and sheds its exoskeleton and makes another, and gradually matures towards pupation. The larval stage is the longest period of a caddisfly’s life. Because the bugs use silk to construct cases, nets and pupal enclosures, Dr. Edwin Masteller, Penn State Behrend professor emeritus of biology, refers to caddisfly larvae as “the construction engineers of the aquatic world.” I’ve also heard them referred to as “underwater architects.”

Caddisflies generally fit into one of three categories based on their habits during the larval stage. The first group includes the net spinners, including the family Hydropsychidae; bugs that usually favor flowing water and build silk webs to trap food particles.

(photo by Barry and Cathy Beck)

The second group, the case makers, mostly belonging to the Brachycentridae family (Mother’s Day caddis), build and live inside external structures built from tiny pebbles, sticks, and bits of leaves that enlarge as the larva grows. Once inside their makeshift house, case-making caddis rarely leave it. You can see their tubular cases attached to the underside of rocks in the streambed. Though they appear less frequently in the drift than other caddis species and are less available to trout as food, trout do eat them when they can find them, so patterns like the Strawman fly, created by Paul Young, are good to have on hand.

The last group, the free-living caddisflies (Rhyacophilidae), roam and forage among the cracks and crevices of a streambed throughout the larval stage, but make a structure prior to pupation where they remain through the transformation.

The difference in larval lifestyles is important to anglers because it offers several fishing options depending on the species; it’s also one reason there’s such a wide variety of flies that imitate this stage of the life cycle. The free-living caddis are common and widespread, and familiar to most anglers and fly tyers, and patterns can be as simple as one of the many variations of the Green Rockworm.

Caddisfly larva are available to trout nearly year round, but are more common from late winter through late fall. Use smaller flies when fishing well in advance of the anticipated time of emergence because the trout are accustomed to seeing a less mature, and thus smaller, instar. The closer the larva gets to pupation, which begins about four weeks before caddis emerge as adults, use larger flies since the larvae have grown and are approaching pupation and subsequent emergence. Fly tyer Joe Merriell uses hooks as large as size 8 for his Green Rockworm fly, which is a good size when emergence is near.

Dead drift larvae patterns close to the stream bottom since that’s where the naturals live. A bead-head fly or one constructed with the weight in the forward third of the body is a good choice because it makes the fly drift with its head slightly pointing down—the same way the natural drifts. Avoid overweighting the fly. Try to make it look like a nearly weightless insect, not a brick. In fact, I prefer to attach weight to my tippet a few inches above the flies so it gets deep where I need it, but drifts unimpeded.

(photo by Toby Swank)

I often fish a tandem-hook setup of different colored larvae with the second fly tied in as a dropper, using common nymph fishing methods, either with a strike indicator or tight-line technique. However, sometimes I’ll use a combination of a larva and a scud, especially during low light conditions in the early morning and evening when the number of natural larva (and scuds) drifting in the current peaks. Fishing low light conditions also increases the odds of being on the river at the right time; to experience the behavioral drift when large numbers of larvae and other invertebrates intentionally release from the stream bottom and float in the current in an effort to redistribute their population.

The tailouts of riffles and runs are great places to fish. Invertebrates captured in the fast current settle out of the flow in front of eager trout as the flow slows.

Even though free-living larvae don’t make an enclosure until pupation, they still produce silk and often attach a thread to a rock and dangle in the current. You can imitate this by letting your larval fly dangle downstream after the drift. The downstream dangle begins after the line and leader are straightened below you and the fly looks just like a larva on the end of a silken tether.

Subscribe Today

Click here to receive the sport of fly fishing's most authoritative magazine.

Current Subscriber?

Manage your subscription or add a digital edition to your print subscription