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Think Small in the Fall - Aquatic Insect Hatches

Rick Hafele, small aquatic insect hatches in the Fall season Small flies can be frustrating to tie and fish, but if catching fish in the fall is on your agenda then you might just need to think small.

Anglers often overlook small flies – and for good reasons. First, there’s the problem of simply tying on a size 20 or 22 fly to the end of your tippet. If you’re in your twenties you’ll be wondering what I’m talking about, but if you’ve crossed over into that magical world of “middle-age” then you know the new challenge this presents. Second is the belief that small flies catch small fish. Even after years of experience with numerous examples that prove this to be a fallacy, anglers – myself included – tend to hedge their bets and select flies slightly larger than the naturals with the belief that they will be more enticing to the fish. To us, they are easier to see and look juicier, so they must be easier to see and more appealing to trout as well – right? Unfortunately (or fortunately if you’re a trout), trout don’t see the world the way we do. If they did they’d probably starve within a week. To a trout small is often beautiful. Third, many anglers believe small flies can’t effectively hook and hold big fish. However, because of the tiny sharp points and thin wire of small flies, they often penetrate a fish’s mouth quicker and easier than a large fly. Finally, most anglers simply don’t realize the true small size of many naturals. When was the last time you held your fly pattern side-by-side with the natural your were imitating?

From late summer through fall the need to go small is even greater than other times of year. This is largely a function of the life cycles of many important aquatic insects. All those adult hatches you saw in April, May, June and July, laid hundreds of thousands of eggs. For many species those eggs lie quietly through the warm summer months. Then as water temperatures begin to drop the eggs begin to hatch. These young newly hatched insects begin life very small, usually only a half-millimeter in length. Even after growing, sometimes rather rapidly, for several weeks the majority remain small and require small flies to imitate them – typically size 16 or less, and mostly less. The other factor that causes small flies to dominate in the fall is that the major hatches of fall are also small. Hatches like the late season blue-winged olive hatch will be a size 18 or 20. Midges also begin hatching in large numbers again as the weather turns cool and wet in the fall and early winter. These midges will typically be in the 18 to 24 size range. Just right for testing the eyesight of any angler.

The solution to this problem is rather simple: Collect some of the naturals –nymphs or adults – that you’re imitating and place them next to your fly patterns. This will quickly tell you if you are seeing the world through magnified glasses. Then, don’t be afraid to fish a really small fly. Don’t let the media’s message that “bigger is better” influence your pattern selection. Trout don’t watch commercials.

Small Fall Hatches

Okay, you’ve decided to give small flies a try. Here’s a quick overview of the major small flies you will likely run into in the fall and early winter.

Some of the most prolific “small” fly hatches in the fall are the blue-winged olives (Baetis sp.) and tiny blue-winged olives (Acentrella sp., formerly Pseudocloeon). These species occur across all of North America and produce some of the best nymph and dry fly fishing in the fall. Size 18’s will be the largest you are likely to see and if you look at the naturals carefully you will probably need to choose 20’s or 22’s to accurately match the size of these small mayflies. The nymphs are active swimmers, and I find a small nymph pattern fished close to the bottom often works well in the morning before surface activity begins. When duns begin showing up I like to switch to emerger patterns and of course dry flies. Don’t overlook the spinners of these small insects however. Excellent spinner falls can occur from late morning to late afternoon. Rises to these tiny spinners are very easy to miss, so watch the water carefully. If you see the spinners swarming above the water make sure to watch eddies and current seams below riffles for extremely light delicate rises.

Besides these small mayflies, caddisflies also produce good fall hatches many of which are in the small to tiny size range. The most important in many areas is the turtle-case caddis or Glossosoma sp. (see July/August 2003 column for detailed discussion of Glossosoma). Fall hatches of this caddis can be quite heavy in mid to late afternoon. Naturals run from an 18 to 22 in size. Several species of Brachycentrus (American Grannom) also produce good fall hatches. These are perhaps best known for their heavy hatches in April and May, but they rebound with good hatches again in the fall. These caddis run about a size 16, practically giants among the tiny insects of fall.

Fishing tactics for these fall caddis hatches are the same as for other seasons. Pupa patterns can be excellent during the emergence of adults and should be fished from an inch or two below the surface without any weight to near the bottom, which generally requires the addition of some split shot to your leader. An up-and-across cast will allow the fly time to sink. Then let the fly swing up towards the surface like a natural emerging pupa. Adult patterns also work well when fished dry or below the surface to imitate the females that swim to the stream bottom for egg laying.

My final pick for small fall hatches are the midges. Numerous species in a wide range of sizes and colors hatch in good numbers through the fall and winter months. Because of the huge variety of species, and resulting sizes and colors, it is particularly important to collect the naturals for proper fly selection. I almost always focus on imitating the pupal stage, as it seems fish find pupae irresistible when hanging in the surface film or drifting up to the surface from the bottom. Midge hatches can occur almost anytime of the day, but in the fall I find them most common in the late morning through the afternoon. Midge fishing is often best where the currents are smooth and relatively quiet. Trout can be surprisingly selective to these little insects so use light tippets and make good presentations. Pupa patterns should be fished dead drift either in the surface film or a foot or two below the surface. In either case you won’t be seeing the fly, so watch the end of your leader for any hesitation or slight twitch. This is a good example where the fine points and thin wire of the small hooks actually help the fish hook themselves.

Small Exceptions

Of course there are a few exceptions to the “small in the fall” theory. Out west September and October finds the October caddis (Dicosmoecus sp.) hatch in full swing. This caddis runs a true size 8. Interestingly enough even when they are abundant I catch far more fish imitating one of the small hatches than I do these lumbering giants. It’s a puzzle that I still can’t answer. Another exception that works anywhere in the country is large searching patterns like wooly buggers and streamers. This is especially true where brown trout are common. These fish are on their spawning runs in the fall and tend to attack these large flies as much out of a territorial response as something good to eat.

This fall check the size of your fly patterns next to the naturals on the water then put aside your hesitation to go small. You might just find that smaller is bigger after all.

Here are six of my favorite small fall fly patterns:

1- Crystal Flash Blue-winged Olive Nymph:
Hook: Tiemco 2457 or similar style hook (size 18)
Thread: Brown
Tail: 3 to 6 light brown hackle fibers body length
Body: Tan to dark olive crystal flash twisted together and wrapped up hook;shank forming an even slender body.
Thorax: Dark brown or gray dubbing
Legs: Pick out the dubbing from thorax
2- Crystal Flash Blue-winged Olive Emerger:
Hook: Tiemco 2457 or similar style hook (size 18)
Thread: Brown
Tail: 3 to 6 light brown hackle fibers body length
Body: Tan to dark olive crystal flash twisted together and wrapped up hook ;shank forming an even slender body.
Thorax: Dark brown or gray dubbing
Wing: Small clump of gray CDC fibers approximately ½ body length
Legs: Pick out the dubbing from thorax
3- Blue-winged Olive Harrop Dun:
Hook: Mustad 94840 or similar dry fly hook (size 18-22)
Thread: Brown
Tail: 3 to 6 light brown hackle fibers body length
Body: Tan to dark olive dubbing (keep body slender)
Hackle: 4 to 5 turns of good quality light brown hackle
Wing: Body length gray CDC fibers tied in front of hackle and sloping back to rear of fly.
4- Blue-winged Olive Spinner:
Hook: Mustad 94840 or similar dry fly hook (size 18-22)
Thread: Brown
Tail: 3 to 6 light brown hackle fibers body length
Body: Reddish-brown dubbing.
Wings: 5 to 6 turns of good quality light gray hackle. Clip top and bottom.
5- Peacock Caddis Adult:
Hook: Mustad 94840 or similar dry fly hook (size 18-22)
Thread: Brown
Tail: none
Body: 3 strands of peacock herl twisted together and wrapped up hook shank. ;Keep body slender.
Wing: Wood duck flank feather fibers tied in on top and over abdomen slightly longer than hook shank.
Hackle: 4 to 5 turns of good quality light brown hackle.
6- Crystal Flash Midge Pupa:
Hook: Tiemco 2457 or similar style hook (size 18-20)
Thread: Brown
Tail: None;Body: 3 to 4 strands of crystal flash (color to match natural) twisted together and wrapped up hook shank forming an even slender body.
Gills: Small clump of white poly yarn tied perpendicular to shank and trimmed short



Fall often finds Rick Hafele fishing small flies in his favorite Oregon streams. Find out more about fall fishing techniques in Rick’s fly fishing videos,
Fly Fishing Large Western Rivers – Winter, Spring, Summer and Fall

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