During my youth, I knew that some of the flies I was using were supposed to imitate natural aquatic insects and terrestrials. As a seven-year-old, though, I also knew that the yellow Goofus Bug that dad introduced me to caught trout on any river in Northern California, and that was good enough for me. Back then, I was not that interested in bugs or their importance in fly fishing. The study of entomology and its relationship to trout fishing didn’t sink in until I was in high school, and it wasn’t the science classes that sparked my interest, but my greater awareness of the natural world. My knowledge of aquatic insects grew as I fished throughout the West, from the Sierra Nevada to Montana and New Mexico. Along the journey, I learned valuable lessons from my mentors, and by reading as many entomology books as I could find, I increased my knowledge and understanding of hatches and when they occur.
Fly anglers tend to progress through three levels of knowledge about aquatic insects. The first is just an awareness that trout eat aquatic insects and that the flies we use imitate those particular bugs. At the second level, an angler has learned the four main species of aquatic insects that trout eat in a river and can identify a few of them. The third level is when fly fishers realize that they need to learn everything that’s relevant about the species that exists in a river or still water — their preferred habitat, physical characteristics, behavior, when they hatch on each individual body of water, even their Latin names.
Much of that can be learned from books, but knowing when a hatch will happen requires experience. These days, more than in the past, when I depended on the knowledge of my mentors to learn about hatches, experience is easily shared, and keeping up with the latest conditions through social media and on-the-water reports from reliable sources is one way to stay on top of timing a hatch or a spinner fall. I like to share my findings on the water through my blog. For the average fly angler who works all week long and has a family to take care of, the Internet becomes a valuable source of information.
But as with developing and perfecting casting and presentation skills, developing useful knowledge of when aquatic insects hatch requires time on the water over several seasons. Printed hatch charts and Internet reports are one thing; being there — and having been there — is something else again and the only way truly to begin to understand the timing of a hatch. You will understand more about the behavior of bugs by applying your experience on the stream to the knowledge you accumulate by reading informative literature and accessing current reports, because what happens on the water is what really matters.
Printed hatch charts and the angling literature do a decent job of giving you a general sense of the timing of hatches: Baetis mayflies hatch from October through February, midges during the winter, March Brown mayflies during the month of March, Golden Stoneflies emerge after the spring runoff, Hexagenia mayflies from late spring to early summer on particular still waters and rivers, and the October Caddis hatch in the fall. But hatch cycles can vary dramatically with elevation, differences in water temperature and air temperature, and variations in weather conditions from year to year on the same dates. They even vary with the type of water, from riffles to slow-moving sections of a river. Many aquatic insects hatch in or just below the riffles, for example, but some mayflies, such as the Gray Drake and the Mahogany Dun, prefer to hatch from slower-moving water.
In Northern California, the timing of the same hatch will vary greatly from the Central Valley to the Sierra Nevada and north to areas in the shadow of Mount Shasta.
A good example is the Skwala stonefly hatch. On the lower Yuba River, the hatch starts in early January, while on the Truckee River near the top of its watershed, the hatch will occur anywhere from late February to early April. Seasonal variations can also affect timing, as can, increasingly, climate change. There is no such thing as a “normal” year.
Generations of fly fishers have dealt with the problem posed by such variations by employing a simple idea with a fancy name: phenology — the study of correlations between plant and animal behavior. When a specific wild plant blooms, it’s usually an indication that a specific bug also will be hatching. I use a simple formula for when natural appearances of aquatic insects will happen. If there’s been a light, warm winter, wildflowers, songbirds making their nests, and hatches all will be a month early, compared with what the hatch charts say. A heavy, cold winter and a colder than normal spring delay all of these about a month or more.
Anticipating the time of day when the hatch will happen can be trickier, because every day is different, and variations in water temperature, air temperature, cloud cover, wind, precipitation, and a host of other factors that affect when (and if) a hatch comes off and how long it will last are hard to predict. Mother Nature always has the last word. Sometimes, though, the bugs hatch in a daily rhythm, and you can almost set your watch to when the hatch will occur.
As I write this in February, I have been guiding and fishing the lower Yuba River since November, and from high noon to 1:00 p.m., Blue-Winged Olives, Pale Morning Duns, and Pinkie mayflies start to emerge. One way I anticipate more exactly when the mayflies will appear is to watch the streamside foliage. First there is movement in the willows — a flickering in between the branches. Then, suddenly, birds appear, black phoebes and ruby-crowned kinglets, perched on their favorite branches, waiting to intercept hatching mayflies. They know from prior days, weeks, even months of experience when the dinner bell will ring.
Hatches that commence like clockwork, day in and day out, can last for months on some rivers, such as the Little Truckee in late spring and into the summer. For 10 weeks straight, the Green Drakes and Pale Morning Duns were a daily occurrence in the summer of 2018, starting at 11:30 a.m. and ending around 3:00 p.m. I love it when hatches coincide with banker’s hours.
How long the hatch will last is anybody’s guess. Most days, it can last for a few hours, while some days, the switch can be flipped off unexpectedly, and minutes later, the bugs are gone. Nevertheless, if we slow down, cast less, and observe more, we can learn much from the clues provided from the natural world as to when the hatch will likely occur.
If timing the beginning of a mayfly emergence can be tricky, timing the other end of the mayfly’s life cycle, the spinner fall, is a bit easier. Dale Dennis, a longtime old-school guide on the Fall River, taught me much about it. On the Fall River, the spinner fall can be a grand event, with so many spinners on the water’s surface it looks like a moving carpet flowing downstream. Surface-feeding trout gorge on them.
During the warmer months, for the majority of the different species of mayflies, a spinner fall will most often happen when air temperatures are between 58 and 68 degrees. The first clue that a spinner fall is about to begin is again provided by the birds. Sparrows high above the river will be feasting on spinners that are in the process of finding their mate.
The timing of hatches will be different depending on the type of water a particular species populates. Tailwaters are the most dependable. On these rivers, water releases from the dam occur from the bottom of the impoundment, providing an often constant flow of cold water nearly year round, and because the water barely f luctuates in temperature, the timing of hatches rarely fluctuates, either. For example, on the lower Yuba River, where there can be Pale Morning Dun hatches during every month of the year, I carry a thermometer as a way to time the hatch. When water temperatures rise by one to three degrees, it can trigger the emergence of aquatic insects. Knowing this can prepare you so you can efficiently rerig if needed and be ready when the hatch begins.
The timing of hatches on freestone rivers is not as dependable, because the water temperatures vary greatly, as do the flows, and rising or falling water levels can trigger a hatch depending on the species. In the spring, just after the majority of the snowpack has melted, fully mature Golden Stoneflies begin to congregate in the slack water next to the bank below riffles, prestaging for emergence. Caddisflies reliably hatch and oviposit on free-stone rivers in the evenings from May until late October, and evening fishing on a freestone river can provide some of the best action of the day. Bigger and extremely educated fish are more apt to feed during the low-light conditions, too.
On still waters such as Lake Davis, hatches can be very dependable, as long as there are no big changes in the weather and air temperature. During the damselfly migration, the majority of the hatch usually begins at the end of May and ends in the middle of July. During a late spring with low air and water temperatures, however, the emergence will stall, while during an early and warm spring, the nymphs become active earlier. Typically, the nymphs begin swimming to the shoreline around 9:00 a.m., with the peak coming about two hours later. Warming water and air temperatures trigger them to swim out of the protective weed beds and up to the surface to make the long journey ahead shoreward. Once again, the birds — at Davis, California gulls — can tell you when the damselfly hatch has started and where the greatest concentrations of them are. Wind also will affect a hatch and the feeding behavior of trout in still waters. I often find myself sitting streamside or on the shore of a lake, watching how the bugs, trout, birds, and other wildlife interact with each other under current conditions of climate and weather. Understanding the big picture of how an ecosystem works is the key to understanding when aquatic insects hatch and therefore when fish will be interested in what you have to offer them. Books will give you the basics of that understanding, and current information can help you refine it, but to discover what signals a hatch actually is about to begin, there’s no substitute for being there.
Dealing with Masking Hatches
You’ve timed the hatch perfectly, and trout are rising everywhere, but there are three different types of mayflies in the drift, as well as Skwala stoneflies. What bug do you imitate?
This is a complex question, and to make it worse, sometimes trout will key on one just particular bug, with the other bugs “masking” it. The fish actually don’t care about all those other bugs. On the Yuba, for example, when there are multiple mayflies on the water, along with Skwala stoneflies, the fish prefer the Pale Morning Duns. Do they taste better? Are they easier to see? We’ll likely never know.
It took me quite a while to figure out an approach to dealing with masking hatches. What I do is study each trout’s rise form and try to extrapolate from that to what they are eating. To complicate matters, different fish in different parts of the river will be rising to different insects. In February on the Yuba, a trout next to the bank feeding from a foam line will most likely be on the Skwalas. A fish in the middle of the river will see fewer Skwalas and more likely to be eating mayflies. You need to take such differences into consideration.
— Jon Baiocchi
Before and After
Fish are feeding before any bugs hatch on the surface, of course, and they continue feeding after surface activity ends. If you’ve got a good idea when to anticipate a hatch — maybe you’ve lucked into a clockwork hatch that you can count on happening — nymphing below the surface, where trout feed 90 percent of the time, is the obvious pre-hatch tactic to employ for anyone except dry-fly purists. This presentation can be used hours before nymphs transform into adults. Knowing what bugs soon will be hatching will determine your nymph selection. Using a seine and observing a few samplings also will allow you to make a better choice of fly pattern. Small modifications to your rig can make a difference. If you’ve nymphed a run and did not have success, fish it again methodically using more weight or a different pattern.
In addition to nymphs, you can also fish imitations of emergers as they begin their journey toward the surface. Since many emergers hang just below the surface for quite some time, using a dry-and-dropper rig with a soft hackle can be extremely effective. Soft-hackle fly patterns have a lot of movement that will trigger a strike. Try different lengths of tippet from the dry fly down to the wet fly, anywhere from 12 to 24 inches. When fish are bulging just under the surface, use a shorter dropper.
Some mayfly nymphs get stuck in the meniscus film, trapped by the surface tension of the water and can travel great distances in that state, whether or not they emerge as an adult. A floating Pheasant Tail nymph can perform exceptionally well during these conditions. Keeping track of it while drifting is often difficult, though, and you have to sett the hook on any disturbance on the water’s surface,
You can continue fishing after a hatch is over, too, but it requires a different approach. Trout eat leftover duns or spinners, some from the previous day’s hatch, but they do so in some unusual places. I look for back eddies, where the swirling currents create a spinning foam patch. Trapped emerging, adult, and spent aquatic insects are sucked into this vortex, and the surface foam in the eddies provides a layer of security for the trout. One technique I like to use in such situations is to drag a fly very slowly through the foam with slight twitches in the retrieve. This technique works so well that during a week-long trip on the East Walker River, everyone in my crew of fishing buddies caught the same fish from a back eddy close to camp. After the trip, we named the foolhardy trout “Ed.”
Tailouts of major runs also provide another opportunity to continue fishing after a hatch. Duns and spinners often are stranded in slack side water and areas of the river that are not moving. Trout behave in this situation the way they do in still waters, moving from spot to spot looking for food. Sight cast to consistently rising fish.
— Jon Baiocchi
Sources of Information
My favorite books on aquatic insects, hatches, and strategies include anything written by Gary LaFontaine. His inquisitive nature and thorough research were second to none. Gary snorkeled in rivers to study trout behavior and the emergence cycle of the bugs. Another favorite of mine is Mayflies: An Angler’s Study of Trout Water Ephemeroptera, by Malcolm Knopp and Robert Cormier. For a long time, this book was considered the definitive work on that subject. It was written before many of the insects were reclassified in terms of genus and species, but it provides numerous drawings, pictures, graphs, charts, and fly patterns for each species in each stage of life, and I refer to this book almost daily.
On the Internet, there are thousands of entomology-related websites, blogs, and documents. Troutnut.com is geared for the fly angler and has some very useful information and great images. Doing your homework and having a clear picture before you’re on the water will serve you well.
— Jon Baiocchi