By John Juracek

Thirty-three years have passed since Craig Mathews and I published Fishing Yellowstone Hatches. At the time, our little book represented the most complete text available on Yellowstone insect hatches. It remains so today. But much has changed in the intervening years, and were we to publish the book today its list of insect emergences and their relative import would look quite different. Following are some notes on the changes we’ve observed.

The distribution of insect species and their population levels are never static. Fluctuations are natural, sometimes wildly so, for reasons not always well understood. We don’t know for certain what’s causing the changes we see, but one obvious environmental difference between the 1970s (when we started observing area hatches) and today are warmer air temperatures. This is true for both winter and summer. Warmer summer air temperatures raise water temperatures, and we suspect increased temperatures have played a major role in the changes we’ve seen.

The Madison and Henry’s Fork Rivers, two of the finest tailwater fisheries in the world and among the area’s most insect-rich rivers, have each experienced many years of dam-related water flow problems. The effects of these aberrant flows on their respective insect communities are unquantified, but substantial. There are likely many other significant short and long-term factors affecting insect populations throughout the region.

Notes on specific emergences:

Mayflies

Baetis tricaudatus: remains strong in the spring and weaker in the fall on the Henry’s Fork. Fall populations on the Madison below Quake Lake have diminished greatly, yet remain important. Firehole and Madison in the Park populations have declined moderately.

Baetis punctiventris: historically, this was a major emergence on both the Firehole and Madison in the Park, stimulating huge rises of trout. We haven’t seen a viable hatch on either river for many years, and would not include it were our book written today. Substantial population declines on the Henry’s Fork too.

Pale Morning Dun: numbers have declined area-wide over the last couple decades, while remaining an important emergence. The rivers that seem to have experienced the greatest declines are the Madison below Quake, Yellowstone and Henry’s Fork. The last two years (2024, 2025), the Firehole has experienced outstanding hatches, equal to those 40+ years ago.

Green Drake: for simplicity, we had grouped four species of fly under Green Drake–Drunella grandis, D. doddsi, D. coloradensis and Timpanoga hecuba. The most significant change in the group has taken place on the Yellowstone. Here, D. coloradensis (which is actually more closely related to a Flav than the true Green Drake, D. grandis), has gone from a roughly ten day emergence to now lasting six or so weeks. Above the upper falls, it’s by far the most important insect. It should be noted that the spinner falls of coloradensis are the important phase on the Yellowstone, not the actual emergences. Populations of coloradensis and hecuba in the northeast streams of Yellowstone are now subject to serious swings in abundance, depending on the yearly waterflows (and probably other unknown factors).

Brown Drake: this hatch has disappeared from the Gibbon River. Reports of their presence surface now and then, but in checking I’ve only found Gray Drake spinners (which can appear in minor numbers in wet years, and can be mistaken for Brown Drakes by the casual observer).

Flavs: the Henry’s Fork remains the bastion of Flavs, though their numbers have decreased significantly there. We no longer see Flav hatches on the Firehole or Yellowstone. On the Madison below Quake, the hatch had gone missing for many years, but in 2020 there were fishable emergences during July. Looking back from 2025, 2020 now seems like an aberration, not a return to earlier times.

Gray Drake: far less prevalent on Slough Creek and the Yellowstone, but still important. In wet years, Siphlonurus continues as a major hatch on the lower Henry’s Fork.

Callibaetis: in our experience, populations of Callibaetis have always fluctuated in the Yellowstone area. No overarching trend in their numbers or distribution stands out.

Tricorythodes: similar to Callibaetis, populations have always varied from year to year, and continue to do so.

Pink Lady: Epeorus albertae has transitioned from being a minor emergence (barely worth noting) on the Madison below Quake Lake, to being a significant hatch. E. albertae is a warmer water mayfly, and whether its rise in numbers is due to warmer weather or the years-long regime of surface flows from Hebgen Lake is unknown. Emergences and spinner falls both bring trout to the surface, and Epeorus has replaced the Flav as the major evening mayfly on the Madison. Epeorus have been less numerous in the last six years, since the river is once again being fed from the bottom of Hebgen Lake.

Attenella margarita, Serratella tibialis: neither species of mayfly warrants inclusion in a book of hatches today, though both are still in evidence on the Yellowstone.

Heptagenia: for the last 5-7 years there have been notable autumn populations of Heptagenia emerging from Soda Butte Creek and the Lamar River. No mention would be given today to Heptagenia on the Yellowstone.

Caddisflies

Nectopsyche: readers familiar with Fishing Yellowstone Hatches will note that this caddis doesn’t appear in our book. That’s because back in the day, Nectopsyche (White Miller, colloquially) were nothing more than a token presence on the Firehole and Madison River (in the Park). As the Firehole has warmed over the years, populations of Nectopsyche have exploded, essentially becoming a “new” hatch for fishermen. Nectopsyche are far and away the dominant caddis on the Firehole, with good numbers appearing yearly. Emergence takes place from early June through September. Numbers on the Madison fluctuate widely year to year. Both emergence and egglaying phases are important. I’ve had two professional entomologists attempt to identify this fly to species level for me. Neither was confident enough in their assessment to offer a judgment.

Brachycentrus: Mother’s Day caddis have long been notorious for year to year population fluctuations. They remain that way, but the trend is definitely to the downside.

Hydropsyche: the Hydropsyche complex (we covered four species in Hatches) have historically been the most important caddisfly genus for anglers in this area. They appear to be suffering the most serious population declines of the caddis we cover. These declines are not river specific, but rather area-wide. Still important to anglers and trout.

Helicopsyche: no particular trends noticed.

Glossosoma: populations on the Madison seem to be fluctuating more now than in years past.

Oecetis: I don’t have enough recent experience to comment on the state of this hatch.

Cheumatopsyche: like their Hydropsyche relatives, numbers are down on the upper Henry’s Fork. The Gallatin River in Yellowstone Park and Montana also has a fine July Cheumatopsyche emergence (we didn’t list it in Hatches), and until 2020 had been trending stronger. 2020 through 2025 saw weaker emergences, more akin to historic norms.

Lepidostoma: numbers much reduced on the Yellowstone.

Arctopsyche: remains abundant on the Madison.

Hesperophylax: this beautiful caddis is now scarce enough that we would no longer include it in a book of hatches.

Rhyacophila: area-wide, numbers have declined dramatically.

Micrasema: no longer prevalent enough to constitute a “hatch”.

Mystacides: there have been significant habitat changes on the Henry’s Fork where this caddisfly was historically important, but they are still present in reduced numbers.

Stoneflies

Salmonfly: well known for dramatic population fluctuations. No obvious trends.

Golden Stone: no obvious trends.

Little Yellow Stoneflies: appear to have declined on the Madison, but not dramatically.

Damselflies: numbers on Henry’s Lake are much reduced from historic levels. Elsewhere, we’ve noticed no trends.

Midges: spring numbers on Hebgen Lake remain strong, summer numbers are down. Midges remain significant year-round on rivers like the Madison and Henry’s Fork.

John Juracek is a fly fisherman, writer and photographer from West Yellowstone, Montana. For twenty-some years he was a partner at Blue Ribbon Flies, a local fly shop, and is currently the head casting instructor at the School of Trout and Anglers Academy. His writing credits include Yellowstone: Photographs of an Angling Landscape, Fly Patterns of Yellowstone, Fishing Yellowstone Hatches and Fly Patterns of Yellowstone, Volume Two.

He is considered one of the sport’s expert fly casters and instructors and offers casting lessons for $100/hour at [email protected] or (406) 640-2828.