I remember my first time seeing a caenis hatch. I was only a boy, but man did I get excited. But that was short lived.
When you land on a hatch and see fish feeding, it is usually a good thing. This time the water was boiling. But no matter what I tied on, the fish just were not interested.
What is it
There are actually two different families that cause this reaction in fish, and for a long time they were thought to be the same.
That confusion has a specific origin.
When Vincent Marinaro published a 1969 article in Outdoor Life about the caenis hatch on Falling Springs in Pennsylvania, he had misidentified the bug.
It was actually Tricorythodes. The mistake was corrected in the early 1970s, but the names got tangled in angler shorthand for years after, and even now you will hear people talk about a caenis hatch on a river when what they saw was a trico.
Both belong to the mayfly order. The main difference is location and behaviour. Caenis is best known in Europe as a stillwater bug, though it turns up in North America too. Trico is the North American cousin, mostly on rivers.
Either way, both can ruin an afternoon of fishing.
Why one fly cannot match it
I have tried and failed to catch fish by tying up caenis at the vise, and I am not the only one.
Tying a size 26 fly is challenging, but oddly it is not the most challenging part. First let's look at what these are, to understand what is happening.
A caenis or trico is a very small mayfly. Caenis sits in the family Caenidae, trico in Leptohyphidae.
Both share the same body plan: three tails, only forewings and no hind wings. Hook sizes run from 22 down to 26, with some caenis species going smaller still.
The nymphs of both carry covered gills that let them survive on silty bottoms, which is why caenis concentrates in reservoirs and slow river reaches while trico is a river bug on moving water.
The winged adults look almost identical without a hand lens, which is why the two got confused for years.
The size alone causes a problem. But the fish are not keying on one fly. The bigger problem is the sheer volume.
Say you have your box open and a size 24 spent tied on. You have already dropped to 7X or 8X tippet, because anything heavier is a rope next to a hook that small.
Your leader is probably fifteen feet or you are not getting a drift over these fish anyway.
Every one of those choices costs you presentation, and now you are trying to land your one fly in a drift lane holding thousands of naturals. From the fish's side of the surface, your fly is a single grain in a bowl of rice.
We have all heard how a mayfly lives for a day. This one plays out in an hour or two.
The four stages, all at once
Materials
The reason no single fly matches this hatch is that four life stages of the same insect sit on the water at once.
It starts as an emerger, the nymph pushing out of its case in the surface film with wings still crumpled and coming free.
Once out, it stands briefly as a sub-imago, or dun. That is the first winged stage: the wings are dull and slightly opaque, the body is soft, and the flight is weak.
Within a minute or two it lifts off and makes for streamside vegetation, where it moults a second time. The old skin splits down the thorax and the fully mature imago, or spinner, emerges with clear glassy wings and a longer, harder body.
The spinners then form a mating cloud over the water, drop and rise together, and once the females are mated they return to the surface to lay eggs. Both sexes die spent, wings flat on the film.
On trico there is one more wrinkle worth knowing. The males and females do not hatch at the same time. Males emerge at night, roost in the streamside vegetation, and moult to spinner before dawn.
The females emerge in the morning. When they moult and rejoin the males in the mating cloud, the swarm is already waiting.
That is why anglers walking up on a trico morning often see the spinner cloud before they see any duns on the water at all. The females do the emerging you can watch. Half the hatch has already happened in the dark.
At the peak of the hatch, every one of those stages is on the same square metre of water at the same time.
The only edge that works
Most anglers pack up and go home when they land on a trico hatch, and they are not wrong.
Either I am too stubborn, or the fact that just being out is good enough for me, I stick around. Sometimes I feel like I am just observing, and there is a lot of fulfilment in that on its own.
I do not have a secret weapon for catching on a trico or caenis hatch.
The only thing that has ever worked for me is fishing spinners on the edge, picking a trout that is not in the middle of it. That fish sees fewer naturals in its lane, so a good spent pattern reads slightly cleaner in its window. It is a small edge but it is real.
The edge is anywhere the density of naturals drops off. The obvious one is the outside of a foam line, where a wind seam narrows the drift into a ribbon and the trout holding just outside it sees only what breaks the line.
Another is the back of a feeding pod, where the fish that dropped to the tail has fewer targets to choose from than the ones stacked at the head.
On stillwater, wind lanes do the same job, collecting spent spinners into a corridor a few feet wide with clean water either side. Any trout holding on the edge of that corridor is a fish worth casting to.
The other option is to fish something the pod has not seen for the last hour. A caddis, an ant, a small hopper if the season is right.
When a fish has been feeding on identical spent spinners for ninety minutes, the one thing that stands out is anything that is not one. It does not always work. Nothing about this hatch always works.
Two different flies from the same order, two different parts of the world, and they all but shut down fishing for the evening.
But man is it a sight to see.