How many times have you been out on the river during a hatch only to watch trout going bonkers over every other bug on the water but yours? Frustrating right? Well regardless of how good you might think you are at matching the hatch sometimes this is just the way it goes. Below is a high level look at basic entomology as well as some general process for fly selection that may be helpful during your next such encounter.
Insect Life Cycles
The study of insect life (entomology) can get complicated real fast. Luckily, you don’t need to know all the underlying details of the insect world to be able to match the hatch. A solid understanding of the few life cycle variations is really all that’s needed.
There are four main categories of insects that trout eat on a consistent basis (midges, mayflies, caddis, and stoneflies) and each one of these insect groups experience different stages. The first group we will discuss undergo the greatest transformation and experience what is called a “complete metamorphosis”. These insects go through the egg, larva, pupa and adult stages. The second group undergo a partial or “incomplete metamorphosis”. These bugs experience only the egg, nymph, and adult stages. Here is the breakdown as it relates to our four main insect categories:
Complete Metamorphosis = Midges and Caddis
Larva – The larva stage comes directly after the egg stage. Larva are worm like critters that are segmented throughout their bodies. They come in multiple colors like red, black, cream and pale green.
Pupa – The pupa is the intermediate stage of an insect. It contains a large thorax which holds the wings and legs of the emerging adult.
Adult – The adult stage comes right after the pupa has fully developed and emerged from beneath the water’s surface. The adult will sit on the water for a time until its wings are dry enough to fly away. It will then mate, come back to the water to lay its eggs and die.
Incomplete Metamorphosis = Mayflies and Stoneflies
Nymph – The nymph stage comes directly after the egg stage. Unlike larva that start out as worm like creatures, nymphs are born as small versions of the adult insect. They have a thin exoskeleton containing gills, legs and multiple tails. Nymphs can be classified as either clingers, burrowers, swimmers, or crawlers.
Adult – The adult stage comes right after the nymph has fully developed and emerged from beneath the water (mayflies emerge through the water’s surface as they exit their skin, stoneflies most often crawl out of the water via rocks or tree branches where they shed their exoskeleton). The adult will then fly away, mate, and come back to the water to lay its eggs and die.
Note: Even though an emerger isn’t an actual “stage” of a bug’s life cycle, it is a state we try and imitate on the river. Since this transitional time between pupa/nymph and adult is when an insect is most vulnerable to trout, it is important we learn how and when to fish this pattern.
Selection Process
A general rule of thumb when matching the hatch is to think progressively. Seasoned anglers say it’s a three step process. First you identify the profile of the insect you want to imitate, then the size, and lastly the color.
So what is the best way to identify the profile of a bug? Well it starts by looking around you. Are there bugs flying in the air or sitting on the water? If you don’t see anything there then lift a rock or two, or better yet, strain the river to see what is floating through the water column. Once you get some samples take a look. Start by identifying the category of bugs you see. Are you finding midges, mayflies, caddis, or stoneflies?
After you identify the category, you then want to think about the life cycle stage these little critters are in. Are they in the larva/nymph, pupa or adult stage? Identifying these major categories and stages is what we call matching the “profile” of the bug. This is step one in selecting the right fly pattern from your box.
Once you’ve identified the profile of your bugs you should be able to eliminate about 3/4 of the flies in your box. For instance, if you find the majority of the bugs in the water are midge larva (Category=Midge, Stage=Larva) then you know what section of your fly box to pull from, the midge larva section.
Next and just as important is to identify the size you want to go with. Before you reach into your box and pull out a size 18 midge larva, take a closer look at those little worm like things squirming around in your seining net and ask yourself if you should go a size bigger or smaller? Dialing into the size of your fly can help you go from a 2 fish day to a 40 fish day.
Lastly you will want to think about the color of your fly. If you see one red midge larva in your seining net and 5 or 6 cream colored larva, then go with the cream color. If you can’t identify any specific color (they all look dark) then go with something dark, maybe a black or dark olive. Remember, this sounds easy now, but matching the hatch in the field is often anything but easy. Do the best you can. The more you practice, the better you will get.
Below is a chart that will help you better understand the selection process as well as the basic insect hatches and their life cycles.
Prepping Your Fly Box
Now that we have gone through what the selection process on the water should look like I want to give you a bit of a cheat sheet for how bugs and their life cycles should align with your fly box. Though there are literally hundreds of flies out there to choose from, in general I like to find a few solid patterns that consistently produce and stay with those. This will keep your box less cluttered and easier to navigate when you are actually on the water. The below is a selection of patterns that work well for me.
Midge
Larva – Pure Midge Larva
Pupa – Zebra, Mercury Midge, Brassie, JuJubee Midge, Tailwater Tiny, Rainbow Warrior
Emerger – RS2, WD40, Mayhem
Adult – Adams, Griffiths Gnat
Mayfly
Blue Winged Olive
Nymph – Pheasant Tail, JuJu Baetis
Emerger – RS2, WD40, BWO Barr Emerger, Mayhem
Adult – Adams, BWO, Spinner
Pale Morning Dun
Nymph – Pheasant Tail, Split Case PMD, Crack Back PMD
Emerger – PMD Barr Emerger
Adult – PMD
Green Drake
Nymph – Hare’s Ear (olive)
Emerger – RS2 (olive), CDC Green Drake Emerger
Adult – Western Green Drake
Red Quill/Hendrickson
Nymph – Pheasant Tail, Hare’s Ear
Adult – Red Quill (male), Hendrickson (female)
Trico
Nymph – RS2, Sunken Spinner
Adult – Trico Spinner, Griffiths Gnat
Caddis
Larva – Brassie
Pupa – Hare’s Ear
Emerger – Barr’s Graphic Caddis, Royal Gorgeous
Adult – Elk Hair Caddis
Stonefly
Nymph – Pat’s Rubber Legs, Twenty Incher, Golden Stone
Adult – Stimulater, Yellow Sally
Attractors/Terrestrials, Worms and Scuds
Wet Attractors – Copper John, Prince Nymph, Hare’s Ear, Rainbow Warrior, Tailwater Tiny
Dry Attractors/Terrestrials – Royal Wulff, Chubby Chernobyl, Humpy, Renegade, Madam X
Worms and Scuds – San Juan Worm, Rock Worm, Scud
Additional Resources
Colorado Guide Flys (Pat Dorsey)
Flyfisher’s Guide to Colorado (Marty Bartholomew)
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