Beginners Guide to Aquatic Bug Life & How to Match the Hatch

I think one of the most intriguing aspects of trout fly fishing is the incredible range of forages (read: food sources) that they will feed on. From seemingly microscopic midges to 3-inch-long cicadas, there aren’t many bug species that trout won’t take a swipe at, given the chance. “Matching the Hatch” has long been the mantra of fly anglers everywhere, and for good reason, trout can be persnickety creatures when they’re keyed in on a very specific insect. This article is meant to serve as a cursory guide to the most common aquatic and terrestrial insects that you might encounter during your time on the water. 

Table of Contents:

How to Find and Identify Bugs on the Water

Aquatic Insects Trout Can’t Resist 

How to Find & Identify Bugs on the Water

Step 1: Find the bugs

Unless you’re seeing flies come off the water while hatching or mating, figuring out what bugs are in or on the water can seem like a daunting task. 

If the flies are in the air, simply catch one and hold it near your fly box and do your best to match the color and size of the bug. 

If there are no bugs on the water, they’re likely all below the water’s surface either embedded under rocks or in some woody structure or in the water column. The best way to capture and identify these bugs is via a seine kick-net or by simply flipping over rocks and seeing what nymphs are attached to or crawling on them. 

Step 2: Identifying the Bugs

This step can be the trickiest one if you’re interested in perfectly identifying which species of aquatic bug is in your hand or seine. There are many field guides available from State fisheries agencies that will be regionally specific to your area, like this great field guide from West Virginia’s DEP that shows many common aquatic insects with handy imagery that you can download and save on your smartphone. If you’re more interested in simply matching the bugs to the flies in your fly boxes, the process is as simple as comparing the live animals to your flies.

Pro Tip: If you find bugs in abundance that don’t match any flies in your box, snap a few pictures so you can match them while sitting at your tying desk, or in your local fly shop!

Common Insects You’ll Find While Fly Fishing

There is an infinite number of bugs that you might encounter during your time wading or floating on trout rivers, creeks, and streams, but this quick guide will help you identify those bugs and effectively match what food source the trout are keyed in on!

It’s important to note that this guide is an overview of the most common aquatic insects familiar to fly anglers, for more in-depth and regionally-specific guides, field guides for your area can typically be found with a quick and simple Google search.

Caddis

When you hear someone refer to a fly as a caddis, they’re referring to bugs that are members of the order Trichoptera. Caddis spend their early life stages in the water, and once hatched fly into the air taking on a more terrestrial lifecycle before returning to the water to mate. 

Caddis Nymphs

For the most part, the caddis nymphs you’ll come across will either be referred to as “cased” or “uncased”. These terms refer to the cases that caddis nymphs build around themselves for protection and for camouflage. Flies to match caddis nymphs!

Caddisflies

Caddisflies hatch throughout the spring, summer and fall depending on the species. They are easily identified by their long antennae and tent-shaped wings. Flies to match the caddis hatch!

Mayflies

When most people think about dry fly fishing a hatch, most think of the iconic mayfly, with its curved body, teardrop wings, and penchant for blanket hatches. They’ve become synonymous with fly fishing since the pastime was developed hundreds of years ago. There are approximately 3,000 unique species of mayfly in the world, and 300 of those are native to the United States. Flies to match the mayfly hatch!

Stoneflies

Stoneflies are a perennial favorite for both trout and the anglers pursuing them. Fish love them because they’re big sources of protein that are commonly available in abundance, and anglers love them because of the aggression they bring out in trout. The name stonefly refers to the order Plecoptera. Easily one of the largest aquatic nymphs and flies anglers will encounter. If you ever hear someone talking about the legendary skwalla and salmonfly hatches, they’re referring to a duo of insane hatches that pop off in the American west every summer, and both of them belong on any dry fly angler’s bucketlist! Flies to match stonefly adults and stonefly nymphs!

Midges

If you’ve ever been out on the water and seen a cloud of mosquito-like insects that don’t seem interested in biting you, the odds are that you saw a swarm of midges. Midges are closely related to mosquitoes and look like them, but they don’t bite. More importantly, they make up a huge percentage of a trout’s diet. This is for a few reasons. Midges are pretty universal, being found in large numbers in many bodies of water. But, one of the biggest reasons they’re so important for fly fishing is that they’re one of the few insects that can hatch year-round. This means that midges are one of the most effective flies to use. Many anglers are skeptical of tiny midge patterns since it’s hard to believe that trout can even see something so small. Yet, midges continue to be one of the deadliest flies in a box. You can learn all about these incredible insects and how to fish midge flies effectively in our in-depth guide, here! Flies to match the midge hatch!

Midge Fly Fishing – Tips to Catch Trout All Day

Isopods – Scuds, Sowbugs, Freshwater Shrimp, etc…

When we talk about isopods like scuds, sowbugs, or freshwater shrimp, we’re referring to a class of insects that spend the entirety of their lives in the water, unlike the fly species previously mentioned in this article. These little bugs are generally herbivorous, preferring to feed on aquatic vegetation found in slow-moving spring creeks and coldwater streams. Anytime you’re fishing around plants and exposed roots, there’s a very solid chance you’ll find scuds and sowbugs hanging around. Flies to match the sowbugs and scuds!

Terrestrial Insects – Grasshoppers, Spiders, Ants, Beetles, etc…

The term terrestrial refers to insects that spend their entire lives out of the water until they accidentally find themselves on the surface of the water. Popular examples of these would be grasshoppers, cicadas, ants, and beetles. Most of the time, you’ll find these bugs splashing down during windy and stormy days. When trout encounter these struggling bugs on the surface, their response is typically violent and exciting! Flies to match the terrestrials!