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Entomology

There are tons of different bugs and food sources that trout eat throughout the year and it can be quite daunting. Honestly, you don’t need to know every single type of bug hatching but knowing a few can make your days out on the water much easier. We’ll get into the basic bugs and how to identify them.

Midges:

Midges are typically the smallest hatch that we see on all trout waters. And when we say small, we mean it. The majority of the time these bugs are hatching in sizes 24 and 26, but they’ll hatch as small as a 40. On the other hand they’ll hatch as big as a size 18, but this happens on very rare occasions. Midges are rather easy to identify and also have the simplest life cycle. Midges can be seen as red, tan, or olive when in the larva form, and typically black or brown when pupa and adults. Midges begin their life as an egg and will hatch forming into a larva. During this stage they’ll reside in the river bottom for up to a year. From here they’ll begin their pupating stage, which is essentially the in-between stage from larva and adult. As the pupa get pushed towards the surface of the river, they will begin breaking out of their case. This is what we call an emerger, although this is technically not a life cycle stage because these are still pupa. Once the midge breaks from its pupa shell, an adult is sitting on the surface of the water. Adult midges don’t live for very long, typically less than a day. They come from their pupa shell without a mouth or digestive organs, their sole purpose is to create its next generation and die, literally. While the males wither away the successfully mated females will fly onto the water and lay their eggs where they will parish afterwards.

Mayflies:

There’s a ton of different mayfly species and grouping that can make it daunting at times to figure out what kind of mayfly it is. Don’t let this deter you though, when fishing mayflies if you have the general size and color the fish won’t mind. Depending on the species, they will have two or three tails that are short or long. They can have a long, slender body or a short and stout one. Again, there’s a ton of variety. All mayflies have the same life cycle though: nymphs, adult dun, and adult spinner. Mayflies begin with eggs that get lodged in the river bottom, turning into nymphs that will live in the water for a year. There isn’t a second water-bound stage for mayflies, they simply swim to the river’s surface and begin to break through their shell. Once fully broken through its shell, an adult dun sits on the surface until its wings dry out. Duns are the reproducing adult and the most active, and like midges they have no mouth or digestive organs. Once the duns successfully reproduce there will be the spinner adult stage. Spinners will lay eggs with their remaining energy and eventually lay flat on the water where they will die. The adult stage of mayflies typically lasts only one day.

Caddis:

Caddis flies are another diverse grouping of aquatic flies that come in many varieties of sizes, colors, and shapes. It isn’t always easy to identify a caddis, but if you see moth-like flies hanging near the water then it’s likely a caddis. Fun fact, caddis flies are actually a sister-family of butterflies and moths, hence their similarity in looks and life cycle. Much like butterflies and moths, caddis have a complete life cycle that involves a larva, pupa, and adult. There are two different types of caddis larva, free living and cased. Free living larvae move around the river bottom, while cased caddis tend to latch onto rocks or branches to blend in. Pupa are the intermediary stage between larva and adults where they metamorphosize rapidly. They will swim towards the river’s surface and begin to emerge into an adult. Adults, like all other aquatic insects, have no mouth or digestive organs and their only goal is to successfully reproduce. Egg-laying adults are unique as they don’t lay down on the water, instead you’ll see them “jumping” to and from the surface. This is an adaptation to avoid predation when laying eggs. Most caddis adults will be out of the water one to three days. 

Stoneflies:

Stoneflies are on average the biggest aquatic insect that lives in trout waters. There are famous hatches like the salmonfly, golden stone, skwala, and yellow sally. Their distribution isn’t as expansive as it used to be due to changing water conditions. Stoneflies require the purest and coldest water out of any aquatic insect. The nymphs can be identified with their extended, tapered body, noticeable antennae, six legs, and two wing cases. The adults look almost identical to the nymph stage, but with two pairs of long wings that make them look awkward when flying. They too come in a large variety of sizes and colors, so don’t expect to be looking at the same bug each time. Stonefly cycles are simple, having an adult and nymph stage. Nymphs will reside in the river bottom for 1 to 4 years, depending on the species, and will migrate to the river’s edge where they crawl onto rocks, logs, and plants and break through their shells as an adult. The adults can live anywhere from a day and up to a week, just depending on the species. Once the adults successfully reproduce, the females will drop their eggs on the surface of the water. Most adult stoneflies die on the edge of the river, rather than the surface like midges and mayflies. 

Scuds, Leeches, Worms, Eggs:

Scuds aren’t present in all waterways, but in the waters they’re present they’re a valuable food source for fish as they are highly nutritious. Scuds are easy to identify, they closely resemble a rolly-polly or pill bug and usually tan, gray, or olive in color although the dead ones are usually an orange or pink color. They often reside in large mattes of weeds or sandy patches of river bottom. Their entire life cycle is spent in the water, so expect to see them in a variety of sizes.

Leeches, like scuds, aren’t present in all waters but are a very important food source for trout. Leeches are very easy to identify, resembling a slug that is olive, brown, or black in color. They also live in weed mattes and sandy patches of river bottom, but can also be found underneath larger rocks and boulders. There is a common misconception that all leeches suck blood, which is far from true. The vast majority of leeches feed on vegetation, so don’t let the water scare you from fishing. Their entire life cycle is spent in the water, so expect to see them in a variety of sizes. 

Worms, both aquatic and terrestrial, are found in all waterways. Aquatic worms are typically very small and often referred to as annelids. Annelids are usually red in color, but can also be tan, wine, or olive. Annelids’ entire life cycle is spent in the water, so expect to see them in a variety of sizes. Terrestrial worms are those that reside on land and are often flushed into the water during heavy rains, snowmelt, or heavy flows that take up the bank. Terrestrial worms are often much larger than aquatic worms and trout tend to engorge themselves on them when available. When thinking of terrestrial worms, think no further than a standard nightcrawler, they’re usually tan or brown. 

Eggs aren’t always present in the water, but when or where fish spawn they’ll be in the water. We usually fish eggs anywhere from October through May because our waters have spawning brown and rainbow trout. Brown trout eggs don’t hatch until the spring, so even if you don’t have rainbow trout in your waters, their eggs will still be present. Rainbow trout spawn in the spring and their eggs develop very fast in order to hatch in the spring as well. Eggs can come in a variety of sizes and colors, so have your box filled with a variety of patterns.

Terrestrials:

Terrestrials have nothing to do with aquatics or river hatches, but still make a large portion of a trout’s diet during the summer months. Terrestrials are a group of flies that anglers frequently fish, such as grasshoppers, crickets, beetles, moths, ants, bees, wasps, and blowflies. All of these flies have a life cycle that is 100% based on land, but often reside near the river banks. Trout will often prey on them when they stumble onto the water’s surface. 

Although we know this doesn’t cover every single hatch and all of their nuances, this is enough to get you started. We do, however, carry a book with a ton of information and insight of our hatches: (Link to western hatches book) This book will cover everything you need to know for western hatches and being prepared when out on the water. 

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