What Do Trout Eat?2018-07-01T14:39:44+00:00

What Do Trout Eat - March Brown Dun - Fly Fishing Atlas

What Do Trout Eat?

 

Trout eat an amazing variety of insects, minnows, worms, crustaceans, amphibians, reptiles, and even rodents!  Fishing for trout would be too easy if they ate these foods whenever they came across them, but they don’t.  So how is it that some anglers land so many trout?  Are they just really lucky?

Having an amazing day of trout fishing isn’t really about luck at all.  Successful trout fishing is about successful observation.  And even though fishermen are known to tell tall-tales, if they’re being honest they would tell you the same.  Accurate imitation of natural trout foods is an incredibly effective strategy to catch significant numbers of handsomely sized mature trout.  Presenting those imitations with a fly rod is by far the most effective method.  For some fly pattern suggestions on where to start, take a look at our picks for best flies for trout.

The appearance of the foods trout eat will vary from one water to the next and even one day to the next.  Their size, color, shape and movement can be very different depending on the location and which phase of their life cycle happens to be occurring.  Before you can imitate a particular trout food you need to develop the ability to recognize it for what it is.  And to help you accomplish that – Fly Fishing Atlas explores the predominant aquatic insects that trout eat.

 

Mayflies

What Do Trout Eat - Hex Mayfly Dun - Fly Fishing Atlas

A Hexagenia or “Hex” Mayfly Dun

Mayflies have been the focus of attention in the sport of fly fishing since the very beginnings of the sport.  The 4 life stages of the mayfly pass through extraordinary changes as they pass from egg, to nymph, to dun, to spinner.

Egg to Nymph

Adult female mayflies deposit eggs onto the surface of the water, and sometimes below the surface.  The eggs sink and stick to the various structures on the stream bed or lake bottom.  Hatching times vary between a few days to a few weeks.  The eggs then hatch into tiny nymphs that crawl or swim to their preferred environments for feeding and growth.  Mayflies spend the majority of their life cycle in these areas feeding on plants and going through metamorphic skin changes as they grow.  Trout eat mayfly nymphs as they become vulnerable by swimming about or becoming dislodged and drifting in the current.

Nymph to Dun
What Do Trout Eat - Immature mayfly nymph - Fly Fishing Atlas

An immature Mayfly Nymph

When the nymph is fully mature it will float or swim to the surface to transform into the adult dun mayfly.  Some mayflies make practice runs to the surface leading up to their emergence.  Nymphs are very vulnerable to trout during this time.  Trout eat mayflies with relative ease as they leave the bottom and move through the water column to the surface.  When emergence occurs, the nymph moves to the surface and splits its skin to emerge through a split in the back.  The remaining skin floats in the surface film and serves as a launching platform for the newly emerged dun to stretch its wings and begin its life in the air.

Dun to Spinner

When emergence occurs, air exposure quickly hardens the wings and skin and shortly the dun flies to nearby trees and bushes to await its next transformation.  The dun will again shed its skin after a half to a full days wait whenever the weather is optimal.  After again shedding its skin the dun transitions into the final stage known as the spinner.

Spinner to Egg

Swarms of male adult spinner mayflies form over waters that are optimal for hatching mature nymphs.  Female mayflies are caught in the air by males and mate prior to depositing their eggs.  Spinner swarms usually form 18-24 hours after the adult duns emerge and only last a few short hours.  The female mayflies then deposit their eggs on or below the waters surface by skipping on the surface or even occasionally diving.  Both males and females are quickly exhausted from the mating swarm and die on or near the water soon after.  The cycle begins again as the eggs hatch and mature.

 

Caddisflies

Caddisflies are often mistaken for tiny moths. But unlike moths, caddisflies have a distinct ten-like formation to their wings while at rest.  Getting a good look at a resting caddisfly can be a challenge due to the erratic behavior of most caddisflies.  Caddisflies outnumber the mayfly in numbers of species, and at least inhabit an equal number of aquatic environments.  Accordingly, trout eat caddisflies in large numbers.  Thankfully the erradic behavior of caddisflies is something quite easy for fly anglers to imitate.  The life cycle of caddisflies pass from egg, to larva, to pupa, to adult.

Egg to Larva
What Do Trout Eat - Caddis Larva - Fly Fishing Atlas

Caddisfly larva with an effective imitation

Adult female caddisflies drop their eggs, or directly stick their eggs to bottom structures by a process known as ovipositing.  After about two weeks the eggs will hatch into tiny larvae that settle in adjacent environments.  Caddis larvae ambitiously feed on plants and animals including tiny minnows and large dead fish.  Many caddisfly larvae build cases from sand or woody debris that protect them from injury and conceal them from predators. Though trout do eat case builder caddis regardless of their cases.  As the caddis grow, their cases are enlarged to accommodate their size.  Those caddis that don’t build cases conceal themselves on, under, and inside various bottom structures.  Of course, trout eat these free-living caddisflies, and these larval caddisflies also offer anglers the best opportunity for imitation.

Larva to Pupa
What Do Trout eat - Cased Caddis - Fly Fishing Atlas

A cased caddisfly hanging from the side of a rock. Notice the mixture of woody debris and sand.

When the larva has reached its full size it will build a case, if it does not already have one.  Like many butterflies and moths, the caddisfly lies dormant for a period in their case as it pupates.  The case is first anchored to bottom structures and then the caddisfly builds a door to close the case.  During pupation the caddis develops its wings and legs as well as the necessary anatomy to breath air and reproduce.  The pupa then waits until particular water conditions arrive before it will emerge as the adult.

Pupa to Adult

When light and water temperatures are optimal the pupa emerges from its case and either crawls on swims to the surface.  This is a vulnerable time for caddisflies and hungry trout eat the pupae whenever possible.  But adult caddis pupae are often quick swimmers and can emerge from the water quite quickly.  The outer skin of the pupa inflates and separates from the pupa at the time of emergence.  The air-filled shuck adds to their natural buoyancy and helps the caddisfly ascend to the surface.  Trout eat these emerging pupae during their ascent or on the surface if they can catch them.  But the fast emergence often leads to plenty of splashy rises during intense caddis hatches.

Adult to Egg

The adult caddisflies congregate among the nearby vegetation and begin mating flights that last a few weeks.  Caddisflies tend to favor the most enjoyable times of day to make these mating flights and deposit their eggs.  Adult caddisflies are still remarkably capable on or in the water.  Female egg-laying caddis will often crawl or swim under the water to oviposit their eggs in ideal locations.  Because the mating flights last a number of weeks, trout eat them almost all summer.  For this reason, a good variety of adult caddisfly imitations are an excellent tool for anglers to query unfamiliar waters.

 

Stoneflies

What Do Trout Eat - Adult Golden Stonefly - Fly Fishing Atlas

The stonefly is an important insect for anglers to understand.  They require relatively clear and clean water that contains high levels of dissolved oxygen.  Stoneflies cannot breathe with the same level of efficiency as other aquatic insects and often depend on flowing water to pass oxygen through their gills.  With that in mind, slow flowing streams and lakes do not often harbor large numbers of stoneflies.  The stoneflies need for high quality water can also be a good indicator for suitable trout habitat.  Stoneflies have three major life stages: the egg, the nymph and the adult.  But the stonefly life cycle is long, with generations ranging between two to four years.

Egg to Nymph
What Do Trout Eat - Nymph Golden Stonefly - Fly Fishing Atlas

Golden Stonefly Nymph

The Adult female stonefly deposits egg clusters just below or on the water’s surface.  The egg clusters break-up, sink, and hatch over a very large time span.  Some species hatch in a few days or a few weeks, while others can almost take a year.  Regardless, the eggs and the very tiny nymphs that emerge have no real significance to anglers.  But as they grow the stonefly nymph becomes a significant food source.

The small stonefly nymphs settle in the choicest locations for the sake of feeding and their need for highly oxygenated water.  Some species eat only plant life while others are highly predacious.  Stoneflies compete for foods and territory, and consume other aquatic insects and newly hatched fish fry.  Stonefly nymphs shed their tough outer skin multiple times to facilitate their growth.  Due to their unique characteristics, it is fairly easy to avoid confusing them with other aquatic nymphs.

Nymph to Adult

Mature stoneflies pass directly from nymph to adult.  When the time is right, the water temperature and sunlight cue the larger species to crawl to shore.  The emergence usually occurs at night and will sometimes continue int the early morning hours.  The mature stoneflies pull themselves onto exposed banks, logs, and rocks where they split and shed their nymph skin.  The newly emerged adults require a period of drying before their wings and skin hardens.

Smaller adult stoneflies will often emerge right on the surface in a similar fashion as mayflies and caddisflies.  The small stoneflies shed their nymph skin and stand on the surface film to dry their wings.  These mid-stream emerging stoneflies can easily go unnoticed due to their flat profile.  They can also be masked by mayflies and caddisflies emerging at the same time.

Adult to Egg
What Do Trout Eat - Adult Golden Stonefly - Fly Fishing Atlas

Adult Golden Stonefly

The adult stonefly is most often concealed in streamside bushes and trees and rarely flies.  The adults mate out of reach from the hungry trout.  But once the females have mated they begin egg-laying flights back and forth to the water.  But stoneflies are not graceful pilots.  The egg-laying females often appear to crash land and skitter across the water causing quite the obvious attraction to trout.  The waiting trout eat the clumsy adults with wild excitement and ambitiously gorge themselves on the sizeable bugs.

Over a period of one to two weeks the adults deposit their eggs and eventually exhaust themselves, unable to fly from the water’s surface.  Hungry trout gobble up the fatigued and drowned insects, and the stonefly life cycle begins again with the newly deposited eggs.

 

Midges

Midges are more widespread and important to trout than most anglers know.  Their mosquitoe-like appearance often adds to the mistaken identity of these tiny insects.  In fact the order of Diptera includes mosquitoes, craneflies, gnats, and midges.  Midges hatch continuously from early spring to late fall, and inhabit a range or water conditions that are well beyond what trout can tolerate.  It is very likely that trout eat more midges than any other aquatic insect.  Midges can be frustrating for anglers to attempt to imitate due to their small size, which is often size 18 or smaller.  Midges have life stages much like the caddisfly in that midges pass from egg, larva, pupa, to adult.

Egg to Larva

Once midge eggs hatch the larva take up residence in the surrounding structures of the lake, river, or stream.  Larva are very thin and appear much like a tiny worm.  Midge larva eat plant life and quickly grow to a size that interests hungry trout.  When swimming the larvae make whip-like movements that is very attractive to nearby trout.  The midge larva often sport bright colored reds, bright greens, gold, olive, yellow and black.

Larva to Pupa

When the larva is full-grown it will begin pupation.  Like caddisflies, midge species that live in flowing water will make a pupal case and attach themselves to the stream bottom.  In still waters the midge pupa will remain free swimming.  Within a few days the midge pupae quickly develop legs, wings, and their abdomen and thorax becomes enlarged.  Like the larval midge, the pupa will rise to the surface when they are prepared to emerge.  When waters remain calm trout can often be seen cruising just beneath the surface, often with their dorsal fin exposed, gorging themselves.

Pupa to Adult

When mature midge pupa rise to the surface they hang in the surface film with a very different posture than caddisflies and mayflies.  Instead, midge pupa hang vertically.  The pupa then splits its skin and emerges and extends its wings to dry and harden.  The emerging midges transition from vertical to a more horizontal orientation in or on the surface film.  The adults often clump together in small groups as they sit on the water’s surface.  It is an observable phenomenon that trout eat these groups rather than the individual insects.

Adult to Egg

Adults form mating swarms within one day after leaving the water.  The females return to the water to lay their eggs on the surface or slightly below.  Both male and females die shortly after mating but rarely fall to the water as other aquatic insects.  Because of this fact, the spent midges are not a significant food source for trout.  The life cycle begins again as the eggs sink to the bottom and establish a new generation.

 

Dragon and Damselflies

What DO Trout Eat - Adult Dragonfly - Fly Fishing Atlas

Adult Dragonfly

Dragonflies and damselflies are an incredible food source for trout.  And one that is incredibly neglected by anglers.  In lakes and ponds dragonflies and damselflies can reach nearly two inches in length.  These large insects not only provide a big meal, but they also live much longer in their aquatic and terrestrial forms than the previous four insect orders we’ve discussed.  Both dragonflies and damselflies life cycle passes from egg, nymph to adult.  While the life cycle of dragonflies spans two to four years, damselflies life cycle is one or two years.

Egg to Nymph

After about two weeks the tiny nymphs emerge from the egg.  Dragonfly and damselfly nymphs are active predators that vigorously pursue, kill, and eat any smaller aquatic insect or small fish.  The nymphs are very capable swimmers that prefer to crawl around structure like plants and roots to hunt their prey.  The nymphs are truly fierce predators in so much that they will even kill each other when possible.  For this reason they are not often found in concentrated numbers.  But because of their large size and tendency to fearlessly expose themselves, they present a captivating opportunity for big trout.

Nymph to Adult
What Do Trout Eat - Dragonfly Hatch - Fly Fishing Atlas

The empty nymph skin from a recent dragonfly hatch. Notice the split extending from the back of the head to the wing pads.

In the spring or early summer the mature nymph crawls out of the water onto nearby structures in order to dry and split it’s skin.  This emergence can take hours of effort and strain.  Once emerged the adult slowly extends its wings to allow them to dry and harden.  The abdominal structure greatly changes and elongates as well.  Within a twenty-four hour period the transformation is complete.  The newly emerged adults are very vulnerable as they are somewhat clumsy fliers and can end up back in the water and struggling to escape.  Those who successfully take-off will likely be entirely out of reach to trout until they return to lay eggs.  Some aquatic insects stop eating entirely once they emerge from the water, which only shortens their terrestrial lives.  But dragonflies and damselflies continue their active hunting and predation on other small insects and live very long terrestrial lives.

Adult to Egg

Adult dragonflies and damselflies form pairs to mate.  While dragonflies have wide ranges that often stray far over land, damselflies remain very near to water as adults.  Egg-laying dragonflies return to the water and skim the surface to deposit their eggs.  Damselflies land on weed beds and sometimes even crawl down plant life to deposit their eggs deep beneath the surface of the water.  The cycle begins again as the eggs hatch.  And due to their long life cycles, dragonflies and damselflies will have multiple generations of aquatic nymphs living in one body of water.