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Arthropod Class Insecta (Insects)

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Nearly a million species of insects have been described by entomologists. I have left several of them off of this site, just to save time, but I've tried to include all the main aquatic insects trout eat in North America.

This site focuses on aquatic insects, of which the most important are mayflies (Ephemeroptera) and caddisflies (Trichoptera). Stoneflies (Plecoptera) come in third, a position arguably challenged by the many two-winged true flies of the Diptera order, which includes midges and craneflies. I've also included some terrestrial (Terrestrial: Insects which live on land and are fed on by trout only when they incidentally fall into the water are known as "terrestrials" to fly anglers, and they're very important in late summer.) insects which I've found on or near trout streams. Terrestrials (Terrestrial: Insects which live on land and are fed on by trout only when they incidentally fall into the water are known as "terrestrials" to fly anglers, and they're very important in late summer.) like ants, beetles, and grasshoppers are an important food source for trout in many places, especially during the summer months.

Aquatic insects do not live their entire lives in the water. Instead, they grow for a year (give or take quite a bit) as nymphs or larvae underwater, and then they emerge into air-breathing winged insects for a short while to mate and die. There are many variations on this theme.

The most important aquatic insects for fly fishermen are mayflies, stoneflies, caddisflies, and midges. Mayflies and caddisflies are the most discussed by angler-entomologists, because it's so useful to closely identify them. The behavior of their species guides the behavior of feeding trout, and an angler who understands the lifecycle of a particular species has the upper hand when it's hatching. This is not so important for stoneflies and midges, because their hatching behavior is less variable.

Pictures of 1002 Insect Specimens:

Specimen Page:1234...101
Specimen Page:1234...101

1 Streamside Picture of Insects:

Callibaetis spinner on an alpine lake in Washington's Cascades, the one referred to by the alias of Upper Lake in my Golden Trout trip report.  In this picture: Mayfly Genus Callibaetis (Speckled Duns). From Upper Lake in Washington.
Callibaetis spinner on an alpine lake in Washington's Cascades, the one referred to by the alias of Upper Lake in my Golden Trout trip report.

In this picture: Mayfly Genus Callibaetis (Speckled Duns).
LocationUpper Lake
Date TakenSep 3, 2017
Date AddedSep 5, 2017
AuthorTroutnut
CameraNIKON 1 AW1

114 Underwater Pictures of Insects:

Underwater Photo Page:1234...13
Hundreds of cased caddisfly larvae live on this log in a small brook trout stream.  In this picture: Insect Order Trichoptera (Caddisflies). From Eighteenmile Creek in Wisconsin.
Hundreds of cased caddisfly larvae live on this log in a small brook trout stream.

In this picture: Insect Order Trichoptera (Caddisflies).
Date TakenApr 14, 2004
Date AddedJan 25, 2006
AuthorTroutnut
Several Baetidae nymphs line up on a rock.  In this picture: Mayfly Family Baetidae (Blue-Winged Olives). From Mongaup Creek in New York.
Several Baetidae nymphs line up on a rock.

In this picture: Mayfly Family Baetidae (Blue-Winged Olives).
Date TakenApr 19, 2006
Date AddedApr 22, 2006
AuthorTroutnut
CameraPENTAX Optio WPi
This is my favorite underwater picture so far. It shows a bunch of Simuliidae (black fly) larvae clinging to a rock and swinging in the fast current. There are also at least four visible mayfly nymphs, probably in the family Baetidae.  In this picture: True Fly Family Simuliidae (Black Flies) and Mayfly Family Baetidae (Blue-Winged Olives). From Eighteenmile Creek in Wisconsin.
This is my favorite underwater picture so far. It shows a bunch of Simuliidae (black fly) larvae clinging to a rock and swinging in the fast current. There are also at least four visible mayfly nymphs, probably in the family Baetidae.

In this picture: True Fly Family Simuliidae (Black Flies) and Mayfly Family Baetidae (Blue-Winged Olives).
Date TakenMar 19, 2004
Date AddedJan 25, 2006
AuthorTroutnut
Underwater Photo Page:1234...13

Recent Discussions of Insecta

Mayfiles other than Callibaetis 1 Reply »
Posted by Royal_Coach on Jan 15, 2018 in the genus Callibaetis
Last reply on Jan 15, 2018 by Millcreek
every book/article I read says Baetidae is the most imporant family and Callibaetis the most important genus of mayfly. Why? Does this just mean they are the most prolific? Am I not likely to encounter any other family/genus on a western river?
ReplyOld worn out trouter
Posted by Jimcar on Jan 14, 2018 in the species Ephemerella excrucians
Great site. Have been on here for more than two hours now and am fascinated by the info. Thanks!
ReplyPolymitarcyidae Question 1 Reply »
Posted by Steamntrout on Jun 22, 2017 in the species Ephoron album
Last reply on Jun 23, 2017 by Crepuscular
What size are these nymphs & Sub Imago's?
ReplySteamntrout
Posted by Steamntrout on Jun 14, 2017 in the species Leptophlebia nebulosa
Looking at Purdue's May Fly Central it shows nebulosa being found in Canada's Far North, North East and North West as well as USA's North East, South East & Far West.
ReplyClinger nymphs are shaped that way to hang in really fast currents. Really? 14 Replies »
Posted by Entoman on Feb 24, 2013 in the genus Rhithrogena
Last reply on Jun 14, 2017 by Steamntrout
It is commonly held that clingers are flattened to make their lives better adapted to faster water. Their teardrop shape is certainly a classic symbol of aero and hydrodynamic perfection, so there must be some connection, right? It seems to me that such ideas show a complete misunderstanding of the hydraulic reality in which they live. Current is negligable even in the fastest a few mm. from the surface of solid objects. In fact, it is actually quite calm. I've observed baetids clinging by their tippy toes to the tops of rocks in fast riffles with no apparent effort, often next to clinger species that look like they're hanging on for dear life. What if clinger nymphs are flattened not to hold their place in fast currents but rather to facilitate movement in their ecological niche of the cramped spaces under and between cobble or crevices in other substrate types?

It is also thought that the gills of some species form ''suction'' to hold them in place. Since suction is a phenomena of vacuum creation in the atmosphere, how are these nymphs accomplishing this underwater? Is it their ultra delicate gills that hold them in place or a firm claw grip? The horizontal sprawl of the legs masks this as the gills stay in place until the legs brake free. Exposed to the air, the gills seem to laminate against the rock, just as crepe paper would if first held underwater before a rock was lifted out into the air from underneath it. However, underwater their gills behave like the crepe, flowing freely. They are performing their function as gills not suction cups. I find it hard to believe they evolved the way some think merely so they can make it more difficult for humans to pluck them from rocks in the atmosphere. How is it these mighty structures that defy our attempts to pry them from the rocks curiously fall off so easily when prodded for inspection a few seconds later in a tray or jostled in a container on the way home?

Even many scientific papers have encouraged these dubious beliefs so it's not just angler myth... And they go unchallenged... Thoughts?
Reply
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