All About Trout Diets: Insects as Feed Preference

All About Trout Diets: Insects as Feed Preference for Trout

In California and other regions of USA trout fishing, the angler who fishes many streams and lakes will find an astounding variety of different aquatic and terrestrial insects. Because most stream systems have their headwaters at very high altitude.

And these flow down a vertical drop of about 10,000 feet, the angler is faced with the job of imitating insects of many kinds even in a single stream.

All About Trout Diets: Tips for Anglers

The many reservoirs further complicate the problem of duplicating insects in trout diets. Some insects will live only in still waters of reservoirs. Other species live only in flowing water:

Observation for Trout Fishing

It should be obvious to any trout fisherman that if he is on a section of stream or a lake when a big hatch is coming off the water, he should try to duplicate the insect the trout are feeding on. It would be silly to use a dark pattern when a pale mayfly is coming off the water.

More than color, however, the size of the fly is the critical element. Good observation of all factors influencing what the insect population is doing will pay off for the angler. These particulars are covered in detail in many books on trout fishing. In California waters, the only difference is the multiplicity of insect populations due to the variations in altitudes and the types of water available.

If you are a student of insects there is a very good book on the subject, “Aquatic Insects of California.” edited by Robert Usinger, University of California Press. This is a general guide to California underwater insects and is not limited to trout feeding habits.

Fair Fly Tier to Imitate Easily

We’ll deal here with only a few insects that it is possible for a fair fly tier to imitate easily.


Most presentations on fishing with flies usually start with a discussion of mayflies. I feel the stonefly and caddis fly are more important in our waters. Nearly every stream system in the state has both stonefly and caddis flies. There are plenty of mayfly hatches in California but I want to point up the importance of the other two species in the diet of California trout.

Life History of Stoneflies

Life History Many of the stonefly hatches occur in late spring and early summer but some occur even during the winter This makes stoneflies and their larvae a year-around item in the trout diet. Some of the hatches, called “salmon fly” hatches, can be spectacular.

These large flies only occur in a few places. The less spectacular stonefly hatches can be made up of very small individuals.

The female generally lays her eggs much as mayflies do, by flying along and dipping her abdomen on the water while in flight. This can be spectacular because of the size of the flies and because stoneflies are notoriously poor flyers.

When the larger females begin laying their eggs, they often hit the water with an audible splatting noise. This is important when fishing streams that have hatches of large stoneflies.

Creating a Stoneflies Hatch

You can often create a hatch of your own by splitting large flies on the water, even if there have been no significant hatches for a long time on that particular stream. Trout tend to ignore any fly that isn’t splatted on the water when they are feeding on an actual hatch.

Stonefly Nymphs

The nymph stage of the stonefly is the most important to the angler. It is very likely that popular flies like the Wooly Worm are taken by trout because they do a passable job of imitating the larger stonefly nymphs. The actual nymph is not free-swimming and to imitate them correctly a fly should be fished deep and slow.

When the stonefly is ready to mate it crawls up on rocks or stems of water vegetation. It rests a distance out of the water until the adult emerges.

After waiting to dry the adult flies to streamside brush. Some nymphs undoubtedly get washed away in the current where trout can take them without plucking them from the rocks as they climb toward the surface. A free drift, slow and deep with a few twitches, will properly imitate this situation.

Caddis Flies and Sedges

Caddisflies are on hand in nearly every freshwater lake or stream in the USA. The American sedges, a form of caddis, are the flies you see swarming near almost every trout stream during the warm months. They “dance” over the surface of the water in swarms and are often thick in streamside vegetation.

Life History Caddis Flies and Sedges

The female caddis deposits her eggs in or near the water, usually by crawling underwater. The larval form is the all-important case worm so familiar to most fishermen. The larvae build their tubes from bits of stream or lake bottom material, using bits of wood, leaves, and stones which they cement together to form the protective covering they need.

These tubes can be plucked off stones in quiet backwaters of streams and used for bait. They can be fished case and all or the larva can be taken out of the case. If you check the stomach contents of trout you’ll often find bits of stone and wood. This comes from eating caddis worms, case and all.

Imitate them Properly

Most of the life of the caddis larvae is spent in contact with the bottom. To imitate them properly a fly should be fished slow and deep.

A majority of caddis flies I’ve checked have gold or cream bodies, with heads and legs of dark brown or black. A good fly can be tied to represent these larvae with very sparse and dark hackle.

The proper size can be found by merely pulling a few caddis cases from the rocks and checking the size of the actual larvae. The combination of the right color and size will nearly always give a good measure of success.

Using them for Trout

Understanding the trout feed is important to catch them with the line and reel. Though I doubt trout see caddis larvae out of their cases too often, they will hit flies of the right size. The size that represents the worm inside the case. I’ve experimented with flies tied to indicate the caddis case. Also, I’ve fished by rolling along the bottom, but with poor results.

A fly tied with a few feathers flat across the back of the fly will yield some good trout if it is fished in the surface film of the water. Though adult caddis is not nearly as important as the larvae in trout diet, they often fall to the water, and dead females are washed downstream.

Trout recognize them and flies that imitate them. The adult caddis can be identified when at rest by the wings folded like a tent over the body. The adult stonefly, in contrast, lays its wings flat across the top of the body.

About the Author Alex N. Ferroni

About me: Hi, I'm Alex N. Ferroni, One of the creators of The Safariors blog and former camping trainer at Tripspot Magazine. I wish some other outdoor, hiking, hunting, fishing and camping enthusiasts have made this blog to share our thought. We are learning a lot through each trip, and we want you to learn that too!

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