The simplest form of streamside sampling is done by picking up and looking at submerged rocks. Choose cobblestone-sized rocks that are easy to lift. Under close inspection, you will find that most rocks have a number of insects crawling or clinging to their underside. Take one of the insects and examine it in the palm of your hand. Right off the bat, even if you don’t know what type of insect it is, you can see its size, color and profile. Already you have a starting point, as long as you have a decent match in your fly box. Do this for each different insect found on the rock. Keep in mind that just because one type of bug is predominant in the sample, it doesn’t exactly mean that’s what the trout are keyed in on – it may take some trial and error. After examination, let the buggers go and replace the rocks as you found them.

A more thorough stream sample can be taken by a method called seining. A seine net is an effective and inexpensive tool that won’t take up too much room in your vest or chest pack. They can be purchased at your local fly shop for usually around $20. An angler’s landing net can be used as a substitute, as long as the mesh holes have small enough diameters to not allow tiny insects to pass through during sampling. A handy person can even craft their own seine net at home by cutting a flexible window screen to size and attaching two wooden dowels. The one I use, a Wind River Handi-Seine, is made from pliable screen material that rolls up nicely for storage. On either end are sleeves from which extend wooden handles. In the middle of the dark net is a painted white circle, which serves as a visual aid while identifying your sample. The whole package weighs only two ounces.

For a good seining location, walk upstream from where you plan to fish, so as not to spook any feeding trout. If alone, stand in a shallow, rocky riffle facing downstream. Place your seine net snug to the stream bottom. Using your feet, shuffle the rocks and gravel upstream of your net. The shuffling motion will dislodge aquatic insects from the rocks and the flow of the water should guide them into your net. If you’re with a partner, stand just downstream holding the net and have them kick up your sample. After a few seconds of this, take the seine net to the stream bank and begin scanning for food items.