Now that you have a glimpse into the aquatic life of your river, it's time to turn your seining results into fishing results.   To do this you'll need some basic observations to assist in on-stream fly selection, your fly-shop purchases and your time at the tying bench.  Here are a couple key areas to look at with some photo examples.

Size & Proportion:  The most obvious aspect of the insects you'll observe is their overall size.   In some rivers you will find everything from a size 2 to 22.  Look for size ranges within a specific type of insect.  Are all the mayfly nymphs a similar size, or is there a range?  Consistent sizes let you narrow down your choice of flies, otherwise, you'll need to experiment.

Also pay attention to the length and shape of the key body parts.   In fly tying we pay particular attention to the tail, abdomen, thorax, legs and antennae.

• All of the insects shown have very prominent legs.  Mayfly legs are up by the thorax and may hang down or stick straight out.  Scuds have legs from head to tail !!
• Notice the thick thorax on the mayfly nymphs,  matched nicely to Hare's Ear's and Pheasant Tail patterns.
• Segmentation is a defining feature on many insects, but differ between species.  Caddis larvae have rounded segments, while Stoneflies have a very flat segmentation.
• Mayfly nymphs have three prominent tails, stoneflies two, and caddis usually just a tuft of fuzz and anal hooks

Color & Texture:   Some insects are uniform in color, top to bottom and head to tail.  Others have very different colors on their backs, undersides, legs & wingcases.  Shiny & smooth surfaces suggest different tying materials than flat colors, rough surfaces or segmentation.  Flashback may be perfect for the mayfly wingcase or scud shellback, but for the stonefly or mayfly crawler dubbing & a section of feather would work better.

Population %:   A typical seine sample on one of our local rivers may pull up 4-6 stoneflies, dozens of mayfly nymphs and some caddis larvae.    The mayflies easily outnumber everything else but are certainly smaller than either stonefly nymphs or caddis larvae.

The key is to understand the population percentages currently in the water so you can build a hit list of flies to try.  A good place to start your fly selection is with food that is either plentiful or BIG !! Your collection results will indicate size, color and proportion.    In this case, maybe a stonefly nymph with an appropriately sized & colored mayfly dropper.

Lifecycle Stage:  This one may seem obvious, but it's more tricky than just nymph vs winged adult.   Take enough samples and you'll start to notice small differences in the insects as they go through different stages.   Nymph wingcases will grow longer as they near hatching.  The outer layer of skin may become more see-through affecting the color of imitation required.  Can you tell the difference between a dun & a spinner?  You may even find insects during emergence that would dictate a whole different set of patterns.

Insects at different stages also behave differently in the water.  We're all used to dead-drifting nymphs, but during emergence it may be more effective to float a fly in the surface film, or attach a soft-hackle dropper that rises from the bottom at the end of your drift.

Notes:

Trying to determine which of these attributes is most important to your on-stream success is always an entertaining discussion among flyfishers.  The suggestions here barely scratch the surface of adjustments you can make in fly tying, selection and presentation based on seining results.  But at this point you'll have some good information to help get started.