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Understating insects is the key to success

May 30, 2009
By Jon Magee

Last week I talked about mayflies and their importance for the fly angler, so this week I thought I would talk about more bugs that trout feed on this time of year. The next month holds some of the best fly-fishing of the year and there will be many different insects available for the fish. Proper identification of what the trout are feeding on and fishing techniques can be the difference between catching fish and just casting a fly.

Caddis flies, stoneflies, midges and terrestrial insects are an important food source in many local waters, understanding these insects will increase you enjoyment on the stream, and I will try to address most of them, I just hope its not too boring.

Caddis flies are abundant on most local streams and in fact are more numerous on many waters than the more popular mayflies, so it helps to have a simple understanding of these bugs and the way trout react to them. Caddis flies are important because they often hatch throughout the day, beginning afternoon and continuing until evening.

Trout are used to seeing them and the duration of their hatches can last up to a month or more so there is usually some type of caddis fly on the water at this time of year. Caddis are related to moths and look somewhat similar, they have no tails, and when at rest fold their wings over their backs to resemble a tent shape, and are erratic in flight.

Like moths, they undergo complete metamorphosis going from egg to larvae, and then form a pupa to develop into winged adults. Caddis range in size from the large October caddis (8-10 hook size) to tiny micro caddis (22-24 hook size), but most range in the 14-18 hook range. The colors also vary with tan, green/olive, cream, and gray the most common you are likely to encounter this summer.

There are two types of caddis, case builders and free-living caddis. As larvae, the case builders construct a protective case from vegetation, small pebbles, and/or sand. Some attach their cases to rocks or debris in riffles and runs where they can extend their bodies into the current and intercept passing food while others build cases that allow them to be more mobile and crawl around protected by their case as they search for food. Stick bait, as old timers often refer to it, is actually a caddis fly; if you open up the case, you will find a small wormlike larvae or pupa inside, the same with the small pebble and sand cases found on rocks only sometimes they are vacant after the fly has pupated.

These cases can be quite small or large depending on the species, trout do feed on the larvae, case and all, but the case builders are more available to the trout as pupa when they hatch into adults.

Free-living caddis larvae ( often referred to as rock worms) do not build cases but anchor themselves to rocks with silk and are most commonly found in riffles, if you pick up and inspect the underside of rocks you will often see these wormlike larvae attached.

They are typically small (14-18 hook size) and range from bright green in color to more drab grays and olives with a brown or black head and legs. These larvae are a consistent food source for the fish and a green rock worm fly can be very effective fished in the riffles and runs when there is no surface activity.

All caddis flies form a cocoon to pupate and after a week or so transform into winged adults. This is when they break free from the safety of their case and is most vulnerable to the fish; trout will gorge themselves on the pupa as they ascend through the water column to free themselves from this cocoon near the surface. Unlike mayflies that often need to drift for some distance on the surface to dry and pump blood into their wings, the caddis fly can inflate their cocoon, which helps buoy them to the surface, where they break free of the cocoon and fly off after a few wing beats. This can create some of the most exciting fly-fishing you are likely to encounter and paying attention to what the trout are telling you by how they are feeding can really pay off.

Splashy rises usually mean trout are feeding on caddis, either adults on the surface as they flutter their wings or the pupa just beneath the surface. It can be difficult to tell the difference but trout are very efficient and if you do not see the snout above the water it a good bet the fish are taking the pupa.

When there is a heavy hatch of caddis, the trout will sometimes feed almost exclusively on the emerging pupa, the pupa travel up through the water column until they hit the surface film where they must break the surface tension before they can fly off. The fish will key in on this and it will look like the trout are taking dries but will actually be feeding on the emerger just under the surface.

A good tactic for this is to fish a pair of flies; either an elk hair caddis with a sparkle pupa dropper or two wet flies can be deadly in this situation. Since caddis flies are very active as they hatch, adding a little movement can often be better than a strict dead drift.

If I am fishing to trout taking caddis, and they refuse a dead drifted dry with a pupa dropper I will twitch the flies as they pass where I saw trout rise, just a couple inches can draw some vicious strikes. An elk hair caddis in the appropriate color of the natural works great for this since it is easy to skitter over the surface with its bushy hackle, which looks and behaves naturally.

Once hatched caddis will seek shade and rest in the streamside vegetation, they are often seen flittering about under pines and other shady overhanging brush over the water. The trout know this too and will lie in wait beneath the brush for a fly to make a mistake and hit the water, for this reason it is a good idea to place a few casts under overhanging brush especially if the water is more than a foot deep. Caddis flies live for a week or more as adults before mating and laying eggs, and this is when the flies are once again available for the fish.

Most mating and egg laying activity occurs in the evening and depending on species the egg laden female will dive beneath the surface, skitter across the surface or just land on the water to deposit her eggs. If you capture a few adults in the evening, you will notice the egg sac on the females, often a bright green but the color varies. I like to tie a few caddis with egg sacs and no hackle to represent the females and they can work very well at times, but standard caddis imitations will also work. The no hackle pattern also works well for the females that dive to release their eggs but wet flies are hard to beat and a simple dark cahill, leadwing coachman, or partridge and green can work wonders.

This is just an overview but as you can see, there are many relationships between bugs and trout, some complex and some simple. There is nothing more frustrating than standing in a stream watching trout rise all around you but you get no response from your best flies and presentations. Remember a rising trout is a catch able trout, however even though your fly may look exactly like the insect the trout are feeding on, a trout may not eat it if it does not behave like the natural insect.



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