Insects make up the diet of an amazing diversity of animals. Frogs, toads, salamanders, small mammals, many bird species - and of course trout - depend on a diet of insects for their survival.
Insects, of course, don’t appreciate being eaten and have evolved many ingenious adaptations to protect themselves from predators.
It has often been said that to become a great fisherman, you have to learn how to think like a fish. Maybe what you should really be doing is thinking like a bug - like the insects the trout depend on to survive.
To avoid detection by predators, insects are cryptically colored, they expose themselves as little as possible, and they inhabit places that best match their camouflage.
So if you are fishing a big, brown dragonfly nymph over a lush green weed bed, or black stonefly pattern, over sand colored rocks, you are not likely offering the trout what they are naturally likely to see. If you aren’t thinking about the background, and about the importance of camouflage to insects, you aren’t going to match the hatch.
The vast majority of aquatic insects are camouflaged to blend into the environments they choose to inhabit. Shades of yellows, browns, grays, and blacks are the dominate colors in coastal valleys of British Columbia, where I fish, and not
surprisingly they are also the most common colors found in insects.
Adults, pupae, and insect larvae that spent most of their time among yellow-green leafy foliage will tend to be yellow-green in color; those insects which spend most of their time on bark, dead twigs, or on the ground tend to be gray, brown, or black.
Bands, patches, and stripes serve to disrupt wing and body shape, making insects harder to see. The undersides of most insects is invariably lighter than the upper side a phenomenon known as countershading. The shape of some insects even resemble objects around them such as a leaf, a lichen, a grass blade, a conifer needle, a twig, and so on.
Some of these resemblances are surprisingly exact. The jagged wing undersurface of Anglewing, Mourning Cloak, Tortoise Shell, Painted Lady, and Admiral butterflies, for example, look like dead, dried out leaves. The difference between moths and butterflies simply reflects the fact that butterflies tend to rest with their wings folded up together (the undersurface exposed and upper surface concealed), whereas moths tend to rest with wings laid down flat (undersurface concealed and uppersurface exposed). The green and brown caterpillar of the hawk moth resembles a crumpled leaf with brown patches. Some caterpillars will even bite out strips of a leaf margin and then rest so as to fill in the missing piece!
The larvae of many conifer feeding insect species are striated, to resemble the needles. The caterpillars of the grass eating Satyr butterflies have patterns of thin contrasting lines or stripes which enable them to blend in with the long, thin grass leaves they feed on. Many of the Geometridae moths - the "inch" worms - looks just like dry twigs. Maybe it’s not surprising, then, that we sometimes see trout rising to take bits of wood off the surface, as if they were insects.
Insects also engage in many kinds of behaviors which make them less available or inconspicuous to predators. One such behavior is to remain in the environment which best matches their coloration. Studies suggest that dark moths "deliberately" seek dark areas and large moths light areas, for example. Should we expect dragonfly nymphs to be any less cautious? Might the brown shaded fly that works in one bay for trout, be completely out of place in another part of the lake, where the vegetation color is slightly different?
If you watch a butterfly after it has landed, first it folds its wings together up above its back; then it often leans sideways - sometimes quite considerably. It is believed that this subtle behavior reduces shadow formation, which in turn makes the insect less visible to predators.
Insects which are well camouflaged, and keep still are obviously going to be more difficult to see. So keeping still is an important defensive strategy of insects.
Many fly fishermen - especially in still waters - think they aren’t fishing unless their fly is in motion. In fact a dead drift is often the only thing that makes sense.
Some insects become immobile only when threatened by predation - that is,
they play dead. Every child is familiar with how the Woolly Bear caterpillar
curls up into a tight spiral when roughly handled and stays immobile for
what seems an eternity.
Hiding, presumably is a particularly good way to conceal oneself from a predator. One common insect behavior is to forage only at night or during low light conditions, and hide during the day. For example, some caterpillars hide under leaves during the day time, and come out to feed at night.
Some insects even build their own hiding places or shelters. Some shelters are simple - like the folded or rolled over edges of a leaf. Other shelters, like that of the caddisfly are made of stone and are incredibly durable - the shelters will last long after the insect who made it has died.
Once the predator has detected potential prey, it must determine whether or not it is worth expending energy of trying to attack and kill it. Predators will avoid "dangerous" foods; that is, insects that may cause pain or make them sick. Some insects even advertise the fact that they are poisonous "unprofitable" prey. Interestingly enough, trout do not hesitate to take insects - like wasps - that we tend to be afraid of. Are their mouths immune to a hornet’s sting? Or do they know they can snap them up without being stung? Or is it simply that they see bees and hornets so rarely that they forget they are stingers? Certainly fly fishermen know that a trout once stung with a hook is unlikely to come to the same pattern again for quite sometime. But eventually, the trout will rise again. However, often this occurs when you are fishing a pattern that resemble a non-stinging insect, like a Mayfly. The trout knows it won’t get stung by a Mayfly - but it has been. So it sulks, then tentatively rises again....then begins feeding once more with confidence. That’s when you get a second chance.
After the predator has made the decision to capture an insect, it is up to the insect to detect the approaching predator, and escape.
A good way to increase the odds of detecting an approaching predator is to forage in groups. Presumably this is one of the reasons why birds flock together in wintering feeding groups; why butterflies can often be seen feeding together around mud puddles - and why salmon fry migrate in schools.
Many species of moths have highly sophisticated hearing organs which can actually detect the the ultrasounds emitted by bats in search of prey. Studies show that as soon as these moths detect the bat's ultrasound they go into an erratic flying pattern.
Another good way to escape from predators is to simply "out-run" them. By imitating flight, with a fast, jerky retrieve when fishing a fry pattern, you can often trigger pursuit from trout and salmon. Fishing at the mouth of a Vancouver Island river one fall, I found the only way to get coho to strike was to strip in a herring pattern as fast as I could.
Lastly, it is worth pointing out that another insect "defense" strategy is to simply produce lots of oneself. That strategy has led to the hatch, when insects come off in profusion. And the hatch, as we all know, created fly fishermen - which perhaps is the insect’s way of getting revenge on all those hungry trout.
