Fly Fishing Aquatics

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Other Aquatic Critters

Drawings and article by Ron Newman

Many of the so-called 'aquatics' are only found in ponds, swamps, marshes, and pools rather than on the open waters of our trout lakes.

Black flies, Crane Flies, Mosquitoes and so on, are aquatic, but not of much importance to the fly fisher. Often these only become a trout food when an adult accidentally falls into one of our lakes or streams.

Others, such as the snail or daphnia are a fairly regular food source of the trout. All together, these miscellaneous aquatic critters comprise about 8% of the feeding samples for trout in our lakes. Although this is a significant portion of the feed, most are still not important to the fly fisher.

Aquatic Worms:

Leeches, Horsehair Worms, and various aquatic earthworms are found in our lakes. Leeches (Annelida Hirudinea) are discussed in another section on this site. However, it should be noted that leeches comprise slightly more than 1% of a trout's seasonal diet.

Sometimes other aquatic worms can be mistaken for leeches. Some aquatic worms also possess suckers or mouths that look much like the leech. If it has suckers on both the front and the back end, you can be fairly certain it is a leech.

The Horsehair Worm is an interesting looking critter. It is very long (up to two feet in length) and very slim and looks much like the hair from a horses tail or mane. It swims much like a snake but is often found inter-twined with itself or other horsehair worms in a ball. As a larva, they are an internal parasite of various insects.

The Horsehair Worm belongs to Nematoda and these do not have body segments. Although the trout may feed on these, I have not yet found one in a feeding sample.

The aquatic earthworm also belongs to Annelida and is segmented like a leech. There are more than 200 species of aquatic earthworm in North America. Many species look like the terrestrial earthworm, but many also have hairs or bristles on their tail for swimming. Most feed on the bottom muck but some are predacious. I haven't found these in trout feeding samples in our lakes but they would digest very quickly and be hard to identify.

Clams and Mussels:

Clams and Mussels (mostly just called clams) belong to Mollusca and can be found in some of our lakes and rivers. These are shelled bi-valves. Because they burrow into the bottom substrates they are not often obvious to the fly fisher. On some lakes in the Prince George area I have had clams (or mussels?) actually attach themselves to my fly line or leader when retrieving along the lake bottom? The line passes through the open shells, the clam closes because of the disturbance and it becomes attached to the line.

On the Thompson River and other major river systems, clamshells can often be found along the banks and shorelines. The ancient Indians harvested clams. If you see shells buried in the bank, they are often indicative of an archeological site.

These mollusks are not restricted to Prince George or our rivers. I have found these in feeding samples on some of our pristine, clear water lakes. For example, I have found very small clams in feeding samples from Knouff Lake several times. The largest of these was not more than a quarter inch in size but I was quite surprised to find them. I have to admit that I didn't check these closely and it is possible that they were actually "clam shrimp" (Conchostraca). I promise to do a proper check on sample next time to be sure what they are.

Crane Fly:

The Crane Fly is a Diptera (two-winged fly) and is a larger cousin of our Chironomid. These are also called Leather Jackets and I grew up calling them Mosquito Hawks. They look like a very large mosquito. The larva and pupa are usually found in marshes or along the shoreline rather than the deeper water of the lake. Adults are only near the water for laying eggs. However, if an adult were to fall in the water, I'm fairly sure a waiting trout would snap it up.


Many Caddis, and the larva of other species, are often incorrectly called Hellgrammites. The true Hellgrammites belong to the order Megaloptera, which contain the fishflies, dobsonflies and alderflies. Most of these are called hellgrammites by the fly fisher. They generally tend to live in running water but at least one species is found in our lakes.

The adult looks much like a Stonefly. The larva of the species I have seen in our lakes has a wicked pair of pincers on its head for snaring prey. I wouldn't pick it up and can understand why the fish don't feed on it. I have heard that some of the stream species are not quite so veracious and are actually considered a food source for the trout. Can't prove it by me. However, from the species I saw in our lakes I know why the 'hell' is in their name.


The mosquito is a Diptera and closely related to the Chironomid. I often hear fly fishers say they are using a 'mosquito' pattern when flyfishing. If the fly is proving successful, it isn't because the fish are taking it as a mosquito. It is more likely being taken as a Chironomid. The mosquito (Culicidae) is not a common food source for the trout.

The mosquito must obtain its oxygen directly from the atmosphere. It does this through a siphon tube that it extends through the surface tension of the water. It then draws in air through the tube. If wave action occurs, it will likely break this surface contact and drown the mosquito. Because of this, these insects are restricted to marshes, ponds, swamps, puddles and pools that don't have wave action. They are not normally found on our interior fishing lakes.

Semi-Microscopic Organisms:

There are quite a number of organisms in the lakes that are almost microscopic in size. Although very small, these are often consumed by the trout and appear like mush or tapioca in a feeding sample. The total group was found in 4% of the feeding samples examined. I don't usually distinguish one type of 'mush' from another but will provide some of the more common types of semi-microscopic organisms for those interested.

  • Copepods - These small critters are related to shrimp and look like a comma ( , ) in the water. They are sometimes referred to as fish lice but only one genus is actually parasitic on fish. Most are free swimming and are fed on by trout, particularly the smaller fish. They can occur in great numbers at certain times of the year.
  • Daphnia - these are also called "water fleas". These look like a small dot in the water with antennae. They are closely related to the Copepods and Shrimp and are found in most freshwater environments. The trout feed on daphnia more frequently than Copepods and I have even found these in the feeding samples of larger trout. They tend to migrate upward in the water column in the evening or after dark and downward in the daylight.
  • Fish Lice - These are related to Copepods but are generally a little bit larger. They have four pair of swimming legs and attach themselves to the gills of a fish and feed on their host's blood. It takes a very close examination to see these on the gills of a fish. Fish that are 'jumping' rather than 'rising' are often said to be shaking these lice from their gills.
  • Water Mites - These are related to spiders. However, the larva only has six legs and it is not until they reach the adult stage that they have eight legs. The fly fisher is most likely to observe the red water mites on our interior lakes. They look like a small red dot with legs in the adult free-living stage. The larva is parasitic on insects or other aquatics (caddis, dragonflies, boatmen, snails, mussels, shrimp, etc). The mites don't tend to congregate in large numbers and so are seldom found in feeding samples.

Snails and Limpets:

Like clams and mussels, snails and limpets belong to Mollusca. However, they are uni-valve, rather than bi-valve. The single shell of the Limpet usually spirals in a cone shape while the true snail usually has the shell spiral outward from a central point (do-nut shaped without the inside hole). Both are generally called snails. The shells are made of calcium carbonate and so these are found in more abundance on the lower elevation and alkaline lakes, rather than the higher elevation and acidic lakes.

Trout will feed on snails and limpets throughout the open water season. They comprise almost two percent (2%) of the feeding samples, which is significant, but because their movement is "slow as a snail" they are not a food source that the fly fisher will often imitate. Besides, those fish feeding on snails often get the muddy taste associated with algae.

Water Beetles:

The aquatic or Water Beetles are a part of the order Coleoptera just like their terrestrial relatives. There are over 1,000 types of beetles that spend a part of their life in the water.

Most of the water beetles prefer ponds, swamps or the marshy area of lakes as opposed to the open waters of a lake.

The pupa of most water beetles are hatched along the moist shoreline rather than in the water and most adults rely on atmospheric oxygen for breathing.

The Dytiscus beetle is a predaceous diving beetle that may sometimes be encountered and has a very large set of biting jaws. The Whirligig Beetles are sometimes seen in a group on the water surface. These swim erratically, often in small circles, and will dive when disturbed.

The small scavenger beetles are the ones you will most likely see when launching your boat. These are usually small, black, have the typical oval shape of a beetle and usually dive into the bottom muck when disturbed.

Most of the water beetles are not of much importance to the fly fisher. Only on a few rare occasions have I found any water beetles in the feeding samples and these were the small scavenger beetles. I suspect they were accidentally ingested as the fish was feeding on something else.

Water Bugs:

The order Hemiptera is the Water Bugs and includes the Waterboatman (see section on this site). Most of the water bugs are highly predacious. Most can deliver a good bite or sting and for that reason the trout tend to avoid them. The trout often consumes the few species, like the Waterboatman, that don't bite or sting. Quite a number of the water bugs almost look like water beetles at first glance. Some of the more common water bugs are described below.

  • Backswimmer - If you have ever been stung by one of these in your swimming pool, then you will understand why the trout stay away from these. The life cycle and appearance is much like the boatman except it often swims or paddles through the water 'up-side-down' and are usually larger than a boatman. Only once have I found these in a feeding sample and I'm sure that was a mistake.

  • The Giant Water Bug - These can get over two inches in size, are highly predacious and very vicious. They will bite the toes of someone swimming and have even been known to attack newly hatched ducklings. If you have ever seen a large beetle-like bug carrying more than 100 eggs attached to its back, then you will know what the Giant Water Bug looks like.

  • The Water Strider - or Water Skaters, or as I call them, the Water Skipper. These are the guys with the very long legs that sit on the water surface and skip along in short bursts. They only appear to have four legs but actually have six. They seem to frequent the high elevation acidic lakes more than the lower elevation alkaline lakes. They are predacious but I don't know of anyone who was ever stung or bitten by one. Even so, the trout tend to avoid them unless food is scarce. Maybe they just taste bad??


Be sure to read other articles by Ron Newman

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