TROUT TREATS OR ESSENTIAL FOOD?

Terrestrials haven’t been ignored by fly fishers, but they haven’t been widely embraced either. Every summer, every major fishing magazine runs an article or two to remind us that mayflies and caddisflies aren’t the only thing that trout eat. Terrestrials, we’re reminded, are the chocolate chips of the trout’s world. After reading such articles, I dutifully go forth and tie some of the latest ant or beetle patterns and put them in a corner of a fly box. Too often that is just where they stay, until, sometime after the fishing season, I find them again buried in my vest.

But are terrestrials more than just tasty treats for trout tired of eating the same old Pale Morning Dun for lunch? It’s possible that terrestrials provide essential protein at a critical time of year for trout growth.

Besides the life cycle of each individual species of aquatic insect, there is an overall annual pattern to the abundance of insect life in a stream or lake. In general the peak abundance of aquatic insects occurs during the winter months. Eggs, deposited during the mating flights of spring and summer, have mostly hatched by late fall, causing a significant jump in the number of small nymphs and larvae. At the same time winter weather is dropping water temperatures quickly. Still, even at near freezing temperatures, most young insect larvae feed and grow slowly throughout the winter. Trout, during cold winter weather, feed less and grow slowly or not at all.

When water temperatures begin to rise in late winter and early spring, trout and insects alike begin to feed and grow more quickly. This is when there is a plentiful supply of food for fish in most trout streams. Aquatic insects continue to be abundant through the spring and early summer as insect emergence reaches a peak of activity. This provides a plentiful food supply for trout as their feeding activity continues to increase with warming temperatures.

In many temperate trout streams, July and August marks a change in the amount of aquatic insects available to trout. Though water temperatures may be ideal for trout growth, the majority of aquatic insects have emerged and their eggs lie quietly on the stream bottom. It is precisely during this mid summer period, when aquatic insects are sparse and fish are most active, that terrestrial insects peak in abundance. As a result, in many streams throughout the country, terrestrial insects become a significant component in the diet of trout when trout are growing the fastest and can best utilize a rich source of protein.

The Big Three

The diversity of terrestrial insects is far greater than their aquatic cousins. Given this wild array of life, unmatched by any other group of animals on the planet, three groups of terrestrial insects standout as king when it comes to food for trout: ants, beetles, and grasshoppers.

Ants

Ants make up the family Formicidae in the order Hymenoptera (ants, bees and wasps). Hymenoptera is one of the largest orders of insects; over a hundred thousand species occur worldwide. There are more than 15,000 species of ants worldwide, and approximately 700 species are currently known in North America. Ants occupy every conceivable habitat. Take a little time to look closely wherever you might be outdoors (or indoors!). It has been my experience, that with rare exception, there are ants. Whether it is in the middle of a shopping mall parking lot or the bank of a stream, ants seem to be present, following their queen’s marching orders with unyielding dedication that would make any Marine proud – Be all that you can be, join the Formicidae!

Ants always seem to be present around water. And we all know how fish seem to love ants! As a result, even the occasional ant that finds itself drifting on the water’s surface rarely goes unnoticed by the trout.

Like other social insects, most ants are sterile workers. But once a year the colony produces winged males and females to insure that the species stays healthy and widespread. Swarms of the winged adults fly from the nest in all directions looking for new nest sites. These swarms of fly ants often end up over, and in, streams and lakes. Such are the moments anglers live for. Most fly fishers have a story or two about an ant fall they experienced, and the wild fishing that ensued. I remember three days of fishing on a coastal lake when large fat trout were so easy to catch I began to think I was the greatest fly fisherman since Halford. Then the ants disappeared and I was quickly reminded of my more limited ability.

Because of the vast number of ant species, mating swarms often occur several times during the spring and summer. Your mission, should you decide to accept it, is to make note of when the swarms occur in your area. Then make sure you are not working on those magical days when the ants are falling!

Beetles

Beetles (Order – Coleoptera) top the scale when it comes to diversity. Over one third of all living animals on the planet are beetles. The true number of beetle species is anybody’s guess (300,000; 400,000; 500,000?), but there is no disagreement over their overwhelming diversity. Beetles range in size from the smallest of known insects – flea beetles reach a whopping one millimeter in length – to some of the largest of know insects – Dynastes tityus, or rhinoceros beetle, is as large or larger than a shrew.

With such diversity it should be no surprise that beetles have adapted to every conceivable habitat and life style. Fly tiers often find disaster from the work of dermestid beetles (better known as carpet beetles), which seem to enjoy eating only the best dry fly hackle necks they can find! On a happier note beetles occur in all variety of habitats located along streams and lakes. Some are full time residents of the water itself, but most live along the banks among rocks, sand and plant debris, or in the vegetation overhanging the water. Click beetles (family: Elateridae) seem to be frequent travelers over, and often in, the water. This is a diverse family of beetles (only about 900 species in the US!) that have the entertaining distinction of flipping themselves several inches into the air when laid upside down on a hard flat surface. This unique method of turning right-side up produces an audible “click” for which they are named. June bugs and Japanese beetles can also be very common along, and in, Midwestern and eastern streams.

Since any number of different types of beetles can end up on a trout’s dinner plate, it is usually not critical to match a specific size, color or shape of beetle. Exceptions occur, however. Occasionally a single species will be exceedingly abundant, in which case a more exact pattern will be important to your success.

Beetle adults float very low in the water (they often seem more submerged than floating), and thus can be very difficult to see on the water. I try to keep beetles in mind whenever I notice a strong breeze blowing through riparian trees. Even when beetles aren’t common on the water, it seems trout are happy to take one, whether it’s a natural or your imitation, whenever they have a chance. It you are looking for a good general summertime searching pattern, beetles would be a good first choice.

Grasshoppers

Grasshoppers (Order – Orthoptera) round out the big three terrestrials. While not as common as ants, or as diverse as beetles, grasshoppers have two essential qualities that make them great trout food – size and action. Most grasshoppers are a big meal for a fish. And like other big meals, salmonflies and green drakes for example, such meaty morsels bring the largest fish to the table. Add the enticing kicking action of a grasshopper trying to get back to shore, and you have an irresistible combination.

Grasshopper populations often fluctuate from year to year depending on prevailing weather patterns and food supply. Warm, dry weather during the spring results in better egg survival and faster growth of young hoppers than cool, wet weather. Populations also tend to be cyclic, with several banner years followed by several sparse years.

When hoppers are abundant fish routinely gorge themselves. At such times a hopper pattern will often produce well all day long. However, peak hopper activity will usually occur around mid-day. It also helps to have a breeze blowing so more hoppers end up off course and in the water. Such “hopper winds” can create incredible fishing for the largest trout in the stream or lake. For the best results hopper patterns should be fished within a few inches of the bank. The difference between good luck and bad luck when you are hopper fishing may be nothing more than getting your fly six inches closer to the bank.

There are many other terrestrials, besides the big three mentioned above, that become frequent items on the trout’s summer menu. Jassids (also called planthoppers), caterpillars or inch worms, moths, spiders, bees and wasps, all become food for trout during those warm, lazy summer days, when the exciting mayfly and stonefly hatches of spring are long gone.

To get an idea of just what terrestrials commonly fall into the trout’s window on your streams or lakes, you can make a simple surface water insect collector. You’ll need a plastic tray about 18 inches long and wide and about two inches deep. Attach some foam strips around the outside of the tray so it will float easily on the water. Now you’re ready to attach the tray with some string to a log, branch or a stake, so the tray is floating several feet out from the shore. Fill the tray half full of water mixed with a little dish soap, and your surface insect trap is ready. Any insects that land in the tray will quickly sink as the soap eliminates any surface tension. After a day or two check your trap to see what has been collected. You’ll see if ants, spiders or beetles are the dominant insects landing on the surface of your favorite trout stream. You’ll also be able to see their size and color so you’ll know just what kind of fly will best imitate them. You might be quite surprised at what turns up as the dominant surface food.

Experiment by putting your surface trap in different places on the stream. You will likely get quite different results if it is placed under a canopy of trees versus near a grassy bank. With this information you’ll see how the terrestrials fish feed on change in different parts of the stream as the vegetation along its banks change. Hoppers may dominate where grassy banks occur. Under a canopy of conifers beetles may be most common. Where deciduous trees, like alder or maple overhang the water, ants may be most abundant. Of course many other insects will turn up as well, even the adults of different aquatic insects.

A word of caution: Don’t get carried away with your collecting and take too many samples. While collecting a few dozen insects will never put a dent in the number of insects flying around on a summer afternoon, humans often overdo a good thing. We only visit a stream or lake, while trout and all they eat make it their home. Also check the regulations in your state. Some require permits for any type of stream collecting including insects.

The next time you hear that “hum” of insects in the air on a warm summer afternoon, remember that it is more than music to a fly fisher’s ears, it is also a key link in the annual diet of a healthy trout population.