Building a reputation — Caddisflies known for construction abilities, usefulness to fishermen in attracting trout

As virtually all fly fishermen and fisherwomen know, caddisflies are insects that build small cases of various materials, like pebbles, sand, leaves or twigs, found in various freshwater habitats.

Perhaps the greatest reason for anglers’ interest is that caddisfly larvae, pupae and adults are a favorite food for trout, and thus make great bait.

Caddisflies belong to the order Trichoptera. The name comes from the Greek words trichos (referring to “hairs”) and pteron ( meaning “wing”). Not surprisingly, Trichopteran adults have special hairs and scales on their wings. The common name caddisfly probably comes from Middle Ages England when cloth salesmen, called “cadismen,” attached elongated strips of cloth to their garments as an advertisement of their wares. Many pond and lake species of caddisflies attach elongated stems, grasses and twigs to their special cases. These fuzzy-looking cases then serve as protection or camouflage for the larva.

Caddisflies are closely related to moths and with their wings folded tentlike over their abdomen, they are often mistaken for small moths. Besides this look-a-like resemblance to their close relatives, caddisflies can also produce silk from special silk glands in the larval head. Larvae use this silk to bind various materials into protective cases that surround their somewhat unprotected abdomen. As the larva grows in size, the case is enlarged to fit its bigger waist size.

Some cases serve as effective camouflage, protecting them from visual predators like birds or fish. In other situations, the case seems to give them buoyancy and keeps them entangled in floating or standing masses of plant stems. In faster-moving water, the case may act as an anchor or ballast, keeping the case builder from being washed downstream.

These cases can take on a large number of shapes and sizes and are as varied as the materials caddisflies find in the habitat. The most common caddisfly in the Kenai River is brachycentrus, and its distinctive case looks like an elongated box with squared-off corners. They cut tiny, uniform sections of grasses and leaf fragments and assemble them like a miniature, hollow log cabin. There are other groups in the Kenai River that make distinctive cases of uniform sand grains in an elongated tubular shape reminiscent of a hot dog.

Not all caddisfly larvae make cases. Some use their ability to spin silk to create ultrafine nets between gravel or twigs that filter out fine particles drifting in the water column. The plant and animal materials that are captured by these tiny homemade nets are then consumed by the larva. Sometimes they will consume the whole net and particles together and then re-spin a new capture net.

Once the larvae have grown to a sufficient size and receive the appropriate temperature and light cues from the environment, they form a pupal case. This case is attached to a rock or nearby structure. A few days later they crawl out of their pupal skin and emerge as an aerial insect.

In midsummer along the Kenai River we often see large numbers of small gray caddisflies (brachycentrus) flying upstream to mate and lay eggs somewhere along the river.

Depending on the species, and there is a great deal of variety here, most of the caddisfly life cycle is spent as an aquatic larva with only a week or so as an aerial adult. However, there are some caddisfly species from the Kenai River that overwinter as adults.

Fishermen and women have a great many fly patterns that are tied to mimic the adult caddisfly on the surface of the water, laying eggs in a jerky, erratic pattern. There are an equal number of flies tied to mimic the larval stage and even some designed to mimic the vulnerable emerging pupal stage. These fly patterns work all over Alaska, since there are caddisflies in almost every freshwater habitat.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.

Water works: Insects master submerged breathing

I remember as an elementary school student watching a classmate attempt to drown a grasshopper by holding its head under water. The grasshopper endured the insult long enough for the childish attention span to turn to some other endeavor, and the insect was released to swim another day.

While the grasshopper was in danger of being squeezed too hard and perhaps getting a bath it neither needed nor wanted, it was in absolutely no danger of drowning with its head under the water.

Insects take in their air by way of a special set of spiracles on the thorax and the abdominal segments. The many spiracular openings lead to a series of very fine, hollow tracheal tubules that repeatedly branch until they are about one micron in diameter (one micron equals 1/1,000,000 of a meter).

These very fine tubules are surrounded by insect hemolymph (insect blood) that can absorb oxygen from the tubules and give back carbon dioxide. In order to refresh the air in these tubules, insects simply stretch or move the abdominal segments. If you watch an insect for a while, it will periodically stretch the abdomen, much like you and I do when we elevate the chest and draw in a fresh breath of air.

So how do the many aquatic insects live completely under water if they use air-filled tracheal tubes for oxygen exchange? There are several interesting solutions to this problem. Many aquatic insects are so small that they are able to simply exchange gases from the water right through their thin exoskeleton.

Another approach can be found in several groups like the mayflies and caddisflies that have special gills as larvae. Some of these gills look like a miniature brush of fine tubes, while others resemble flattened footballs attached to each abdominal segment. These gills exchange gases that are then channeled into the tracheal tubes.

Mosquito larvae and some other dipteran (flies) larvae have a tiny tube that they extend above the water surface so they can take air directly into their tracheal tubes. This is like breathing through a straw while still completely submerged.

(While we now appreciate the damage that was done to our wetlands, this is why years ago oil was spread over swamps in attempts to control mosquitoes. The surface oil would plug up the mosquito respiratory structures and the larvae would die.)

The colder the water is, the more oxygen it can hold. Warm water, on the other hand, can hold much smaller amounts of oxygen. Most streams in Alaska are so cold that it is no hardship for insects to get all the oxygen they need. During the winter months, when the water is at its coldest, the insects are able to get all the oxygen they can use so they are very active feeding and growing.

In warmer waters the oxygen is limited so insects must resort to additional measures. Some insects use hemoglobin in their hemolymph that is the same bright red color as our blood. The insect hemoglobin, just like ours, helps hold onto oxygen and spread it throughout the insect body. In an effort to extract the limited oxygen from warm water, some insects flap their gills in the current to bring them in contact with more water. Yet others can undulate their bodies to create a current or even build little tubes that funnel water past their gills.

When these immature aquatic insects leave the water to become aerial adults, part of the emergence process involves shedding their gills. They then use the normal spiracular openings and tracheal systems for their breathing as adults. When we consider that many insects can fly nonstop for hours, the insect’s simple breathing system apparently works quite efficiently.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.

Mosquitoes not gone for long

While we may have complained about an early cold snap this year, we certainly did not complain when the mosquitoes disappeared. But where are they now? Did the frost kill them all? And how do they reappear with the first couple warm days in the spring?

There are several dozen species of mosquitoes found in Alaska, and each of them has its own particular life cycle, although all of them are aquatic. Some prefer lakes, others ponds or various marshy habitats. Eggs are laid in the water and hatch out to become “wrigglers,” or larvae. Most of the larvae feed on algae or dead plant materials. They then form a pupa and shortly afterward emerge and become the aerial mosquitoes we love to hate.

The females usually mate and then look for a blood meal — and your arm looks like a great source of that blood. Note that only the females need a blood meal, so those buzzing around your head are all female mosquitoes.

When you and I swat at the mosquito that’s buzzing about, we probably don’t take the time to differentiate the particular species. But each species has its own approach to surviving the Alaska winters.

Many species overwinter as an egg that is laid in water during late summer or early fall. The egg remains underwater in a diapause state of inactivity until spring thaws. In the spring when water temperatures rise, the eggs hatch and the larvae feed voraciously. Within a week or so, they pupate and quickly become the aerial insects we know so well.

Another overwintering approach is for adults to find a safe hiding spot and wait out the cold of winter. Often these hiding spots are within leaf piles on the forest floor, in tree holes or under tree stumps. These areas, especially with a snow cover, provide insulation from the very coldest temperatures of winter.

An important goal for overwintering adults is to prevent ice crystal formation within their hemolymph (insect blood). First they reduce the amount of water in their hemolymph, kind of like concentrating their blood. Then they produce glycerol within the hemolymph, which acts as antifreeze. Now the adult is protected down to some pretty impressive temperatures. This activity is just like what we do to our automobile radiators each winter. However, if the temperatures around the adult fall below their protected temperature range, the adult will die. Very cold temperatures during a winter with minimal snow cover can reduce the spring population of early mosquitoes.

For overwintering adults, when the ambient temperatures rise in the spring, they are quickly able to leave the hiding place and seek out a blood meal. One particularly large Alaska mosquito uses this overwintering technique so well that it is called the “snow mosquito.” These are usually the first large mosquitoes we see flying around when there is still snow on the ground in early April.

While people are enjoying wintertime activities like skiing, snowmachining or ice fishing, beneath the snow and ice are mosquito adults or eggs, waiting for the return of warmer temperatures.


David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.

Science of the seasons: Shedding moonlight on daylight saving time

As we leave daylight saving time behind and set our clocks back an hour Sunday, I don’t want to start a discussion on its merits or lack thereof.

I’d rather talk about why we have time zones in the first place. Historically, each location on Earth had its own time, still called local time. It is defined by the sun reaching its highest point in the sky — which it does so exactly in the south. That’s called local noon. Local noon doesn’t depend on latitudes but on longitude only, hence we find time zones spread across a world map horizontally.

Local noon makes sense as it describes time conveniently at each longitude. A keen observer can be replaced by a good time piece.

The disadvantage came — big time — with the change in communication and especially transportation needs of the 19th century: train schedules didn’t just include the travel times, but they needed to accommodate the change in time depending on each destination’s longitude. The solution to that was to set up time zones, with New Zealand being the first country to do so in 1868, the United States and Canada in 1883 (by law in 1918). In 1884, 25 nations (12 American, 11 European, as well as Liberia and Japan) met for the Meridian Conference in Washington, D.C., and established Greenwich as the Prime Meridian and created 24 time zones of 15 degrees longitude each.

There are exceptions to the latter, especially concerning national and state borders. Usually these exceptions are subtle: Ogallala, Neb., is on Mountain Time while Plateau, Texas, is on Central, even though it’s two degrees farther west. Some exceptions are more extreme: all of China is on one time zone, although the country spans 60 degrees (and therefore should technically be divided into four time zones). Lublin in Poland and Santiago de Compostela in Spain are in the same time zone, even though they are 30 degrees apart. In contrast, Russia is in accordance with the meaning of the Meridian Conference, spanning 10 time zones over 160 degrees.

Alaska is on one time zone (with the exception of the Aleutians West of Umnak Island), although Ketchikan and Nome are 35 degrees apart. What that means is Southeast Alaska’s local noon occurs near 12 noon, central Alaska’s local noon is around 1 p.m. and Western Alaska’s local noon around 2 p.m. Sunrise and sunset are equally shifted, with Yakutat having both its sunrise and sunset 1.5 hours earlier than Bethel throughout the year.

Harvest moon

The harvest moon is the full moon closest to the autumnal equinox, and therefore occurs within two weeks before or after Sept. 22. At that time of the year the moon is in the constellations of Pisces and Aries, which stay close to the horizon when they rise in the east; hence the moon stays close to the horizon, as well.

That gives rise to a couple of phenomena. One is based on the physics of diffraction: close to the horizon, moonlight (which is reflected sunlight) has to travel through more of Earth’s atmosphere. Air, which is mostly nitrogen and oxygen molecules, scatters more of the blue part of the spectrum, leaving the moon more reddish.

The other is completely psychological: what is called the moon illusion makes the moon appear larger closer to the horizon than up in the sky (although either are of the same angular size). Even though there is no single hypothesis explaining the effect and different people may experience it differently, one such hypothesis holds that to us the moon looks farther away on the horizon than somewhere in the sky (where it is surrounded by sky) – because it is still of the same angular size. By appearing farther away, it also appears to be bigger. In other words, this is not what the moon really looks like, but it’s based on how our brains interpret what our eyes see. Good comparisons are optical illusions that fool all of us (like the same size dots where one appears larger than the other, the parallel lines that appear nonparallel, etc.).

Also, while the moon’s orbit around Earth is a nice ellipse, describing its motion and appearance relative to the horizon becomes quite complicated, because two different spherical coordinate systems are merged. One consequence is that while, on average, the moon rises 50 minutes later each night, during the fall it rises only 30 minutes later each night. Therefore twilight turns quickly into a brightly lit evening, assisting farmers to get their crops in.

Andy Veh is a physics and astronomy professor at Kenai Peninsula College’s Kenai River Campus. E-mail your science questions to redoubtreporter @alaska.net.