Contents

An Entomologist's Encounter with a Fly Fisher from the Missouri Ozarks

Collecting and Preserving Aquatic Insects

A Fly Fishers Anatomy of an Insect

Identification Key to Common Aquatic Insects of Colorado

• Metamorphosis and Life Cycles
• Mother's Day Caddisfly Hatch on the Arkansas River
• Caddisflies (Trichoptera)
• Mayflies (Ephemeroptera)
• Stoneflies (Plecoptera)
• Dragonflies and Damselflies (Odonata)
• Dobsonflies and Alderflies (Megaloptera)
• Beetles (Coleoptera)
• True Flies (Diptera)
• True Bugs (Heteroptera)

Checklist of Aquatic Insects in the WDTU Teaching Collection

Selected Bibliography of Aquatic Insect Literature for the Fly Fisher

Aquatic Insects and the Internet

While pursuing a doctoral degree at the University of North Texas (1989–94), I conducted research on the caddisfly fauna of the Ozark and Ouachita Mountains in Arkansas, Missouri, Oklahoma, and southwestern Illinois. During my first year of intensive field collecting, the late Bob McCalmont of Lebonon, Missouri contacted me.

Bob was an avid fly fisher at the Bennett Spring State Park trout fishery. He was also an entomological enthusiast!…interested in knowing as much as possible about the aquatic insects of Bennett Spring. For many years, Bob collected and preserved larval and adult caddisflies, much in the same manner that professional entomologists do. His efforts to identify what he collected were aided by a microscope he had set up next to his fly tying vise. Bob’s initial contact with me occurred after he found out I had a scientific collector’s permit to sample in Missouri state parks. Bob wanted to know if I had some time to look over his caddisfly identifications and let him know how he had been doing. I was more than happy to oblige since I saw this as an opportunity to see some caddisfly material from an area of the Ozarks that I had not yet sampled. To my pleasant surprise, many of his family- and genus-level identifications were accurate, and I was able to identify all of them to species. However, there was one species that caught my attention as being quite unusual. It was a species in the long-horned caddisfly (family Leptoceridae) genus Ceraclea. I compared it to the known species of the genus in North America and soon realized that Bob's specimens represented a species new to science.

The next step was obvious. The caddisfly without a name had to be described and illustrated in great detail. I described the male, female, pupa, and larva from the specimens that Bob collected and from additional specimens I collected on a subsequent visit to him in July, 1991. The final step involved giving this new species a name. I felt honored to name it after Bob, calling it Ceraclea maccalmonti. The description of this species was published in 1992 in the Proceedings of the Entomological Society of Washington.

I was fortunate to share some time with Bob collecting aquatic insects at Bennett Spring before his death from cancer in 1993. He and his wife, Ruth, were some of the nicest folks I had ever met while in the field.

I often tell this story to fly fishers I meet, because I know many of you spend a great deal of time on the water not just fishing, but also flipping rocks to see what the insect menu of the day reveals. You never know what you’re going to find. Despite some attempts by scientists to inventory the aquatic insect fauna of the western United States, we still do not have a good understanding of species assemblages and their distribution.

Collecting and studying aquatic invertebrates (e.g., insects and crustaceans) can be a rewarding and valuable dimension of any fly fishing experience. Several fly-fishing vendors sell basic collecting kits, but many items can be purchased inexpensively at your local department or hardware store.

Virtually any kind of fine mesh (0.5 to 1.0 mm) dip net or collecting screen can be used to collect nymphs and larvae of aquatic insects. Homemade collection screens can be constructed from two strips of molding and nylon window screen. A rectangular piece of window screen is stapled to the molding with a staple gun. No matter how big the screen is, it can be stored in scroll fashion in a large rear vest pocket. Aquarium nets are also convenient for this reason. Capturing stream invertebrates is best accomplished by positioning the collection device on the stream bottom, downstream of the area you want to collect. The substrate upstream of the device is then disturbed so organisms are carried into the collection mesh. Dipping along lake or pond margins is an effective way to collect invertebrates in still water. After a collection has been made, you can remove organisms with a small pair of forceps or tweezers. Care should be taken not to damage delicate organisms such as mayfly nymphs.

Aquatic invertebrates should be preserved in 70 to 80 percent alcohol. I recommend using 80 percent since the organisms you add to it will carry some water and dilute the alcohol. If the alcohol becomes too diluted, your specimens will become mushy and useless for study. Ethyl alcohol should be used whenever possible because it provides the best fixation of body tissues and is good for long term storage. However, isopropyl alcohol is a good substitute and can be purchased cheaply in drug stores. Whichever preservative is used, you should change it once with in a day or two after collecting.

Collections from different localities and dates should be preserved in separate containers and individually labeled. Small glass vials with tight-fitting screw cap lids or rubber stoppers make the best storage vessels. Labeling is very important to professional entomologists because is provides valuable information on the distribution and seasonality of organisms. The minimum amount of collection information should include state, county, name of water body, location of water body (e.g. road route, mileage to nearest town), elevation (if available), date (day, month, year) and name(s) of collector(s). Label information should be written on 100 percent bond paper using a pencil or alcohol-proof black ink. Labels should be placed inside the vial with the organisms. Below is an example of a typical label that I use in my fieldwork:

Identifying and studying your collections can be rewarding for several reasons. First, you can learn more about the different kinds of potential trout food organisms present in a stream you fish. Second, the size, structure, and color of preserved organisms can provide tips on how to model artificial flies. Since many fly fishers are also conservationists, knowledge of the diversity of aquatic insects and other invertebrates can provide information on the general "health" of particular aquatic habitats. Basic identifications (order and family-level) can be made with a hand held magnifying glass. For more refined identifications (genus and species-level) it is necessary to use some type of dissecting microscope. The reference listed above by McCafferty (1981) is an excellent resource for additional information on collecting, preserving and identifying aquatic invertebrates.

It is unnecessary to be versed in the entomological language of an insect's anatomy. However, some terms should be understood because they are useful in identifying major groups of insects and in tying flies to imitate various naturals. An insect is made up of three main body regions: (1) a head, (2), a thorax, and (3) an abdomen. The head contains the eyes, a pair of antennae, and the mouthparts. The middle thorax region consists of the wing pads (some larvae) or wings (adults) and the three pairs of legs (except true fly larvae). The abdominal region is tubular and in some larvae or adults there may be two or three "tails" or cerci. In larvae there are usually various types of gills attached and some species may even have one or more pairs of clawed, leg-like structures called prolegs. In adults, the abdomen it is where the reproductive system is located. Class dismissed!

The following key is intended to provide fly fishers with a basic guide to identify common groups or orders of aquatic insects found in Colorado streams and lakes. This key, because of special variation form the characters used below, will not accurately identify some insects. For further information and lower levels of identification (such as family, genus or species), please consult the bibliography below for references to more specialized identification guides.

1. Beginning at Key No. 1, read the description of characters for parts A and B.
2. Decide which part (A or B) best fits the insect you are looking at.
3. Follow the row to the right column where you will find a name or a number. A name indicates that you have identified the insect. A number leads you to the next key number where you will evaluate another pair of descriptive characters.
4. Click on the number and repeat this process until you have identified the insect.
5. Click on the name to go directly to the overview of that group.

*Adapted from Ward and Kondratieff (1992).

Various insect orders are grouped by the type of metamorphosis they exhibit. Metamorphosis refers to the change in size and form of an insect as it moves through a succession of life stages (egg, larva, pupa, and adult) during a single generation or "life cycle". After hatching from the egg, a larva (=nymph) undergoes a variable number of molts to increase in size. Molting is the process where the old exoskeleton is shed and a new one is formed. Entomologists refer to the shed exoskeleton as the "exuvium", while fishermen apply the term "shuck". Shucks of stoneflies and other aquatic insects can often be seen attached to emergent objects in a stream or lake. Newly molted insects are often white or cream-colored in appearance. As the new exoskeleton forms, pigments in the insect cuticle begin to appear. When the larva reaches maturity, it develops into the next life stage, which may or may not represent the end of its life cycle. The form of an insect between molts is termed an "instar". The number of instars exhibited is dependent on the type metamorphosis. Three types of metamorphosis are recognized in insects: 1) ametabolous, 2) hemimetabolous, and 3) holometabolous. Familiarity with the life stages and metamorphosis of major aquatic insect groups can enhance the basic understanding of life cycles and presentation of artificial flies throughout the year.

Ametabolous metamorphosis refers to insects that undergo no change in form after hatching from the egg. In other words, the nymph looks exactly like the adult except for a difference in body size. Even after reaching sexual maturity, the adults continue to molt. The only order to have aquatic representatives exhibiting this type is the Collembola, or springtails. These minute insects (1 – 3 mm) are wingless and spend their lives jumping around on the surface film of water and other objects close to shore.

Hemimetabolous metamorphosis refers to an incomplete change in form. Insects exhibiting this type of metamorphosis pass through an egg, nymph, and adult life stage. Wings begin to develop as external pads on the thorax of nymphs (see photo of stonefly nymph). Depending on the species, nymphs may molt as many as 15 to 40 times. Terrestrial representatives exhibiting this type include the orders Orthoptera (crickets, grasshoppers) and Hemiptera (true bugs). In these orders, the nymph resembles the adult but lacks functional wings and does not reproduce. Nymphs also share the same general terrestrial habitat and food resources as the adults. Aquatic representatives exhibiting hemimetabolous metamorphosis include the Plecoptera (stoneflies), the Ephemeroptera (mayflies), and the Odonata (dragonflies/damselflies). The nymphs of these orders are adapted to an aquatic lifestyle unlike the adults, which are terrestrial. Mayflies are unique among the hemimetabolous insects in having two winged life stages. The first is called the subimago, or "dun" by fishermen, and has smoky-colored wings. After emerging form the water, the subimago will fly a short distance to rest on an object where it molts once more to a reproductive adult (=imago) stage, or "spinner", as referred to by fishermen.

Holometabolous metamorphosis refers to a complete change in the form of an insect. In this type, individuals pass though four life stages (egg, larva, pupa, and adult). Larvae molt from three to six times. Wings begin developing internally from discs in mature larvae and are not apparent until the pupal stage. The pupa represents a transitional stage between the radically different larva and adult (see photo of adult and larval caddisfly). Pupae do not feed and are generally less active than larvae or adults. Orders exhibiting this type of metamorphosis includes the Trichoptera (caddisflies), Megaloptera (hellgrammites, fishflies), Diptera (true flies, midges), and Coleoptera (beetles).

On two fishing trips during April and May 1997, I had the pleasure of fishing the segment of the Arkansas River between Parkdale and Salida. Both trips had two primary objectives; to catch some trout, and witness the famed caddisfly blizzard that takes place each year about that time. Being a caddisfly researcher, I was slightly biased towards the latter purpose of the trips.

The caddisfly responsible for this springtime hatch excitement is named Brachycentrus occidentalis, whose identity was first described by Nathan Banks in 1911. This species belong to the trichopteran family Brachycentridae. It is known by many local names, but the most common are "grannom" and "Mother’s Day caddis." The distribution of B. occidentalis is widespread throughout western North America. A related species, B. americanus also described by Banks but in 1899, has a similar distribution; however its peak emergence usually occurs much later in the summer. Anglers should be aware that specific emergence periods would vary among geographic regions and elevations. Both Brachycentrus species occur in enormous populations in Colorado streams and rivers. Their shear biological productivity and synchronous emergence makes them a primary food resource for fish and an entomological wonder for flyfishers.

Mature larvae are approximately 10 mm in length (size 14 - 16 hook). They construct a four-sided case of rectangular strips of bark and leaves. The narrow case tapers from front to back. Larvae use silk to fasten the strips together and to anchor the leading edge of the case to some stable substrate in the water, usually a large rock or submerged tree branch. The front opening of the case is always pointed into the current. Larvae assume a "filtering pose" by extending their middle and hind legs outward. Each of these legs has a fringe of hairs that filter out food items carried in the current. Larvae also graze on algae growing on the substrates to which they are attached. In the Arkansas River segment that I visited, it was not uncommon to find large rocks each having upwards of 100 to 200 larvae.

From the time eggs are laid and hatching occurs, larvae require one year to mature. Upon maturation, larvae often aggregate in large numbers sometimes stacked three or four deep. They seal off the front of the case with a thin silk closure and then undergo extensive physiological changes to reorganize body tissues forming wings, reproductive organs, and other features typical of the adult stage. This transitional period is termed the pupa. Superficially it resembles the adult but has some unique structural features such as abdominal hook plates and scissor-like mandibles. Early in its development, the pupa is cream to greenish colored. Prior to emergence the mature pupa has dark eyes, dark wing pads, and more pronounced body colors typical of the adult. Anglers can quickly determine when emergence is likely to take place by opening a few pupal cases to observe these features.

Emerging pupae use their mandibles to cut open the cases. They wriggle their way out and swim to the surface while being carried downstream by the current. Emergence of B. occidentalis is highly synchronous, with the peak lasting for about two to three weeks. My observations on the Arkansas River indicate that emergence takes place during the late morning and early afternoon hours. On calm days, clouds of adults can be seen flying upstream to mate. On windy days, adults take refuge in riparian bushes and trees. Although never documented positively, adults probably only live for a few days, just long enough to reproduce. Facing in opposite directions, mating pairs are connected by the tips of their abdomens. After mating, females deposit gelatinous egg masses containing up to several hundred eggs. Entomologists refer to egg deposition as "ovipositing." Ovipositing females can be seen flying low to the water and occasionally hitting its surface. Once deposited, the sticky egg mass eventually attaches to the substrate and swells in size to that of a small gumdrop. On my trip to the Arkansas River on Mother’s Day, I observed many large rocks that were literally covered with swollen egg masses.

The owner of a local fly shop in Salida told me that anglers were having their best success using emerging pupal patterns (for example, LaFontaine's Deep Sparkle Pupa). I had been using a size 16 tan-brown elk hair caddis pattern with no "fish on" success. Although I had numerous hits, I guess my dry fly was no match to the hundreds of other live B. occidentalis fluttering in the same vicinity.

One of the most important insects known to flyfishers is the caddisfly. Caddisflies belong to the order Trichoptera and are closely related to butterflies and moths (order Lepidoptera). There are approximately 1700 species of caddisflies in North America with the World fauna variously estimated between 10 and 50 thousand species. 188 species have been documented from Colorado.

Caddisflies undergo complete metamorphosis, which includes an egg, larva, pupa, and adult. For most species, the larval and pupal stages inhabit a wide range of freshwater habitats from spring seeps to large rivers and lakes. In some species, these stages are exclusively terrestrial. One Australian species inhabits marine barrier reefs and deposits its eggs in the digestive system of starfish! Caddisfly lifecycles can vary from a few months to a couple of years with the adult stage being the most short-lived. Some groups (e.g. Brachycentrus spp. or grannoms) are highly synchronous in their development and ultimately emerge in large swarms for a one or two week period. Other species have asynchronous development and multiple generations throughout the year such that adults are found almost year round.

Caddisflies range in size from approximately 2mm (No. 24 or 26 size hook) to over 40 mm (No. 4 or 6 size hook). Larvae are soft-bodied and usually cream-colored or greenish with the head and thorax (segment of body possessing the legs) variously colored from tan to dark brown or black. Some larvae like the Rhyacophilidae (sedges) are free-living predators. Other larvae construct fixed or portable cases of mineral and organic materials (e.g., twigs, bits of leaves, wood, or algae). These cases are often quite intricate in design and usually important in the identification of a particular group. The pupal stage is often misunderstood as an inactive part of the life cycle. To the contrary, much physiological activity is taking place during this period (e.g. development of wings and reproductive system) to prepare the caddisfly for its adult life. Pupation takes place inside a cocoon. Prior to emergence, the pupa uses its scissor-like mandibles to cut and wriggle its way out of the cocoon. Once free of the cocoon, the pupa will either swim to the surface of the water or crawl out onto some emergent substrate like a log or rock. The pupa will take a few seconds or minutes to free itself of the pupal skin and fly off. It is during these emergence or "hatch" activities that caddisflies are most vulnerable to fish and other predators.

Unlike many ornately colored butterflies, caddisfly adults are rather drab in color. Wing and body colors range from white and tan to mottled shades of brown. Other characteristic features include long, whip-like antennae and hairy wings that are held in a "tent-fashion" over the body. Adults do not feed but some are able to imbibe liquids. Their primary functions as adults, are to disperse and reproduce. Mating individuals face in opposite directions and can usually be observed on streamside objects and bridges. Females deposit eggs in masses, strings, or singly on large rocks or woody debris. This is accomplished either by diving or crawling into the water and swimming or crawling to the bottom.

Like caddisflies and stoneflies, mayflies are an important group of aquatic insects to both trout and flyfishers. Mayflies belong to the order Ephemeroptera that literally means "short-lived wing". This name was derived from the fact that mayfly adults only live from a few hours to a few weeks. There are approximately 600 species known in North America with 97 of them being documented from Colorado. Mayflies undergo incomplete metamorphosis; their life cycle includes an egg, nymph, and adult stage.

The adults are easily identified in the field by their triangular-shaped wings, which are held vertically, unfolded above their body and the presence of two or three long, slender tails. Their wings (two to four in number) represent a very primitive condition in insects because they lack the wing folding mechanism found in other groups like caddisflies and stoneflies. This primitive condition is also found in dragonflies and damselflies (order Odonata). Mayflies range in size from a few millimeters to a few centimeters. Body coloration ranges from white and yellow to various shades of red, brown, olive, and black.

As mentioned previously, adults live for only a very brief period, just long enough to disperse and reproduce. Males are usually differentiated from females by their enlarge compound eyes. This modification allows males to quickly spot and mate with females of the same species while flying. Swarms of males can usually be observed above streams and rivers in an "up and down" flight pattern. Females will fly directly through the swarm until males intercept them. Mated females whose abdomens are often distended with fertilized eggs, deposit their load on the water surface or submerge themselves and lay eggs underwater. Surface egg laying females often die on the water with their wings out stretched. This has been termed by flyfishers as the "spinner fall". Dry fly patterns imitating this can be very effective in catching rising trout. Upon egg hatching, tiny nymphs disperse and take up residency in a wide range of aquatic microhabitats. The basic morphology of a particular family can indicate certain adaptations for living in a variety of stream substrates and current. For example, the families Baetidae and Oligoneuriidae have a torpedo-shaped body and tails with dense hair fringes that function like paddles. These families are common inhabitants of swift riffles sections and their nymphs can be found feeding and darting about on exposed rock surfaces. Other riffle dwelling mayflies like the Heptageniidae, have flattened bodies and legs, and eyes situated on top of the head. This type of morphology indicates that they are "current avoiders". Some heptageniid mayflies like Rhithrogena have their abdominal gills modified ventrally to form a friction disk, which is used to help maintain their position on the substrate. Another major group of mayflies includes those that burrow into soft aquatic substrates like sand and mud. The most common group of burrowing mayflies are members of the family Ephemeridae (e.g., genus Hexagenia). Nymphs in this family are among the largest mayflies known. Their leg segments are scoop-like and modified for burrowing. The head possesses a pair of mandibular tusks.

Mayfly nymphs feed by actively gathering or filtering organic detritus (fragments of dead leaves, wood, aquatic plants). Nymphs will undergo molting as many as 30 to 40 times before they are ready to emerge. Mature, pre-emergent nymphs are readily distinguished by their enlarged, dark wing pads located on top of the thorax. Adult emergence, or "the hatch", occurs when the nymph crawls onto some emergent surface or swims to the surface and leaves the last nymphal skin or shuck. However, the winged individual produced is not yet a full-fledged adult. This preadult stage is termed the subimago; they typically have smoky-colored wings and need to molt one more time before becoming a true adult capable of reproducing. Adults generally have clear wings and do not feed.

Stoneflies are a small, primitive group of insects belonging to the order Plecoptera. The name Plecoptera literally means, "pleated-wing", referring to the fold present in each hind wing while the adult is at rest. Like caddisflies and mayflies, stoneflies are extremely important to fly fishers. They often constitute a very significant portion of the available food resources to trout and other insectivorous fishes. There are 608 species of stoneflies in North America. Approximately 100 of these species occur in Colorado. One of the most talked about stonefly species in the western United States is the salmonfly, Pteronarcys californica. This species is very common in Colorado and usually receives a great deal of attention by fly fishers prior to its summer emergence, which sparks a feeding frenzy among trout.

A typical stonefly life cycle includes an egg, nymph, and adult. This cycle is said to be "incomplete" since it does not possess a pupal stage as seen in the caddisflies. Stoneflies range in size from a few millimeters (family Capniidae) to over 5 centimeters (family Pteronarcyidae). They’re body coloration ranges from black and various shades of brown to golden-yellow and light green. Some stoneflies like Acroneuria and Claassenia sabulosa have very ornate color patterns on their head, thorax, and abdomen. Stonefly nymphs and adults are easily distinguished from other insect groups by the presence of a pair of long cerci (=tails) at the end of the abdomen; the antennae are very long (much longer than the head) and robust, sometimes resembling cerci.

Stonefly nymphs are restricted to flowing, highly oxygenated aquatic habitats. This includes springs, streams and large rivers. However one species, Utacapnia tahoensis, is wingless and occurs in deep sections of Lake Tahoe, Nevada. The nymphs are intolerant to poor water quality. For this reason they, along with most mayflies and caddisflies, are important to aquatic biologists as water quality indicator organisms. Nymphs feed on a variety of food materials including detritus, algae, and other aquatic insects. They may spend anywhere from a few months to two or three years in the water before they emerge as adults. Prior to emergence, nymphs crawl to the stream bank or some emergent object like a rock, log, or bridge piling. At these sites the nymphal skin is shed. For the most part, adults resemble the nymphs except for the presence of wings. Some species do not possess wings as adults or have greatly reduced wings. In most species though, the wings cover most of the abdomen.

Adult stoneflies have evolved a very complex form of vibrational communication for the purpose of mate location. This form of communication, or "drumming", as it is referred to among stonefly researchers, is species specific. Male stoneflies send initial drumming signals by tapping or rubbing their abdomens on resonant substrate like a tree branch or leaf. Any reproductively receptive female of the same species will respond to the male signal with her own call. A male receives the female signal using sensory structures located on his legs. The male synthesizes this information to locate the female and then mate with her. While explained in a very simplistic manner here, this form of communicational behavior is extremely complex and takes on many variations.

Two excellent books are available to fly fishers that summarize the identification, biology, and ecology of this fascinating group of aquatic insects. They are: Nymphs of North American Stonefly Genera (Plecoptera) by Stewart and Stark (1988) and Stoneflies for the Angler by Leiser and Boyle (1982).

Dragonflies and damselflies, or "odonates", belong to the insect order Odonata. The ordinal name is derived from the Greek "odon" meaning tooth, likely referring to the well-developed teeth of the nymphal mouthparts. These insects, along with mayflies, are the most primitive of the winged insects because the adults lack the wing-folding mechanism found in other advanced groups like the caddisflies and true-flies (e.g., midges). As a result, adult odonates hold their wings at 90-degree angles to the long axis of the body while at rest. Dragonflies hold their wings out to the sides, while damselflies hold their wings together, but straight up above the body. The wings are delicate and clear. Some species have blotches or bands of color in the wing membrane. Several folknames have been attributed to the adult stage including "mosquito hawk", "snake doctor", and "devil’s darning needle". There are approximately 650 species of dragonflies and damselflies known from North America, with about 60 of these being documented in Colorado. Fly fishers that frequent lakes or ponds during the summer months can have productive fishing trips for trout, bass, and panfish using a damselfly pattern.

Odonates have an incomplete life cycle which includes an egg, nymph (=larva), and adult. The nymphs inhabit a wide range of freshwater aquatic habitats including springs, lakes, and streams. Nymphs are easily distinguished from other aquatic insects by an extendible labium or "lower lip". Some nymphs have a flat labium while others have a spoon-shaped labium. The labium is equipped with spines and teeth that aid in feeding. When a prey item is spotted the labium is extended very quickly much like a frog’s tongue. Jaws at the tip of the labium hold the prey while the labium is withdrawn, bringing the food back to the mouth where it is eaten.

Dragonfly nymphs are large, robust insects with maximum lengths up to 60 - 70 mm. They have internal abdominal gills that perform a respiratory function when water is pulled in through the anus. In addition, water can be expelled rapidly to provide a burst of jet propulsion to help the nymph avoid possible predation. Damselfly nymphs are smaller, more slender insects compared to dragonfly nymphs, and have three blade-like, external gills at the tip of the abdomen.

Adult dragonflies and damselflies are extremely territorial and can often be observed "patrolling" shorelines of lakes and streams. They are also fierce predators and play an important role in controlling mosquitoes. Adults capture other smaller flying insects and eat while flying. This is facilitated largely through their well developed compound eyes and modified legs. The legs are equipped with spines and get progressively longer front to back, such that the middle and hind legs can scoop forward to hold and manipulate prey. The erratic flight of some individuals is often evidence of this feeding behavior. Sometimes, a male and female of the same species can be seen flying connected together in a ring fashion that is known as the "wheel position". It is a reproductive flight behavior enabling the sexes to copulate while flying. Following copulation, females deposit their fertilized eggs in the water by fluttering just above the water and dipping the tip of their abdomen in the water. Females of some species will even crawl down a submergent object to lay eggs.

Odonate nymphs are rather drab-colored in various shades of tan, brown, and green. Adults on the other hand, are more brilliantly colored, displaying various shades of green, red, blue, and purple. Like amateur butterfly collectors, many people collect and study adult odonates for this reason. In many cases, coloration patterns are secondary sexual characteristics that distinguish the sexes as well as species.

A group of aquatic insects that is often overlooked by flyfishers is the order Megaloptera. This order, which literally means "large wing" includes insects commonly, referred to as dobsonflies and alderflies. This order is distributed throughout North America with larvae living in a wide range of aquatic habitats from streams, rivers, and springs, to bogs, ponds, and lakes. Larvae of some species can even be found in the water that collects in pitcher plants. Only a few megalopteran species are known to occur in Colorado. The most common of these species, Corydalus cornutus, is restricted to large river systems at lower elevations on the eastern and western slopes of the Rocky Mountains.

Megalopterans undergo complete metamorphosis, which means they pass through a pupal stage in transforming to an adult. Their life cycles are longer that most other species of aquatic insects requiring from two to five years to complete. Larvae, often referred to as hellgrammites, are highly predacious and feed on a variety of aquatic insect larvae and other invertebrates. Depending on the species, the length of mature larvae ranges from 20 to 80 mm. Larvae are generally dark brown, although some may have some ornate pale markings on the head and thorax. The larval abdomen has numerous lateral finger-like processes that assist in respiration. Larvae also have well developed walking legs and two pairs of stout hooks located on prolegs located at the tip of the abdomen. These feature allow them to move about freely in swift flowing riffles where they are most often found living under large rocks.

Prior to pupation, larvae migrate to the margins of aquatic habitats where they burrow into moist sediment and create a pupal chamber. Adult megalopterans generally emerge during the summer months. During this time they are most active at night, especially on calm, warm evenings. Adults are among the largest of all insects, with some species having wingspans approaching 100 mm. The male of Corydalus cornutus is easily distinguished from the female by a pronounced sexual dimorphism where their mandibles are modified into enlarged, crossing tusks; the female’s mandibles are unmodified. Females lay their eggs on tree leaves overhanging water and on other objects such as bridges. Upon hatching from the eggs, young larvae fall into the water and begin their long aquatic existence.

There is virtually no need for flyfishers to tie flies imitating the megalopteran pupa or adult, mainly because fish are unlikely to see these life stages. However, imitations of the larval stage can be most useful in catching a variety of game fish species. One excellent imitation that comes to mind is a brown or black beadhead wooly bugger. This pattern should be tied on a number 6 to 10-sized hook and fished on the bottom of riffles and runs.

Beetles belong to the insect order Coleoptera and represent the most diverse group of insects in the world with well over 300,000 described species. Countless thousands of species remain to be described and formally named by entomologists. The name Coleoptera literally means, "sheath wings", referring to the hardened, armor-like forewings that cover most of the body. Beetles undergo complete metamorphosis meaning that their life cycle consists of egg, larval, pupal, and adult stages.

Unlike other insect orders that spend most of their life cycles either in an aquatic (e.g., caddisflies, mayflies) or terrestrial (e.g., grasshoppers) environment, beetles have successfully invaded both. Truly aquatic beetles can be found in almost any type of freshwater habitat. Some groups can be found in and along intertidal marine habitats. Other beetle groups are referred to as "semi-aquatic" meaning they are mostly associated with moist or wetted areas near aquatic habitats. Most aquatic beetles are either predators or scavengers. Some, depending on the life stage, will feed on detritus, living vascular plants or algae. Below, I review three families of aquatic beetles that fly fishers are likely to encounter.

The family Elmidae, or "riffle beetles", are very common in streams and rivers throughout the world. The larvae and adults are very small, measuring up to approximately 5 mm (18 - 22 hook). Their coloration is tan, brown, or black. Larvae are torpedo-shaped, while adults are oval-shaped. The legs of adults (see photo) are well developed with stout claws…an adaptation permitting them to move around in swift currents. Both life stages may be found in similar habitats such as under submerged rocks or in rock/wood crevices. Interestingly, riffle beetle pupae are terrestrial, living in moist ground or wood near the water. Following emergence, adults may fly for a short period before re-entering the aquatic environment.

Another common group of aquatic beetles is the family Dytiscidae, or "predacious diving beetles." As indicated by their common name, these beetles are extremely voracious predators as larvae or adults. Some larvae have been known to capture small minnows! Larvae and adults of this family span a much greater size range from 2 mm up to 50 mm. They tend to inhabit still waters such as ponds and lakes, although some can be found in similar stream habitats such as pools. Various types of diving beetles can be observed diving and swimming in shallow water where there is abundant aquatic vegetation. Some adults are attracted to lights at night.

One group of aquatic beetles that people are most familiar with is the family Gyrinidae, or "whirligig beetles." These beetles are extremely fascinating in that their bodies have evolved a form adapted for living on top of the water. Their compound eyes (see photo) are split in half for simultaneous up/down vision. Adults are often observed swimming on the surface of lakes and stream pools in a very erratic fashion. They can also be found in large aggregations or swarms of hundreds or thousands of individuals. These are all highly desirable traits for avoiding predation in a very precarious aquatic microhabitat. Whirligig beetles are black, ranging in size from a few millimeters up to 15 mm.

In previous Bug Net articles, I have featured certain aquatic insect groups that are important to fish as a food resource as well as to fly fishers in providing models for their fly patterns. In this article, I feature the true-flies, which belong to the order Diptera. This order is extremely diverse having approximately 25 to 30,000 described and undescribed species in North America. One example of this group that is familiar to all of us is the common housefly. The Diptera exhibit complete metamorphosis, which means they go through a pupal stage. Common names of various dipteran sub-groups having an aquatic larval stage include blackflies, horseflies, mosquitoes, craneflies, and midges. The term "midge" is often loosely applied to mean any small fly. Entomologists reserve the term midge when referring to certain families of Diptera such as the Chironomidae (or non-biting midges and bloodworms) or Ceratopogonidae (or biting midges, punkies, no-see-ums). The remainder of this article will focus on the common aquatic family Chironomidae.

Larval chironomids range in size from a few millimeters (No. 22 - 26 hook) to over 20 millimeters (No. 12 - 14 hook). Their tubular, maggot-like bodies are composed of a well developed, hardened (=sclerotized) head, a thorax possessing a single pair of unsegmented prolegs just behind the head, and an abdomen that terminates in a pair of unsegmented anal prolegs and a cluster of anal gills. Therefore, unlike other aquatic groups such as caddisfly, mayfly, and stonefly larvae, chironomid larvae do not have any jointed thoracic legs. Larval head colors, which are often visible to the naked eye, are usually golden, brown, or black. Larval body colors (in life) range from clear to shades of green and red. The name "bloodworm" refers to some of the largest larvae (e.g., genus Chironomus) that have bright red bodies and are very common in streams and lakes that are polluted or have some significant organic enrichment. They are especially common in the poorly oxygenated bottom water and sediments of lakes during the summer months. Their red coloration comes from the respiratory pigment hemoglobin, which is similar to the human hemoglobin but differs in its molecular composition and specific physiological function. When dissolved oxygen (DO) in the water and bottom sediments drops to the point that it becomes intolerable to most other aquatic organisms, chironomid hemoglobin facilitates these larvae to survive short periods of stressful DO levels.

Larvae feed on a variety of materials including detritus and other plant materials. Some are even predacious and feed on other invertebrates and midge larvae. Like caddisfly larvae, midge larvae also utilize a variety of substrate materials to construct retreats or tube cases. However their architectural efforts are not nearly as diverse and fascinating as those of caddisflies. Larval chironomids constitute a very significant portion of the food resources available to fish in aquatic ecosystems. Their population densities can reach or exceed tens of thousands of individuals in a square meter area.

Once larvae have matured, they go through a brief pupal stage and later emerge as winged adults. The adults are "mosquito-like" but do not feed. Unlike other common aquatic insect adults that have two pairs of wings, chironomid adults only have a single pair of clear wings. Males and females are easily distinguished in the field by the structure of their antennae. Males have very bushy or plumose antennae, while females have simple, hair-like antennae. After mating, females usually deposit underwater, a single egg mass that contains up to several hundred eggs. Eggs begin to hatch after a few hours or days. Midge life cycles vary tremendously depending on the species, but many have very rapid cycles such that they can produce many generations in a year. Some species emerge year round, especially during the winter months when there are several consecutive days of warm weather to stimulate larval growth and trigger an emergence. In short, a variety of midge fly patterns (larvae, pupae, and adults) covering a range of hook sizes should equip a fly fisher with a year round arsenal of fish catching imitations.

True bugs are not treated here in any great detail because, when compared to groups discussed above, they are of little importance to fly fishers. These insects belong to the order Heteroptera (or Hemiptera in some references) and are best characterized by their piercing-sucking mouthparts. True bugs exhibit a special type of hemimetabolous metamorphosis. Unlike mayflies where the nymph and adults do not resemble each other, the only noticeable difference between the nymphs and adults of true bugs is one of size. True bugs typically live lakes but can be found in slow moving parts of streams. The best known examples of aquatic true bugs include the water boatman (Family Corixidae) and water striders (Family Gerridae). Water boatmen use their hind legs, which are fashioned like a pair of oars to swim around. Water boatmen may also appear to have a silvery sheen around them. This represents an air bubble from which they breathe oxygen (sort of like a SCUBA for insects). Water striders are the spider-like insects that many people see skating on the surface of the water. True bugs are highly predacious and use their piercing mouthparts to inject a tissue-dissolving enzyme into their prey after which they suck out body fluids. Holding these insects in the palm of your hand can be a painful experience, especially if it is a member of the giant water bug family, Belostomatidae. Members of this family can reach a length of about 2 inches and have been known to capture small minnows!

WDTU maintains a teaching collection of aquatic insects collected by chapter member. The collection may be borrowed for study or use in a chapter outreach function. Interested individuals should contact Del Befus, WDTU Education Director, to arrange a loan. Specimens are stored in labeled vials containing 70 percent ethanol. A scientific species name consists of two parts, the genus name and the species epithet. Genus names should always be included when referring to a certain species because some groups of organisms can have species with the same epithet. For example:

Rhyacophila coloradensis — a caddisfly

Sweltza coloradensis — a stonefly

Malenka coloradensis — a stonefly

Clearly, it is unnecessary for a fly fisher to be versed in latin to understand aquatic insects. However, it can be useful when reading articles that sometimes overwhelm the reader with scientific names.

• Arctopsyche grandis "Net-Spinning Caddisfly"
• Claassenia sabulosa "Large Golden Stonefly"
• Hesperoperla pacifica "Large Golden Stonefly"
• Pteronarcys californica "Salmonfly"
• Tipula species "Cranefly larva"

• Pteronarcys californica "Salmonfly"
• Ameletus species "Dark Brown Dun Mayfly"
• Tipula species "Cranefly larva"
• Sigara species "Water Boatman"

• Hydropsyche occidentalis "Net-Spinning Caddisfly"
• Ephemerella inermis "Pale Morning Dun Mayfly"
• Baetis tricaudatus "Blue-Winged Olive Mayfly"
• Drunella grandis "Western Green Drake Mayfly"
• Tipula species "Cranefly larva"
• "Misc.Stonefly nymphs"
• "Misc. Stonefly nymphs and adults"

• Dicosmoecus gilvipes "Limnephilid Caddisfly"
• Arctopsyche grandis "Net-Spinning Caddisfly"
• Hydropsyche occidentalis "Net-Spinning Caddisfly"
• Ceratopsyche species "Net-Spinning Caddisfly"
• Brachycentrus americanus "American Grannom"
• Pteronarcys californica "Salmonfly"
• Drunella grandis "Western Green Drake Mayfly"
• Calineuria californica "Large Golden Stonefly"

LaFontaine, G. 1981. Caddisflies. Winchester Press, Piscataway, NJ, 336 p.

Leiser, E. and R.H. Boyle. 1982. Stoneflies for the Angler. Alfred A. Knopf, New York, 174 p.

McCafferty, W.P. 1981. Aquatic Entomology. Science Books International, Boston, MA. 448 pp.

Richards, C. and B. Braendle. 1997. Caddis Super Hatches: Hatch Guide for the United States. Frank Amato Publications, Portland, OR, 87 p.

Stark, B.P., S.W. Szczytko, and C.R. Nelson. 1998. American Stoneflies: A Photographic Guide to the Plecoptera. The Caddis Press, Columbus, OH, 126 p.

Stewart, K.W. and B.P. Stark. 1988. Nymphs of North American Stonefly Genera (Plecoptera). Entomological Society of American Thomas Say Foundation, Vol. 12. 460 p.

Ward, J.V and B.C. Kondratieff. 1992. An Illustrated Guide to the Mountain Stream Insects of Colorado. University of Colorado Press, Boulder, 191 p.

Wiggins, G.B. 1996. Larvae of the North American Caddisfly Genera (Trichoptera). University of Toronto Press, Toronto, 457 p.

There are thousands of Internet sites featuring aquatic insects and listing them here would be impractical. The best way to explore on your own is to search on a topic (for example, "caddisflies") using your web browser. Some links cater to professional entomologists while others are designed with the fly fisher in mind.