The Mayfly Analogy

Metamorphosis is a wonderful thing. It is physiologically compulsory for insects, many other invertebrates, amphibians, and some fish. It is a conscious choice in humans from the perspective of emotional, social, and intellectual maturity. Some people choose to remain forever neotenous, never advancing their ability to empathize with others, or accept that diversity and equality enhance our species rather than impede our collective evolution.

Small minnow mayfly, Callibaetis sp., Mueller State Park, Colorado, USA

Mayflies, aquatic insects in the order Ephemeroptera, are best known for their ephemeral adult lifespans, often only a day or two, several days maximum, and as short as one hour. As underwater naiads, their youth may last three months to three years, depending on the species.

Mayflies are the only insects that molt after reaching adulthood. The naiad emerges from the water, splits its exoskeleton down the middle of the thorax, and a winged insect slowly draws itself out. This is the subimago, or “dun” in the parlance of anglers who model their imitation flies after certain mayflies.

The dun flies to another perch, such as foliage overhanging the water, or a bridge abutment, or similar platform. There, it repeats the molting process, becoming a fully-fledged, sexually mature imago that fly fishermen call a “spinner.” These adults lack functional mouthparts, as there is no time for feeding. There is only mating and, in the case of females, laying eggs. At least one species, Cloeon dipterum of the British Isles, births live naiads, having incubated the eggs within her body.

Common burrower mayfly, Hexagenia sp., along the Missouri River in Leavenworth, Kansas, USA

The evolutionary origin of mayflies dates back to the middle of the Carboniferous Period in the Paleozoic Era, about 325 million years ago. This places them near the most basal root of the phylogenetic tree of all winged insects.

The Ephemeroptera are the “E” in EPT, a biological index that informs water quality in environmental health assessments. Together with stoneflies (Plecoptera) and caddisflies (Trichoptera), mayfly naiads vary in their sensitivity to pollutants, overly turbid, and warmer-than-normal streams, rivers, and lakes. Generally, the more species diversity in these insect orders in a given watershed, the healthier the aquatic ecosystem is.

Our own children thrive best in environments devoid of toxic ideologies, and well-oxygenated with empathy, equality, justice, and peace instead of turbidity. The more diverse our neighborhoods, schools, and institutions are, the better.

True, the naiads of prongill mayflies, in the family Leptophlebiidae, ensconce themselves in crevices and shun the light, and burrowing mayflies in the family Ephemeridae tunnel into the silt or sand of streambeds and lake bottoms. That does not mean we should bury our own heads in the sand, stubbornly clinging to outdated social strategies that further divide us.

Small square-gilled mayfly, Caenis sp., Colorado Springs, Colorado, USA

Adult mayflies often emerge synchronously, in overwhelmingly abundant “hatches” that anglers attempt to time appropriately with their feather-and-thread imposters. Major rivers are often the site of these eruptions, and the Great Lakes are beginning to see a resurgence in numbers that have been at a historic ebb for decades thanks to pollution. Bulldozers are often necessary to sweep the dead insects from roadways lest they become a slick, greasy hazard.

Homo sapiens has been on this planet for barely the geological equivalent of one day, so perhaps we are all subimagos, having not yet graduated to full adulthood in appreciation of our own diversity. I like to think that I have entered that stage, aware, yet still awkward in my attempts to help others out of their own prejudicial entanglements, their ecdysis mired and twisted by privilege and entitlement.

Maybe I’m wrong. Maybe I am a cicada, and thirteen or seventeen years hence I will realize I knew nothing. Still, the idea that just when you thought you were done, you are only a dun, resonates more. We may never arrive, never become spinners, but we are certainly farther away than we think we are.

A "slate drake" mayfly, Isonychia sp., from Leavenworth, Kansas, USA

Sources: Fauceglia, Ted. 2005. Mayflies: Major Eastern and Midwestern Hatches. Mechanicsburg: Stackpole Books. 196 pp.
Grimaldi, David, and Michael S. Engel. 2005. Evolution of the Insects. Cambridge: Cambridge University Press. 755 pp.
McGavin, George C. 1998. The Pocket Guide to Insects of the Northern Hemisphere. London: Parkgate Books, Ltd. 208 pp.

Review: Diving Beetles of the World

Johns Hopkins University Press is an underrated publisher of natural history titles for both professional scientists and general audiences. Their latest example of impeccable quality is the book Diving Beetles of the World: Systematics and Biology of the Dytiscidae, by Kelly B. Miller and Johannes Bergsten. It is somehow fitting that a relatively ignored family of aquatic beetles gets its "coming out party" delivered by a publisher assumed to be mostly a purveyor of medical books.

Diving Beetles of the World should be a model for a serious and thorough treatment of any entomological subject. Every aspect of the biology, ecology, and classification of the family Dytiscidae is covered here. It is this placement of the beetles in a larger context that is so vital, and so often lacking in other technical publications devoted to various insect taxa. Creating an appreciation for a neglected family of organisms is no small feat, and this publication vastly exceeds expectations.

Rhantus gutticollis from Colorado

It helps greatly that the book is lavishly illustrated with detailed images of perfectly prepared specimens of the beetles themselves. Even a casual student of entomology will feel comfortable at once. Furthermore, keys to the subfamilies, tribes, and genera of diving beetles are likewise illustrated with line drawings and clear, magnified images of critical parts of the beetles' anatomy. Were that not enough, there are also maps showing the global distribution of each genus.

The summary for each genus includes a "diagnosis" of physical characters peculiar to that genus, in case you missed anything during your journey through the keys; a history of classification and relationships to other genera; a description of diversity that includes the number of species currently recognized for that genus; a natural history indicating what habitats and niches the particular genus occupies in nature; and finally a distribution description that complements the maps.

Thermonectus marmoratus from Arizona

The authors, one American and one European, fully recognize the fluid nature of insect taxonomy and have cited virtually every paper and publication written previous to this current work. This sets the stage perfectly for ongoing and future investigations into the Dytiscidae.

Considering that aquatic ecosystems are arguably the most critical habitats on the planet, this book deserves to have an impact far beyond entomology. Every aquatic biologist, environmental consultant, and citizen scientist needs to have this volume in their library, or at least seriously consider it. Should you not make the purchase yourself, please suggest it to your university library.

Colymbetes sculptilis from Massachusetts

Indeed, the only unfortunate aspect of this tome that does not recommend it is the price: $150.00 U.S. Easy for me to enjoy my review copy while my readers are looking at a major expense, no doubt. Still, this is an important work, not just a gift for "the entomologist or naturalist who has everything." How to reconcile quality work with an affordable sale price is a question for another blog, and believe me I am open to suggestions. In the case of Diving Beetles of the World, the product commands the monetary value assigned to it.

Note: Images other than the book cover are my own and are not featured in the book.

Mini-mantises: Ochthera Shore Flies

Mantids (aka "praying mantises") are widely acclaimed for having the strongest grip among predatory insects, but many other insects have similar modifications to their front legs that afford them a vise-like purchase on struggling prey. Among the more unusual of these are shore flies in the genus Ochthera, found over most of North America.

I was delighted to discover some of these flies recently here in Colorado Springs, where they favor very shallow, trickling streams with algal mats and other debris they can run around on in search of other small insects.

Ochthera are small, only 4-5 millimeters in body length. They are squat and compact, with triangular faces and somewhat protuberant eyes. Their most obvious feature is the pair of front legs, with an enlarged coxa (segment connecting the leg to the thorax), greatly enlarged and muscular femur ("upper arm" if you will), and curved, blade-like tibia ("forearm" comparison to a person). The tarsi ("feet") are of normal appearance. The forelegs are thus raptorial, meaning heavily modified to sieze prey. Spines and tiny teeth on the inside of the femur help anchor the victim between femur and tibia.

The flies easily overpower other small insects such as midges, mosquitoes, and leafhoppers that alight on the shore or the surface of the water. They can also unearth midge larvae from the muck along the shore.

Watch one of these flies and you will see it periodically "stretch," reaching out, flexing, and waving those front legs. This may be a threat display directed at other members of its own species, or a means of recognizing each other and avoiding cannibalism (Simpson, 1975). Females may literally lash out at males attempting to mate with them. Males attempt to mount females from the rear, jumping on top of them and gripping the female's "shoulders" if they are not rebuffed. He sets the mood by rapidly tapping the sides of her abdomen with his hind feet. Actual mating can last at least five minutes, at least in one species (Deonier, 1972).

Mated females lay eggs singly, usually on dead, water-logged, or partly submerged grass stems at the shore or in the shallows. Larvae of Ochthera are aquatic or semi-aquatic, and likewise predatory; they feed mostly on midge and mosquito larvae that they coil around like a snake constricting a rat. They have mouthparts that penetrate the exoskeleton of their prey and feed on soft internal tissues. Larvae progress through three instars (an instar is the interval between molts), before pupating. The pupal stage is also aquatic, equipped with breathing tubes. The larval stages last an average of 7-11 days, the pupal stage about 7-10 days. Egg to adult thus takes about 16-21 days, at least under laboratory rearing conditions.

Look for Ochthera adults from the end of March through the end of October in appropriate habitats. There are thirteen species known for North America, collectively distributed over most of the continent.

Sources: Deonier, D.L. 1972. "Observations on Mating, Oviposition, and Food Habits of Certain Shore Flies (Diptera: Ephydridae)," Ohio J. of Sci. 72(1): 22-29.
Simpson, Karl W. 1975. "Biology and Immature Stages of Three Species of Nearctic Ochthera (Diptera: Ephydridae)," Proc. Entomol. Soc. Wash. 77(1): 129-155. This is an excellent, well-illustrated paper.
Winkler, Isaac. 2011. "Insect of the Week - number 57," Insect Museum, North Carolina State University.

Backswimmer or Water Boatman?

Just a short post for “True Bug Tuesday,” addressing an identification problem that many people admit having. I am not an expert on aquatic insects by any means, but differentiating backswimmers (family Notonectidae) from water boatmen (family Corixidae) is fairly straightforward.

Backswimmer swimming upside down

My own experience has shown that backswimmers are generally far more commonly seen by the casual observer than are water boatmen. Backswimmers can even turn up in the fountains, swimming pools, and other artificial water environments water boatmen rarely frequent. Now, if you bother dragging a net through the water, especially over the bottom of a pond or slow-moving stream, then you may see water boatmen at least as frequently as backswimmers, if not more so.

Turn on lights at night anywhere near water and you may bet large numbers of water boatmen showing up, flailing about on the ground. Both water boatmen and backswimmers can fly as adults, but backswimmers seem to be mostly diurnal and will rarely if ever be attracted to lights at night.

Water boatman attracted to light at night

Physically, both kinds of insects do superficially resemble each other. Both are more or less oval or bullet-shaped, and the hind legs are very long, modified for rowing through the water. That is pretty much where the similarities end, however.

Adult backswimmers, at least those of the common genus Notonecta, are much larger than the average water boatman. Backswimmers, in cross section from front to back, have distinctly triangular bodies. They are shaped more like a boat than a water boatman. The top of a backswimmer is keel-like, affording it the ability to swim very rapidly upside down. Water boatmen are more flattened top to bottom.

Water boatman

The front legs of backswimmers are short, but shaped normally, with no obvious modifications. The front legs of water boatmen have spoon-shaped tarsal segments for scooping organic matter into the mouth of the bug. While backswimmers have a four-segmented rostrum (“beak”) they use to bite prey, water boatmen have the beak fused to the head. The face of a water boatman reminds one of an imperial storm trooper from Star Wars.

Water boatman. Note scoop-like front "feet"

Most water boatmen are brown on top, marked with fine, transverse black lines, giving them a slightly corrugated appearance. Backswimmers, by contrast, are usually boldly marked with patches of black, yellowish-brown, red, or white.

Top of backswimmer, © Lynette Schimming

Backswimmers frequent open water where they actively pursue mosquito larvae and other small aquatic insects. Water boatmen normally cruise the bottom, stirring up muck and microscopic organisms that they feed on. Consequently, water boatmen are often difficult to see when you are looking into the water. They are camouflaged, and/or they hide under leaf litter and other bottom debris.

Backswimmer, © Margarethe Brummermann

Look for backswimmers surfacing to take in air with those hydrophobic hairs around their rear end. The hairs also go down the middle of the underside of the abdomen, helping to trap air for their underwater lifestyle.

Source: Lehmkuhl, Dennis M. 1979. How to Know the Aquatic Insects. Dubuque, Iowa: Wm. C. Brown Company Publishers. 168 pp.

Forestflies (Spring Stoneflies)

Ever since we decriminalized the sale of marijuana in Colorado, people here seem to think that “stonefly” is a term that describes an insect trapped in a bong. That would be a stoned fly. Anglers know the difference, and right now is the time for “hatches” of spring stoneflies in the family Nemouridae along the Front Range.

The species I find most commonly probably belong to the genus Zapada, known as “forestflies.” I haven’t bothered to catch any specimens and turn them over. The cervical (“neck”) gills of the larval stage (nymph or naiad) are retained by the adult and are diagnostic. Two sets of branched gills on each side of the body mean it is in the genus Zapada.

© Arlo Pelegrin via Bugguide.net

Stoneflies in general are excellent indicators of water quality in streams and rivers because they are more sensitive to pollution, dredging, and other alterations to their habitat than many other aquatic insects. Spring stoneflies, which are also known as “little brown stoneflies,” are tolerant of a moderate amount of pollution and other human disturbance.

© J. Bodenham in Ward & Kondratieff, 1992

Nymphs of Zapada cling to submerged rocks and other heavy objects in flowing waters. There is one generation per year for the common species Z. cinctipes, meaning it is “univoltine.” Some other species require 2-3 years to complete their life cycle. The nymphs feed on vegetable matter, mostly leaves that fall into the water. Aquatic insects that chew up leaves are known as “shredders.”

© Tim Loh via Bugguide.net

Adult forestflies can begin emerging as early as late February, but most have their peak emergence from mid-March to mid-April. Mature nymphs, and adults, measure only 5-8 millimeters in body length (not including the wings of the adult), so these are not conspicuous insects. Adults are most often seen on bridges or logs that stretch across streams and creeks. They are quite active, running rapidly and flying when startled.

Considering the rich history of mining in the Pikes Peak region, and various chemical spills that have contaminated the few creeks and rivers here in Colorado Springs, I am rather surprised that forestflies continue to prosper.

Sources: Adams, Jeff and Mace Vaughan. 2003. Macroinvertebrates of the Pacific Northwest: A Field Guide. Portland, Oregon: The Xerces Society. 16 pp.
Brown, Wendy S. 2005. “Plecoptera of Gunnison County, Colorado,” The Aquatic Insects of Gunnison County, Colorado.
Stewart, Kenneth W. and Bill P. Stark. 1993. Nymphs of North American Stonefly Genera (Plecoptera). Denton, Texas: University of North Texas Press. 460 pp.
Ward, J.V. and B.C. Kondratieff. 1992. An Illustrated Guide to the Mountain Stream Insects of Colorado. Niwot, Colorado: University Press of Colorado. 191 pp.

Snail-killing Flies, genus Sepedon

You never know where learning the life cycle of an insect will take you; or how it might advance prevention of parasitic diseases on another continent. In this special procrastination edition of “Fly Day Friday,” we take a look at the fascinating fly genus Sepedon in the marsh fly family Sciomyzidae.

I was reminded of the strange lives of marsh flies when Heidi spotted one while we were walking our dog on an urban trail beside Fountain Creek in south Colorado Springs on February 24 of this year. I was surprised to see a specimen of Sepedon this early in the year, but there it was (image above).

There are twenty species of Sepedon currently recognized in North America (Knutson and Orth, 2001). These species are arranged in “species groups,” based on shared characteristics.

What is truly captivating is not the taxonomy (classification) of these flies, but their life cycle. The larvae of all Sepedon species are predators of aquatic pulmonate snails. These are air-breathing mollusks that have a simple lung in addition to, or instead of, gills.

Killing and eating snails is not without its risks. The fly larvae live just beneath the surface of the water, suspended by water-resistant hairs surrounding their posterior spiracles (breathing holes). The snails attacked are species without an operculum, the hardened plate that can seal the animal firmly inside its shell. So, a predatory fly larva won’t have the door slammed in its face when launching an attack. Still, the maggot can become suffocated by mucous excreted by the snail in self-defense; and the water-repellent hairs on the larva can get enmeshed in snail feces (Maharaj, et al., 1992).

Despite such perils, the fly larvae are efficient predators. Different lab studies have shown the larvae of different species can consume, individually, anywhere from eight to nearly fifty snails. Granted, many victims are very small. Indeed, the successful completion of a Sepedon life cycle depends on the availability of juvenile mollusks as prey for the first and second instars (an instar is the interval between molts). The third (and final) instar larva can take substantially larger snails.

Sepedon larva (A); posterior spiracles (B); anterior segments (C) ©Valley City State University, North Dakota

In the tropics, some aquatic snails are hosts of parasites, particularly schistosomes that can affect humans directly, and livestock liver flukes. Consequently, control of these snails is desirable. The possibility of employing snail-killing flies as biocontrol agents has been pursued with some vigor, but the few field trials have yielded mixed results.

Once a larva matures, it pupates. The puparium is capsule-like and boat-shaped, upturned at the posterior end, the better to float amidst organic matter at the margins of ponds or the shores of flowing waters. An adult fly emerges sometime later (a cursory search yielded no duration for the pupal stage).

Male flies have the tibia of the hind leg bowed in shape, and the hind femur swollen and armed with teeth. These features help embrace the female during courtship and mating. The general appearance of both genders is a more-or-less “stretch limo” of the fly world, sleek and slender, with a concave face and jutting antennae.

Mated females deposit small numbers of eggs in masses on emergent vegetation, so look for these insects in swampy areas, along the edges of ponds, and the banks of streams and rivers, even drainage ditches. A water course need not be flowing permanently to host both the flies and their snail prey. The adult flies overwinter, too, which explains how Heidi managed to find one so early this year.

Sources: Fisher, T.W. and R.E. Orth. 1983. “The Marsh Flies of California (Diptera: Sciomyzidae),” Bull. California Insect Survey vol. 24, 1-117.
Knutson, Lloyd Vernon and Jean-Claude Vala. 2011. Biology of Snail-killing Sciomyzidae Flies. Cambridge: Cambridge University Press. 526 pp.
Knutson, L. and R.E. Orth. 2001. “Sepedon mcphersoni, N. Sp., Key to North American Sepedon, Groups in Sepedon s.s., and Intra- and Intergeneric Comparison (Diptera: Sciomyzidae),” Proc. Entomol. Soc. Wash. 103(3): 620-635.
Maharaj, R., C.C. Appleton, and R.M. Miller. 1992. “Snail predation by larvae of Sepedon scapularis Adams (Diptera: Sciomyzidae), a potential biocontrol agent of snail intermediate hosts of schistosomiasis in South Africa,” Med. Vet. Entomol. 6(3): 183-187.
Neff, S.E. and C.O. Berg. 1966. “Biology and Immature Stages of Malacophagous Diptera of the Genus Sepedon (Sciomyzidae),” Blacksburg, VA: Virginia Polytechnic Institute, Agricultural Experiment Station Bulletin 566. 113 pp.
images of larva from Valley City State University, Valley City, North Dakota, Macro-invertebrate Lab, Digital Key to Aquatic Insects of North Dakota.