Ephemeroptera (Mayflies)

views updated

Ephemeroptera

(Mayflies)

Class Insecta

Order Ephemeroptera

Number of families 37–40

Evolution and systematics

The scientific name of the order refers to the short life of the adult, or winged state. The English common name is associated with the month of May, when adults emerge more frequently in the Northern Hemisphere. The members of this order appear to be the most primitive of the extant flying insects. Fossil representatives that can be assigned to Ephemeroptera are known from the Upper Carboniferous, with some of the extinct groups (Bojophlebia prokopi) reaching gigantic sizes (a wingspan of up to 18 in, or 45 cm). Permian species had aquatic larvae, but unlike extant species, adults had functional mouthparts and pairs of wings of almost equal size.

The relationships of Ephemeroptera with other insect orders are still the subject of controversy. While some authors maintain that this order is related more closely to the dragonflies and damselflies (Odonata), forming the group Palaeoptera, others consider the Ephemeroptera basal to the other winged insect orders. The higher classification of the order is also questionable, with differing classifications at the suborder and superfamily levels. There are about 40 recognized fossil and extant families.

Physical characteristics

Body size ranges from very small (0.04 in, or 1 mm) to large (3.2 in, or 80 mm). Adults are of varying colors—white, yellow, pink, or black—generally with hyaline wings. Males generally are svelte, with the abdomen almost completely filled with air. The forelegs are always functional and very long. In females the body is more robust and stout, with the abdomen and part of the thorax filled with eggs. The hind wings can be absent, but when they are present, they always are smaller than the forewings. In some groups (e.g., Polymitarcyidae) the adult legs are nonfunctional with the exception of the first pair on the male; some leg segments may even be lost (e.g., the American genus Campsurus). The caudal filaments (two or three) are always present and are longer in males. While the overall appearance of the adults is remarkably standard, the larvae possess a wide variety of body shapes, ranging from depressed and shield-like among the swirl current dwellers to long and cylindrical among secluded tunnel inhabitants or spindle-like in the free-swimming forms.

A unique characteristic of Ephemeroptera is the presence of an extra winged stage, called the "subimago." It is similar to the adult stage, or imago, but the coloration is duller, the body more robust, and the wings usually smoky. This extra stage allows for the dramatic elongation of some parts of the body (male legs and genitalia). They are covered with water-repellent microhairs, which are important in allowing them to pass from the aquatic medium to the air.

Distribution

Cosmopolitan, except Antarctica, the extreme Arctic, and a few small oceanic islands.

Habitat

The larvae inhabit a wide variety of bodies of water, from swiftly running streams high in the mountains to lowland rivers, ponds, and lakes. Many live under rocks or debris, whereas others burrow in living or decaying plant tissues or the clay bottoms of rivers and lakes. Others swim freely in small ponds, and a few live in the film formed by water seepage. While most species are sensitive to pollution, some can tolerate a certain level of contamination of their habitat. For example, some species of the genera Callibaetis and Baetis

(Baetidae) can tolerate high contents of organic matter and relatively low oxygen, while some species of Caenis (Caenidae) can stand certain high levels of suspended sediments. The adults, which normally are weak fliers, stay close to the water, where immature insects live.

Behavior

Most larvae hide during the day to avoid predation, but some swim freely at this time. Some species are gregarious, especially those that live in restricted patchy environments, but no social structure is known. Adults spend most of the day resting in the shade of vegetation close to the water, until swarming time, at which point they fly actively.

Feeding ecology and diet

Mayflies feed only as larvae; mouthparts and the digestive system are atrophied in adults. Most larvae are detritivores or herbivores, but a few are predators. Some modifications of mouthparts or forelegs or both occur in some species of Oligoneuriidae and Polymitarcyidae that filter food. Larvae

of species living in tunnels filter food from the water current that is produced by the active movement of the abdominal gills. Mayflies are important components of the food chain; fish, birds, and invertebrates eat both adults and larvae. These insects are popular with fly fishermen, who tie flies to imitate certain species of larvae and adults and time their fishing to emergence patterns for best results.

Reproductive biology

The mating flight, or "swarm," of the male imagoes is one of the distinctive features of the order. The swarm time, location, flight pattern, and number of individuals participating are specific to each species. Some swarms are composed of a few males and others by hundreds of thousands. The female flies above the swarm and is taken by a male from below, using his long forelegs. Shortly after copulation the female deposits eggs in the water. The female can carry 100 to 12,000 eggs. Egg development ranges from one week to a year and the larval period from three weeks to three years.

Conservation status

Some species have a restricted distribution and strict ecological tolerance and are more endangered than are the widely distributed species. The main reasons for population decline are habitat degradation by pollution, deforestation of river margins, dam construction, and introduction of exotic fish. Two mayfly species are listed as Extinct and one as Vulnerable by the IUCN.

Significance to humans

The larvae, as primary consumers, filter and remove large amounts of nutrients from the water and are important as food for other aquatic organisms. Owing to their sensitivity to contaminants, mayflies are used as bioindicators of water quality. The winged stage facilitates nutrient and energy exportation from aquatic to terrestrial ecosystems. A few larvae burrow in wooden structures, and when some species that form massive swarms are attracted to town lights, they cause allergy-related problems for some people.

Species accounts

List of Species

Chiloporter eatoni
Brown mayfly
Stenonema vicarium

No common name

Chiloporter eatoni

family

Ameletopsidae

taxonomy

Chiloporter eatoni Lestage, 1931, Chile.

other common names

None known.

physical characteristics

Adult body size 0.6–0.9 in (15–22 mm); body and wings yellowish. Larvae have a big head and almost circular gills covering the abdomen. Gill color varies from pale yellow or pink to violet.

distribution

Southern Argentina and Chile.

habitat

Cold, well-aerated Patagonian creeks, streams, and lake margins.

behavior

Larvae can hide under rocks and debris, although they normally are agile crawlers and fast swimmers, using the gills to propel themselves. Adult behavior is unknown.

feeding ecology and diet

Larvae are active predators, feeding mainly on other aquatic insect larvae.

reproductive biology

Not known.

conservation status

Distribution very scattered. Populations probably are endangered by introduction of trout, owing to their large size, brilliant coloring, and conspicuous behavior.

significance to humans

Small, but important in fish diet.

Brown mayfly

Ephemera vulgata

family

Ephemeridae

taxonomy

Ephemera vulgata Linnaeus, 1758, Europe.

other common names

English: Brown drake.

physical characteristics

Adult grow to 0.5–0.9 in (14–22 mm) and have spotted wings. Larvae have mandibular tusks for burrowing and big abdominal fringed gills (directed dorsally) that produce a water current inside the burrow.

distribution

Europe, including Great Britain and Scandinavia, south of the Arctic Circle and eastward to central Siberia.

habitat

Mostly in still waters that are not too cold (ponds, lakes, and riverine estuaries) and slow-flowing lowland rivers.

behavior

Larvae burrow tunnels in silty and sandy substrates or in fine gravel. Imagoes fly in masses in the evening. Subimagoes hatch on the water surface.

feeding ecology and diet

Larvae are active filterers, feeding on small organic particles.

reproductive biology

Males form small to large swarms along shores. Females deposit their eggs while drifting on the water surface. The life cycle is completed within two (rarely three) years, depending on water temperature.

conservation status

Not threatened.

significance to humans

Small, but highly valued by fly fishermen, who tie flies that imitate larvae and adults. Fishing can provide high rental fees for water owners.

No common name

Stenonema vicarium

family

Heptageniidae

taxonomy

Baetis vicaria Walker, 1853, Saint Lawrence River.

other common names

None known.

physical characteristics

Adult body size is 0.4–0.6 in (10–14 mm); wings are hyaline with dark brown veins. Larvae are flattened, with broad head and spreading legs; caudal filaments longer than the body.

distribution

Eastern United States and southern Canada.

habitat

Variety of water habitats, generally in moderately to rapidly flowing streams of varying sizes.

behavior

Larvae are strongly thigmotactic (contact-loving), clinging to some substrates. They crawl rapidly but seldom swim, which they do poorly. The full-grown larva floats to the water surface, from where the subimago hatches.

feeding ecology and diet

Larvae are collectors (gatherers), feeding on particulate organic matter.

reproductive biology

Males form small swarms of 10 to 20 individuals. After mating, the female rests on the water, releasing eggs slowly or depositing a few at a time while touching the water with the tip of the abdomen. The life cycle lasts from a few months to one year.

conservation status

Not threatened.

significance to humans

Small, but important in fish diet.

Resources

Books

Berner, Lewis, and Manuel L. Pescador. The Mayflies of Florida. Rev. ed. Gainesville: University Presses of Florida, 1988.

Domínguez, Eduardo, ed. Trends in Research in Ephemeroptera and Plecoptera. New York and London: Kluwer Academic/Plenum Publishers, 2001.

Landolt, Peter, and Michel Sartori, eds. Ephemeroptera and Plecoptera: Biology, Ecology, Systematics. Fribourg, Switzerland: Mauron, Tinguely, and Lachat SA, 1997.

Needham, James G., Jay R. Traver, and Yin-Chi Hsu. The Biology of Mayflies, with a Systematic Account of North American Species. Ithaca, NY: Comstock Publishing, 1935.

Periodicals

Allan, J. Dave, and Alexander S. Flecker. "The Mating Biology of a Mass-Swarming Mayfly." Animal Behavior 37, no. 3 (1989): 361–371.

Brittain, John E. "Biology of Mayflies." Annual Review of Entomology 27 (1982): 119–147.

Edmunds, George F. Jr., and W. Patrick McCafferty. "The Mayfly Subimago." Annual Review of Entomology 33 (1988): 509–529.

Peters, William L., and Janice G. Peters. "In the Predawn Mass Mating of Sand-Burrowing Mayflies, Timing Is Everything." Natural History (1988): 8–14.

Ruffieux, Laurence, Jean-Marc Elouard, and Michel Sartori. "Flightlessness in Mayflies and Its Relevance to Hypotheses on the Origin of Insect Flight." Proceedings of the Royal Society London Series B. 265, no. 1410 (1998): 2135–2140.