Mayflies: Ephemeroptera

views updated

MAYFLIES: Ephemeroptera

NO COMMON NAME (Chiloporter eatoni): SPECIES ACCOUNTS
BROWN MAYFLY (Ephemera vulgata): SPECIES ACCOUNTS

PHYSICAL CHARACTERISTICS

Mayflies range in length from 0.04 to 3.2 inches (1 to 81.2 millimeters). They come in a variety of colors, including white, yellow, pinkish, gray, or black. The adults always have wings. In fact, this is the oldest group of winged insects alive today. One mayfly fossil (FAH-suhl), an impression of a mayfly left in mud in ancient times and hardened into stone, has a wingspan of 18 inches (45.7 centimeters). The four transparent wings of the mayfly are held together straight over the body. A network of veins supports each wing. The first pair of wings is much larger than the second; in some species the second pair of wings is very small or even missing altogether.

Males and females are usually easy to tell apart. Males have eyes that are each divided into two separate parts. The upper parts of the eyes are directed upward and mounted on short stalks. The eyes are very sensitive, so males can easily find and capture female mayflies in mating swarms or when there is little sunlight. Males have long front legs that are held out in front of the body. They also have slender bodies, and the abdomen is filled mostly with air. Females are shorter and have heavier bodies, and their abdomens are filled with eggs. The abdomens of both males and females are tipped with two or three long, threadlike structures that are used like antennae (an-TEH-nee), to help mayflies "feel" what is going on behind them. These structures are always longer in the males.

Although adult mayflies are amazingly similar to one another, their larvae (LAR-vee) come in a wide variety of shapes. They do not resemble adults. Species living in fast-moving water cling to rocks and are usually flat and shieldlike in shape. Their low, smooth bodies prevent them from being swept away by the swift current. Mayfly larvae living in the slower waters of ponds and lakes are usually free-swimming. Their bodies are slender and shaped more like a cylinder. No matter how and where they live, all mayfly larvae have chewing mouthparts.

The larvae breathe underwater with gills. The gills are attached along the sides of the abdomen. Depending on where they live and the oxygen content of the water, the gills are brushy and tuftlike or flattened into plates. Species with feathery gills often live in low-oxygen water, and the feathery gills have more surface area exposed to the water, for drawing in the oxygen. Species with flattened gills usually live in fast-moving streams. Their streamlined shape prevents them from being swept away by the current. In some species that live in fast-moving water, the gills form a sticky disk that acts like a suction cup to attach the larvae to submerged rocks. Other species use their gills as paddles for swimming.

GEOGRAPHIC RANGE

Mayflies are found on all continents except Antarctica and a few small islands in the middle of the ocean. They are most abundant in mild or tropical climates.

HABITAT

The larvae live in a wide variety of freshwater habitats, from swift mountain streams to lowland rivers, ponds, and lakes. Many live under rocks, logs, and other debris (duh-BREE). Some species burrow in living or decaying plant tissues or in the soft, muddy bottoms of rivers and lakes. Others swim freely in small ponds or in small springs and seeps, pools where water has oozed to the ground surface. Most species are sensitive to pollution, or poison, waste, or other material that makes the environment dirty and harmful to health. Some are tolerant of small levels of contamination in the form of plant debris, animal waste, and muddy water. Adults are weak fliers and usually stay very close to the body of water where they grew up.

DIET

Mayflies feed only as larvae. By the time they reach the adult stage, their mouthparts and digestive systems have mostly disappeared. Most larvae eat bits of living or dead algae (AL-jee) from the bottom of their water habitat. Burrowing species flap their abdominal gills to draw water into their burrows. They use their mouthparts and legs to strain out bits of algae from the incoming water. Other species scrape algae off rocks and logs with their mouthparts. A few species attack and eat the aquatic, or water-living, larvae of flies.

BEHAVIOR AND REPRODUCTION

Mayfly larvae are important in transferring energy in freshwater habitats. The larvae strain and eat large amounts of algae as food. They transfer the algae's energy to other animals when fishes, birds, insects, and spiders eat them.

Most larvae remain hidden during the day to avoid predators (PREH-duh-ters), or animals who hunt them for food, but others are found swimming out in the open in the daytime. Some species live in groups, especially in puddles and pools that last for only a short period of time. They usually come out of the water at dawn or just before nightfall to transform into adults, but some species leave the water at midday. Males usually surface well before the females.

Adult male mayflies sometimes take part in massive mating flights. The time, location, flight pattern, and number of participating mayflies vary with each species. Some swarms are composed of a few males, and others have hundreds or even thousands of mayflies. Females fly above the swarms and are spotted by the males swarming below. Males use their long front legs to grab the females. Sperm is transferred to the female directly. After mating, the female lays one hundred to twelve hundred eggs in the water.

MAYFLIES ON THE COMEBACK TRAIL?

More than one hundred years ago many European rivers were the sites of spectacular swarms of mayflies numbering in the thousands every year. Since then, many populations have declined drastically or disappeared entirely. Scientists blame water pollution and larval habitat destruction caused by heavy industries located on the rivers. As factories in Communist countries started closing in the early 1990s, the water quality of many rivers in Eastern Europe began to improve, giving some mayfly populations a chance to increase their numbers.

Mayflies spend most of their lives in the water as eggs and larvae. The eggs take one week to one year to hatch. In most species the larvae molt, or shed their external skeletons, fifteen to twenty-five times before reaching adulthood. Depending on the species and local conditions, such as temperature and water quality, mayfly larvae take from three weeks to three years to reach adulthood.

Mayflies are the only order of insects that has an extra winged stage called the "subimago" (sub-ih-MAH-goh) The subimago is duller in color than the adult, or imago. It is also heavier bodied and has wings that are smoky instead of clear. The subimago is covered with water-repellent hairs that allow it to emerge from the water unharmed in preparation for adult life on land. At this stage, the mayfly has lost its larval gills and would be in danger of drowning as it makes its way to the surface, if it were not for the hairs, which keep water away from the mayfly's breathing holes. The adults live only a few days, just long enough to mate and lay eggs.

MAYFLIES AND PEOPLE

Because of their sensitivity to changes in the water, larval mayflies are often used by scientists as indicators of water quality. Their presence or absence in ponds, lakes, streams, and rivers may give evidence of changes in water temperature, oxygen levels, or chemical pollution. Mayflies are also popular with fly fishermen. They make lures called "flies" that imitate the forms of both adult and larval mayflies, using them instead of living bait to get fish to bite.

CONSERVATION STATUS

The World Conservation Union (ICUN) lists two species of mayflies as Extinct, meaning that no members of the species are still alive, and one as Vulnerable, meaning that it faces a high risk of extinction in the wild. The main reasons for declining populations of mayflies are habitat destruction by pollution; deforestation, or the clearing of land of trees, at the margins of rivers; dam construction; and introduction of foreign fish.

NO COMMON NAME (Chiloporter eatoni): SPECIES ACCOUNTS

Physical characteristics: Adults are 0.6 to 0.9 inches (15.2 to 22.9 millimeters) in length. Their bodies and wings are yellowish. The larvae have large heads and almost circular gills covering the abdomen. The gills vary in color from pale yellow or pink to violet.

Geographic range: This species lives in southern Argentina and Chile.

Habitat: They live in cold, fast-flowing creeks and streams as well as the borders of lakes with well-oxygenated water.

Diet: The larvae are active predators and eat the larvae of other aquatic insects.

Behavior and reproduction: The larvae crawl on the bottom and are fast swimmers. They use their gills to propel themselves through the water. When they are not feeding, they hide under rocks and other debris. The behavior of adults, including reproduction, is unknown.

Chiloporter eatoni and people: They do not affect people or their activities directly.

Conservation status: The World Conservation Union (IUCN) does not officially list this species, but their populations may be threatened by the introduction of insect-eating trout. ∎

BROWN MAYFLY (Ephemera vulgata): SPECIES ACCOUNTS

Physical characteristics: Adults are 0.55 to 0.86 inches (14 to 21.8 millimeters). Their wings are spotted. The larvae have mouthparts that look like miniature elephant tusks. They use these tusklike jaws for burrowing in the mud. The large abdominal gills are fringed and used, in part, to create a water current inside the burrow, as a way to maintain a steady flow of oxygen-rich water and food particles.

Geographic range: The brown mayfly lives in western Europe, including Great Britain and Scandinavia, and areas south of the Arctic Circle, ranging east to central Siberia.

Habitat: The larvae prefer the still waters of ponds, lakes, slow-moving rivers, and the mouths of rivers that are not too cold.

Diet: The larvae strain bits of algae and plant materials from the water with their mouthparts and legs.

Behavior and reproduction: Larvae burrow in muddy and sandy bottoms or in fine gravel.

Males fly in small to large mating swarms in the evening next to bodies of water. Females lay their eggs while they float downstream on the water surface. The life cycle is completed within two, or, rarely, three years, depending on water temperature.

Brown mayflies and people: Brown mayflies are valued by fly fishermen, who tie flies that imitate the body form of both larvae and adults.

Conservation status: This species is not threatened or endangered. ∎