Mayflies (Ephemeroptera)

1. Identification and Characteristics:

There is only one small species of mayfly in Emigration Creek. It is not abundant, but has been found in small numbers during the last several years. It is probably a low elevation species of the genus Baetis (family Batidae) in the United States. They are common and widely distributed (Pennak, 1978). Some Characteristics of the Batidae family larvae are:

     - small usually 3-12mm when mature

     - head is vertically oriented and antenna are usually longer than twice the           head width.

     - hindwing pads are absent or minute

     - platelike gills

     - two or 3 tails, also known as anal cerci

2. Development:

The metamorphosis of a mayfly is incomplete. Larval (or nymph) development time can range anywhere from a few weeks to two years. This development time depends on the species and local climate. Eggs and larvae can go through periods of non-development. This is more common at higher elevations and more northern latitudes. Once the larvae have reached maturity they make the transition from aquatic to terrestrial habitats. This period is often called a hatch, and occurs after a varying number of instars (developmental stage of a larva) prior to the final exoskeleton shedding and the emergence of the winged adult. Adults generally do not live longer than a month, and are non-feeding during that time.

3. Habitat:

Mayflies can be found in almost all natural and many artificial bodies of freshwater is there is an adequate oxygen supply. Different species prefer different substrates, temperatures, and speed of the flowing water.

4. Special Adaptations:

The gills of the mayfly contribute significantly to the total amount of body wall surface area available for oxygen up take. In some species, a pulsating movement of the abdomen creates a current that provides a flow of oxygenated water over the gills, as well as food particles to the mouth.

5. Importance of the Mayfly in Water Quality:

The mayfly is an important indicator of water quality, temperature, and dissolved oxygen content.  Most mayflies live in only the cleanest water. Many streams in the Rocky Mountains have several species, yet lower Emigration Creek has only one. This could be a sign that the water quality of the creek is not as clean as it could be.

6. The Mayflies Place in the Food Web:

Mayflies, with a few exceptions are detritivores (meaning they feed on dead organic matter) and/or herbivores. They feed on microscopic algae, diatoms, and small bits of organic matter. The Emigration Creek Baetis seem to be associated with decomposing leaves which accumulate in the creek in late fall. Some common predators of the Mayfly in the Emigrations creek are trout and water striders. When the flying adults lay their eggs on the water's surface, or when the adults emerge from instar larval cases, they provide a  major food source for trout.

7.  Mayflies and Fly-Fishers:  Both the adults and larvae of mayflies, caddisflies, and stoneflies are important food sources for Rocky Mountain trout species.  Fly fishers use artificial lures which simulate both the juvenile larvae (wet flies) or the reproductive winged adults (dry flies).  A knowledge of both the trout and the local mayfly, caddisfly, and stonefly species are critical for the successful fly fisherpersons.



     McCafferty, Patrick W., 1983. Aquatic Entomology. Jones and Barlett Publishers Inc., Sudburg, MA.

     Pennak, Robert W., 1978. Freshwater Invertebrates of the United States (2nd ed.). Wiley-Interscience Pub.

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