Ephemeroptera (Mayflies)

Most of the Ephemeroptera, Plecoptera, and Trichoptera (EPT) organisms are sensitive to changes in water quality. Their presence (or lack of) are good indicators of the health of our streams. They occur in all types of freshwater in the shallow areas where there is lots of oxygen. But, some mayflies and caddisflies are tolerant of stream degradation. You would have to identify these mayflies and caddisflies at the genus level to be sure.

Mayflies typically have 3 tails (occasionally two) and gills on the side of their abdomen. You have to identify them at the genus and some at the species level to know what their feeding habits (i.e. trophic functions) are. Their trophic functions can be "collectors, gatherers, scrapers, filter feeders, scavengers, or predators".

	Mayfly Photo: BC
Click on the picture to view it in more detail.

Note: Some mayflies have 3 tails and some have 2 tails. Therefore, it is important to use the tarsal claw as the identifier between mayflies and stoneflies.

• Mayflies have 1 tarsal claw, and
• Stoneflies have 2 tarsal claws
• Mayflies have plate-like or hair-like gills along sides of abdomen

The nymph comes to the surface only when it is ready to transform into a winged adult and reproduce.

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