Baetis spp.

Mayfly. Photo from RMBL Archives
Baetis spp. are mayflies belonging to the family Baetidae. Adults have one or two sets of wings (depending on species) that align vertically above the body while at rest. Adults have two long tails off the end of the abdomen and short antennae. Males have large eyes used by swarming males to find females. Females do not have large eyes. The mouths of adult mayflies are nonfunctional and most live for only a few days after emerging. Baetis larvae are aquatic herbivores that drift downstream in search of food. The typical diet of Baetis larvae consists of algae growing on the surface of rocks.

Nymphs (larvae) are generally found in well oxygenated rocky bottomed streams. Adults are terrestrial and can be found near water. After mating, adult females lay their eggs under large rocks protruding from the surface of the water in fast flowing stream reaches.

Nymphs have gills along their abdomens that are used for obtaining oxygen from the water, and single claws on each of their six legs that help them adhere to rocks. Baetis larvae are excellent swimmers using short, rapid bursts by flexing their abdomens. Adult males have elongated forelegs and claspers, which are used to hold onto a female while mating.


Ecological Relationships
Baetis larvae are herbivores, feeding on microscopic algae, primarily diatoms. Mayflies serve as an important food source for trout as well as other insect predators such as stoneflies (Plecoptera).

Status and Conservation
The conservation status of different species of Baetis range from common to less common. The common species are Baetis bicaudatus, Baetis flavistriga, and Baetis tricaudatus.

Highlighted RMBL Research
Peckarsky et al. (2011), Why do vulnerable mayflies thrive in trout streams? American Entomologist 57 (3) pp. 152-164.

Encyclopedia of Life
Learn more about Baetis at the Encyclopedia of Life.

The Aquatic Insects of Gunnison County Colorado

Northern Rockies Natural History Guide, University of Montana at Missoula

Many thanks to Emily Thorne at Humboldt State University for this submission, and to RMBL Researcher Dr. Bobbi Peckarsky for her review and additions. Photo credit to Angus McIntosh for the Baetis bicaudatus photo.