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Phylum Arthropoda
Class Insecta
Order Ephemeroptera
Family Caenidae
Common Name Small Squaregilled Mayflies
Distinguishing Characteristics
  • Gills on abdominal segment 1 small and finger-like
  • Gills on abdominal segment 2 plate-like and covering succeeding gills
  • Setae on caudal filaments restricted to apex on each annulation
Additional Pictures

     There are 4 generas of Caenidae found in North America. Larvae and adults range from 2-8 mm in length and can be found in streams in areas with slow moving currents. They can also be found at the water's edge of lakes and wetlands. Caenidae are catergorized as collectors/gatherers and scrapers.

     The operculate gills do not take up dissolved oxygen, but instead are used to cover and protect the other gills, which absorb dissolved oxygen from the water. Since these mayflies occur in areas where the current is slow, sediment can rapidly settle on the gills and prevent dissolved oxygen uptake. In order to keep the gills free of sediment, caenid mayflies wave their operculate gills.

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Additional Links



Merritt, R W., K W. Cummins, and M B. Berg. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa: Kendall/Hunt Company, 2008.