This is quite an unusual group of mayflies in that the larva have what looks like a large carapace covering much of their bodies–you can see an example of this genus at the Digital Reference Collection of California Benthic Invertebrates found at the Aquatic Bioassessment Laboratory . Pescador and Berner (1981) is the key to use for identifying species of this genus–both adults and larvae.  In the western US only two species have been reported. Baetisca lacustris (see below) and B. columbianus Edmunds [Webb and McCafferty (2004) summarized and clarified these western records.)

Baetiscia lacustris McDunnough

California Distribution: Exact Location Unknown. The only published record of this species can be found in Eaton (1885), and I quote: “California (McLach Mus.)”. Not much to go on. McLach refers to Robert McClachan, another British entomologist who let Eaton examine this specimen. According to the obituaries written about McClachan (see The Entomologist’s Monthly Magazine, 1904, 40: 145-148 and in Nature, 1904, 70:106), his specimens went to the British Museum. But where in California was this specimen from? This is a good project for someone to work on.

Webb and McCafferty (2004) described how Pescador and Berner (1981) did not think species of this genus occurred west of the Rockies and thus all western records of Baetisca were a result of incorrect labels. Webb and McCafferty (2004) debunked this and in addition validated George Edmunds’ discovery of B. columbianus Edmunds in Washington. They also believed the California record was a valid record of B. lacustris (albeit this specimen was originally reported as B. obesa–just go see Webb and McCafferty for the full story).

Larval Identification: As there is only one species known from California, identification should be straight-forward if you happen to find one of these species. Pescador and Berner (1981) provided a key and excellent figures of the larvae (Figs. 13a and b). Just be sure to compare with Edmunds’ description of B. columbianus (see Edmunds 1960) to ensure it is not that species. His description is only for the larvae.

Adult Identification: Use Pescador and Berner (1981). As with the larvae, there are excellent figures of the diagnostic features of the adults. Again, when identifying this species, keep in mind. B. columbianus is also a western species–it is not yet known from California, but it seems a lot is not known about the distribution of Baetisca in the western US.

Eaton, A. E. 1883-1888. A revisional monograph of recent Ephemeridae or mayflies. Trans. Linnean Soc London Series 3: 1-352

Edmunds, G. F. 1960. The mayfly genus Baetisca in Western North America The Pan- Pacific Entomol. 36: 102-104.

Pescador, M. L. and L. Berner. 1981. The mayfly family Baetiscidae (Ephemeroptera). Part II Biosystematics of the Genus Baetisca. Trans. Amer. Entomol. Soc. 107: 163-228.

Webb, J. and W. P. McCafferty. 2004. New records of mayflies (Ephemeroptera) from Alberta, Canada. Entomol. News 114: 230-232.