In the USA six species in this hard-to-spell burrowing mayfly family are known, and of those, only one species in California. For how large California is, only a few burrowing mayfly records have been published (see also Ephemeridae and Potamanthidae). Is this an artifact of collecting or something more interesting? Regardless, Meyer and McCafferty (2008) were the first to report this species (and this Family) from the state.
Ephoron album (Say)
Type Locale: Manitoba, Canada, although known from many western USA states.
California Distribution: Alpine Co.
Adult Description: Unfortunately there are no recently published keys for the adults. Day (1956) did include Ephoron, but you are better off using the Introduction to the Aquatic Insects of North America to ensure you get to the correct genus. The best figure for the male genitalia I have found is in Burks (1953). See Figs. 66 and 67 on page 34. The shape of the genitalia will get you to this genus quite readily, even allowing you to skip the key in the Aquatic Insect of North America. You can find a pdf at the Illinois Digital Environment for Access to Learning and Scholarship (https://www.ideals.illinois.edu/handle/2142/44737). This book was invaluable for my Masters degree, and even has some use in the western USA.
Larval description: As with the Ephemeridae, use McCafferty (1975) to key out the larvae. He provided a figure of the whole larvae (Fig. 31, drawn by Arwin Provonsha). Couplet 13 in his key will distinguish this species from E. leukon Williamson, the only other species in the genus found in the USA (albeit E. leukon is an eastern USA species and not likely to be found in California).
Identification Notes: Again, for the adults, to me the male genitalia are quite distinct, thus allowing me to bypass the keys. For the larvae, the tusks are also quite distinct–see Fig 31 in McCafferty (1975), but until you have seen them, one will have to use the keys.
Ecological notes: This is a well- studied mayfly. Google “Ephoron” and a number of ecological papers will come up. A few examples include: Giberson and Galloway (1985) studied the life history of this species in Canada. Other studies have been done by Edmunds (1948), Edmunds et al. (1956), and Phillips et al. (1994). On fly fishing pages this species is the “white mayfly.”
References:
Burks, B. D. 1953. The mayflies, or Ephemeroptera, of Illinois. Bull. Illinois Nat. Hist. Survey 26: 216 pp.
Day, W. C. 1956. Ephemeroptera. Pages 79-105 In Aquatic Insects of California. R. L. Usinger (ed). University of California Press, Berkley.
Edmunds, G. F. 1948. The nymph of Ephoron album (Ephemeroptera). Entomol. News 59:12-14.
Edmunds, G. F., L. T. Nielsen, and J. R. Larsen. 1956. The life history of Ephoron album (Say) (Ephemeroptera: Polymitarcidae). The Wasmann J. of Biol. 14:145-153
Giberson, D.J. and T. D. Galloway. 1985. Life history and production of Ephoron album (Say) (Ephemeroptera: Polymitarcidae) in the Valley River, Manitoba. Can. J. Zool. 63: 1668- 1674.
McCafferty, W. P. 1975. The burrowing mayflies (Ephemeroptera: Ephemeroidea) of the United States. Trans. Amer. Entomol. Soc. 101: 447-504.
Meyers, M. and W. P. McCafferty. 2008. Mayflies (Ephemeroptera) of the far western United States. Part 3: California. Trans. Amer. Entomol. Soc. 134: 337-430.
Phillips, E.C., R. V. Kilambi, and C. E. Carlton. 1994. Life History and Secondary Production of Ephoron album (Say) (Ephemeroptera: Polymitarcyidae) in the Illinois River, Arkansas Journal of the Kansas Entomol. Society Vol. 67: 242- 247