Rise up, Lazarus: life history and distribution of the Arizona Snowfly, an intermittent stream specialist

Authors: Michael T. Bogan

Year: 2013 (xlv)

Abstract

Though intermittent streams are a dominant feature of southwestern landscapes, relatively little is known about their fauna, including the life history traits that allow this fauna to persist in streams that dry regularly. The Arizona Snowfly (Mesocapnia arizonensis, Plecoptera: Capniidae) was first described in 1969 from specimens collect by W.L. Minckley, among others, and for years was only know from a few streams. In recent years, however, I have collected the species from over 40 streams across Arizona and one stream in eastern California. The species appears to have been overlooked for so long because it prefers short flow duration (<4 mo/yr) streams, even when perennial water is present immediately upstream of its intermittent stream habitat. In highly arid basins, the Arizona Snowfly is only found during the heavy rains of El Niño winters and can remain in a desiccation-resistant dormant stage for up to five years before flow returns. In 2013, I documented the development and emergence of the Arizona Snowfly in Bear Canyon, Catalina Mountains, AZ and found that they emerge from dormancy within a couple weeks of flow resumption and can complete their nymphal development, emerge as adults, mate, and lay eggs all within a 7-week period. The species appears to only have one generation per year and abruptly stops development in early to mid-April, even when water quality conditions would allow for a longer growth period. Though widely distributed, this species’ future is intimately tied to El Niño events and abundant winter rains, which are forecast to decline under regional climate models.