Snow-surface activity of California Snow Scorpionfly, <i>Boreus californicus</i> (Mecoptera: Boreidae), in western Montana, USA

The flightless California Snow Scorpionfly (Boreus californicus Packard) has rarely been studied, and knowledge of its distribution and activity on snow remains fragmentary. I found it on snow surfaces in western Montana, USA, from valley grasslands to subalpine conifer forests and above the tree line. At lower elevations (991–1500 m), B. californicus was present on snow from early November to early March, at higher elevations (1800–2850 m), from early October to early January as well as late June. The species has now been documented in western Montana over an elevation gradient of nearly 2000 m and is probably active somewhere on snow in most months except in mid- and late summer. When the insect was present on snow, surface temperatures ranged from −5.0°C to 5.5°C. Pairs in copula (n = 26) were found when snow surface temperature was −0.5°C to 5.5°C. Mating occurred on snow at low elevations from November to late February, at high elevations in late June. The mating period in subalpine habitat, and probably above the tree line, includes early summer as well as late autumn to spring because of the colder temperatures and lingering snow in spring and earlier snowfall in autumn. Temperature and snow-cover characteristics affect the snow-surface ecology of B. californicus across its range in western Montana. Mating on a snow cover is likely related to greater mobility (ability to jump) on snow surfaces, aiding the search for mates and contributing to greater dispersal of eggs and reduced inbreeding.