They're Called Snow Fleas

Thanks Ken Hobson for letting me know what that large swarm of small bugs on the snow are.

They're snow flees.

He further notes:

"The Collembola or spring tails are fun to watch in the winter. The snow fleas are out on cold days feeding on pollen and spores laying on top of the snow. Odd group once thought to be insects.. now considered more like shrimp or crustacea.. enormously abundant. "

From Wikipedia:

"Snow flea"

A species of Sminthurinae(Symphypleona: Sminthuridoidea:Sminthuridae)

In sheer numbers, they are reputed to be one of the most abundant of all macroscopic animals, with estimates of 100,000 individuals per cubic meter of topsoil, essentially everywhere on Earth where soil and related habitats (moss cushions, fallen wood, grass tufts, ant and termite nests) occur; onlynematodes, crustaceans, and mites are likely to have global populations of similar magnitude, and each of those groups except mites is more inclusive: though taxonomic rank cannot be used for absolute comparisons, it is notable that nematodes are a phylum and crustaceans a subphylum. Most springtails are small and difficult to see by casual observation, but one springtail, the so-calledsnow flea (Hypogastrura nivicola), is readily observed on warm winter days when it is active and its dark color contrasts sharply with a background of snow.[2]