With the arrival of spring in Moscow comes an extremely thorough version of “spring cleaning.” The tasks of clearing streets and sidewalks of months’ worth of snow and ice — not to mention all the trash that has been buried under winter’s frosty deposits — falls into the calloused hands of the city’s dvorniki, or snow workers. Increasingly staffed by Central Asian immigrants who have moved to Moscow looking for work, this armada of cleaners hits the streets with shovels, picks and tractors every spring to help control the rivers of slush that appear when temperatures creep above freezing.