Snow fleas are actually very tiny arthropods that may occur in many environments. They are commonly seen in the warmer months and are called springtails. Once considered insects, they have been assigned to their own classification as Entognatha Hexapoda, since they have many non-insect features.
Springtails have a unique method of locomotion, which gives rise to their name. The springtail has a fork-like structure, called a furcula, attached to the hind end that can fold under the body. Upon release, the furcula pushes the springtail into the air allowing it to jump short distances. Most are gray to purplish in color.
The great majority of springtails live in the soil, feeding on fungi, algae, decaying plant matter, and bacteria. They are pinhead sized and do not bite humans or pets. Found mostly outdoors, they may reproduce in tremendous numbers in moist soils with high organic matter. Occasionally they may migrate into houses if the weather is hot and dry, and will usually be seen in areas where there is moisture like sinks and bathroom drains. This is a nuisance but they will soon die after entering buildings.
Springtails will occasionally develop in the soil of houseplants after migrating in, or plants are brought inside for the winter. They do little, if any damage to the plant. Usually, allowing the soil to dry down a little more can reduce the problem.
Since this is the winter and we will (hopefully) be warming up soon, we can discuss the potential for seeing "snow fleas" when the snow (if we have any) begins to thaw. Since fleas jump, when people first began to see the snow flea phenomenon, they mistakenly thought the springtails were fleas, giving rise to the common name.
Springtails will develop under snow cover, feeding on leaf litter and soil. When the temperatures warm, the thawing snow will form channels from the soil to the snow surface along trees, old flower stems, and other vertical structures. The snow fleas may be so numerous as to show up like dirty spots, often in depressions made by footprints. A closer look will reveal the swarming, hopping critters. No one quite knows why this behavior occurs. It may be triggered by overcrowding in the litter beneath the snow, and as a possible response to warmer temperatures above the snow layer. Some may find their way back to the soil through the channels, but many will die.
Since we have had little snow cover to insulate the soil surface and some extreme temperatures, this may not be the best year to see snow fleas. You can look for them after we get one of our typical Nebraska February-March blizzards.
Much of this information comes from a Colorado State University fact sheet no. 5.602 "Springtails" by W. Cranshaw.