The snow fleas were out today. This is the second time this winter I’ve seen them. They often come out on warm sunny days in the winter by the thousands congregating in trails and footprints in the snow.
Snow fleas are a type springtail (order Collembola). These tiny soft-bodied invertebrates live in moist places like soil, moss or under forest duff. They have six legs like insects but are not true insects. Springtails differ by having only 4 or 5 abdominal segments, a tube called the collophore for obtaining water in addition to chewing mouthparts, and a forked appendage (furcula) on the last abdominal segment that can propel the animal into the air to escape.
Why the snow fleas come out onto the snow on sunny days in February or even January is not clear. Certainly, there is the risk of drowning in droplets of water on the snow or later freezing in the snow surface at night. Apparently, these migrations do not harm the population overall.
Other small invertebrates also come out regularly in the winter including a few species of spiders, small beetles, and a type of fly. None are as abundant as snow fleas, though. Sometimes I have come across very dense masses of snow fleas. My presence disturbs them and they begin to jump wildly. When I have gotten close to the snow and cupped my hands to my ears I can hear the snapping sounds made by all of those furcula going off at once.
Snow fleas are one of a few hundred species of springtails that live in northern temperate regions. They are extremely abundant despite their small size and number in the millions per acre of land. Such abundance would make them very important in the ecology of the soil. Many species eat bacteria, fungi, and decomposing matter. A few may be detrimental to agricultural crops but overall they provide more benefit to human activities than harm. Because they are sensitive to herbicides a large thriving population of springtails would indicate a soil free of these chemicals.