Yesterday was the kind of day when you could not take a step without knowing you were crushing hundreds of Snow Fleas, or Collembola, those tiny black specks on the snow. Their presence is a hopeful sign in northern New England, as it often signals the coming of spring, which we are more than ready for.
This non-insect arthropod is a type of springtail (not a flea). Springtails are no longer considered insects, but are classified as hexapods. These miniscule creatures sometimes come to the surface of the snow on warm winter days but are active year-round in leaf litter, feeding on algae, fungi and decaying organic matter.
Snow Fleas do not bite, nor do they sting. What they do do is catapult themselves impressive distances by means of an appendage on their underside called a furcula which snaps and propels them through the air. They have a soft landing due to three anal sacs that they evert from their anus just before launching themselves. (To see a photograph of these sacs go to a 2012 NC post on Snow Fleas: https://naturallycuriouswithmaryholland.wordpress.com/2012/03/09/snow-flea-mystery-appendage/) (Photo: Snow Fleas clustered in the track of a Black Bear that recently emerged from hibernation)
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Most adult spiders (as many as 85% of temperate zone species) are dormant during the winter, seeking shelter beneath the leaf litter. Their metabolism slows and their need for food is greatly reduced. Other species die at the end of the summer, and their eggs overwinter, protected inside silken sacs. A third, even smaller, group of spiders remains active through the winter.
Spiders’ body temperatures vary significantly, heavily influenced by their environment. Many spiders that remain active year round seek shelter in the subnivean layer between the ground and snow, where the temperature (+/-32°F.) is often warmer than the air. Occasionally, however, they do appear on the surface of the snow, where they are exposed to the wintery blasts of cold air.
Scientists don’t know exactly how these active spiders survive the cold. Some species can tolerate temperatures as low as -4° F.°. Glycerol acts as a type of anti-freeze for these arachnids, but its effect is marginal. In order to survive, some species bask in the sun and derive energy from their diet of snow fleas (a type of springtail) and other small prey, but these strategies don’t totally explain their ability to survive a New England winter. Species of spiders in the families Linyphiidae and Tetragnathidae (see photo) are often what you see crawling on top of the snow.
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Snow fleas, a species of springtail, are not a type of flea. Neither are they insects, though they are close relatives. During most of the year they live in the soil and leaf litter, consuming fungi and decaying vegetation. On warm winter days they appear on the surface of the snow, and are often described as “pepper on snow” due to their black color and tiny size (1 – 2 millimeters long).
Although they lack wings, they have two tail-like spring projections, or furcula, which are held like a spring against the bottom of their abdomen by a kind of latch. When the snow flea wants to move, the furcula springs downward, catapulting the snowflea as far as 100 times its body length. Snowfleas in the genus Hypogastrura possess three pinkish anal sacs which are usually located inside the snowflea, hidden from view. Just before jumping the snowflea everts these sacs from its anus. Their function has not been confirmed, but many biologists believe they serve as a sticky safety bag which prevents the snowflea from bouncing around when it lands.
Ground beetles (family Carabidae) are fast moving beetles, many of which are predators with specialized diets. One ground beetle (Cychrus caraboides) eats only snails (its head and thorax are very slender, allowing access to the inside of a snail’s shell). Another, Harpalus rufipes, limits its diet to strawberry seeds. Loricera pilicornis uses bristles on its antennae to trap springtails and mites.
The Bronze Carabid, Carabus nemoralis, (pictured) uses its large curved mandibles to crush and slice through prey – it will eat or try to eat just about any invertebrate, but specializes in capturing and eating slugs. Its hardened forewings, or elytra, have a coppery sheen to them, and parts of its thorax and the edges of its elytra are iridescent purple. This nocturnal, introduced, flightless, one-inch-long beetle resides throughout the Northeast and is already actively pursuing slugs.
One rarely even thinks about snowfleas (a species of springtail, Hypogastrura nivicola) until snow falls and then starts to melt. This is when these tiny wingless arthropods that catapult themselves through the air with the aid of a fork-like structure, or furcular, seem to magically appear out of nowhere. They actually are present year round, but their dark color makes them visible against the white snow.
The great majority of snowfleas live in soil, feeding on fungi, algae, decaying plant matter and bacteria. They work their way to the surface of the snow, crawling up the trunks of trees, plant stems and side of rocks where an open channel allows their migration. Thousands can be found on melting snow, especially in tracks or other depressions. No-one is absolutely sure of why they exhibit this behavior, though some scientists feel that these migrations are triggered by overcrowding and lack of food. Eventually those that survive on top of the snow make a return trip down into the soil.
Formerly classified as insects, snowfleas are now categorized as hexapods, due to some features they have which insects do not.