March 18, 2012

the tiny snow flea


One of the reasons that winter is a fascinating time for us is the annual emergence of the snow flea. While they're one of the smallest of the creatures that inhabit Windward, they're one of the most important of the creatures we share this land with, both for what they do and for their role as an indicator of our soil's health.

The snow flea (Hypogastrura nivicola) gets its common name because of the way that it gathers in great numbers when the snow starts to melt in the early spring. It's a tiny hexapod that lives most of its solitary life underground, but it takes advantage of the melting snow to congregate in large numbers. The ducks especially enjoy the springtail's mating season, and they make a distinctive sound as they seine the water for them.

ducks busily grazing on snow fleas

Snow fleas are black and about the size of the letter "i" in your average book print, so an individual black snow flea isn't really noticeable even against a background of white snow. It's when they gather together by the thousands and float on puddles of icy snow-melt to mate that they catch the eye. It's sort of the hexapod version of Spring Break.

snow fleas forming a black scum
around the grass shoots

One reason they come out at this chilly time of year is that they have no breathing apparatus; instead, they absorb oxygen through their skins. If they came out at a time when there was less than 100% humidity, they would not only dehydrate, they would suffocate.

The freezing water actually enables them to be fully energized because the amount of oxygen that can dissolve in water is an inverse of its temperature; the colder the water, the higher its oxygen content. That's part of the reason that the frigid arctic waters are able to support such an abundance of life ranging from the tiny krill to the great whales.

The springtail is so named because it has a "tail" that lies cocked up under its belly. When on the surface and threatened in some way, it can release that tail in as little as 18 milliseconds and propel itself a couple of feet into the air.

The springtail plays a number of important roles in sustainable agriculture and sylvaculture especially. It spends most of its life burrowing through leaf litter breaking down the components and freeing them up for re-absorption by our forest and grasses. They're also the critters who haul around the spores of the mycorrhizal fungi that make up one of the most important strands in a forest's web of life. Springtails also help keep that web intact by consuming the spores of damping-off fungi that can kill newly sprouted seedlings.

Because of the way they absorb oxygen through their skins, springtails are highly susceptible to herbicides and one of the first casualties of modern farming techniques such as no-till farming with its heavy reliance on herbicides. The plentiful gatherings of springtails we see are visible confirmation of the health of our soil, and that brightens any day, even a gloomily wet day in early March.