Phenology Note: February 28, 2010 - Collembola

Although not considered species of special interest in the Eastern Pennsylvania Phenology Project, Collembola are a unique group of Arthropods that are a sign of warming temperatures signifying the coming of spring.  Collembola are generally 1-5 millimeters and most are very good jumpers.  For most of the winter, these insect-like hexapods live beneath the ground, in tree trunks, and under rocks.  During the summer, tend to live under leaf litter and just below the surface of the ground.  During the fall and winter, some Collembola move around (primarily by jumping) and can be incredibly numerous on the forest floor. 

One common Collembola that congregates like this are "snow fleas" which belong to the family Hypogastruridae.  Groups of hundreds often congregate on snow patches and puddles once the temperature is in the thirties.  The Hypogastruridae that often gather on top of the snow are like the ones pictured below.  Under magnification, they appear blueish with small hairs.  With the naked eye, these Collembola appear black or sometimes purple.  This particular group is easiest to find during late winter/early spring and late fall/early winter.  This time of year, the groups gather in sunny snow patches and puddles.

Hypogastrura sp. Snow Flea

Hypogastruta nivicola - Snow Flea

Although the Hypogastruridae are the most common Collembola this time of year, there are several other species present.  One interesting species is Hydroisotoma schaefferi.  This species was introduced from Europe and is now fairly common in puddles and springs from January to April.  These do not congregate like the previously mentioned species, they are often found in small groups in water.  This species often looks brownish-orange with a dark line down the back.

Hydroisotoma schaefferi - an introduced Collembola

A Collembola in the family Isotomidae surrounded by Hypogastrura.

There are many species of Collembola, many of which mark the arrival of spring by becoming more abundant and more evident.  When the ice starts melting and puddles begin forming, be sure to look for these extremely small creatures while exploring the woods.

Photos: Corey Husic