Navigation and behaviour of four Collembola species migrating on the snow surface

Abstract

In Norway, four species of Collembola, Hypogastrura socialis, Vertagopus westerlundi, Isotoma hiemalis and I. violacea, are regularly active on the snow surface during mild weather. In all species, each individual jumps in a rather straight line, using the sun as a “compass”. If the sun's position was turned 180° using a mirror, the animal also turned 180°. As the sun does not have to be directly visible, the animals probably can use polarized light as well. Different individuals often migrate in quite different directions. At least three of the four species live in patchy and temporary habitats, and sooner or later have to find new patches. Winter migration on the smooth and moist snow surface is their only possibility to move over great distances. Before each jump, the collembolan orientates its body relative to the sun either by rotating horizontally on the spot or by walking a little in a crooked line. H. socialis lands with extended anal sacks, which adhere the animal to the snow surface and enable it to position itself rapidly again. Even in overcast weather, collembolans sometimes show a more or less directional movement. An experiment indicated that navigation under such conditions was by means of light and dark elements in the surroundings.