Picture of the Day

Footprints In Water

This image shows small water creatures (Daphnia lumholtzi), 1.5 millimeters in total length, that create relatively large disturbances in their surrounding water. Each animal swims somewhat differently, and, being of different sizes and shapes, creates species-specific disturbances similar to terrestrial animals moving in snow. Optical techniques allow visualization of these "footprints." The creatures use these footprints to distinguish between predators, prey and mates. The Daphnia seen here moved from the left lower edge to the center of the picture, filtered a volume of water there in search of food, then changed position to start filtering a new volume of water. The image was taken during research by Professor J. Rudi Strickler, currently of the University of Wisconsin-Milwaukee.

Visit Website | Image credit: J. Rudi Strickler, University of Wisconsin-Milwaukee