Measurement of lift and drag forces in the m N range experienced by benthic arthropods at flow velocities below 1.2 m s−1

SUMMARY. 1. A flow tank was constructed which generates homogeneous and stable flow of water up lo velocities of 1.2 m s−1. 2 A sensitive, two-component balance with its platform inserted in the bottom of the flume allowed the measurement of drag and lift forces in the mN range. 3 The drag forces experienced by several benthic arthropods, which cling to the roughened surface of the platform, are proportional to the square of the flow velocity. 4 Large biological variations in lift forces, leading even to negative lifts in some cases, are indications of special adaptations of the animals to counter the danger of being swept away from their support.