Water striders’ ability to walk and jump on water surfaces has long inspired robot designers who want to mimic the insects’ talent. Now, scientists from the State Key Laboratory of Tribology at Tsinghua University in China have measured for the first time key parameters that allow them to walk on water - by studying their leg shadows. The findings could contribute to designs for water-skimming robots. The researchers placed a white sheet of paper at the bottom of a lab aquarium housing water striders and installed a light source above the water. The insects’ straight legs cast shadows that were rounded, representing the curvature of the water and the expelled water volume from which the floating force and weight can be calculated. From these measurements, the striders’ slightest shifts in weight and body angle could be detected for the first time.