A saline drone was a miniature robot that absorbed moisture, preferably ionic compounds, from other creatures and used them to replenish its host. They looked like flying, blinking lights.
Saline drones, which River Song speculated had fallen to Earth from a passing starliner, attacked Daphne Garsington in a Mesopotamian tomb in the 1920s and drained her of all her bodily fluids. River Song and Bertie Potts later entered the tomb and escaped the drones. (AUDIO: The Boundless Sea)