Abstract
Small animals are difficult to observe under field conditions, and arthropods of less than 10 mm body length are particularly difficult subjects. When such animals are making complex movemerits with small parts of their body (mouth parts, reproductive organs) some device is needed to augment direct vision. One solution to the problem is to use the zoom optics of a movie camera equipped with close-up devices (Robinson & Robinson, 1972). Recently, however, one of us (M.H.R.) studied the behaviour of Drosophila-sized flies that associate with orb-web spiders and spend long periods standing on the spider’s body. To find out what the flies were doing there it was essential to see them in close-up and be able to watch them, for long periods, under field conditions. Watching them through the macrosystem of a movie camera gave insufficient magnification. We solved the problem by adapting a stereo-binocular microscope for horizontal viewing. We feel that this adaptation has a wide variety of potential applications in field ethology. It may be a re-invention but is worth describing here.