A Technique for Observing the Behaviour of Small Animals Under Field Conditions

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