In stimulus generalization, a subject that has learned to respond to one target stimulus also responds to other similar stimuli. Shepard's law of generalization states that probability of responding decreases exponentially with psychological distance between test and target stimuli (Shepard, R.N., 1987. Toward a universal law of generalization for psychological science. Science 237, 1317-1323). In experiments on spatial generalization, honeybees were trained to find a target at a location near one principal landmark, and then tested with the target at different locations. A theoretical scale of positional mismatch between test and target locations was computed by a weighted sum of discrepancies between test and target locations in the compass direction (0.25 weight) and size (angle) of projected retinal height (0.375 weight) and width (0.375 weight) of the landmark, derived from the model of Cartwright and Collett (Cartwright, B.A., Collett, T.S., 1982. How honeybees use landmarks to guide their return to a food source. Nature 295, 560-564; Cartwright, B.A., Collett, T.S., 1983. Landmark learning in bees. J. Comp. Physiol. A 151, 521-543) of landmark use in honeybees. Based on the theoretical scale, but not on physical distance, Shepard's law fit data from four experiments, the first time it has been confirmed in an invertebrate. Copyright (C) 1999 Elsevier Science B.V.