Tenebrio larvae show a negative phototactic reaction; this is an easily provoked response. Simple manipulations allow a satisfactory amount of data to be collected in a short time Comparison of the results of two tests shows that larvae can evaluate different intensity of stimuli, and react accordingly. This is a good opportunity to Introduce polar co-ordinates and the peculiarities and exigencies of circular data. © 1994, Taylor & Francis Group, LLC. All rights reserved.