Light thresholds for colour vision in workers of the ant Myrmica sabuleti (Hymenoptera, Formicidae)

Previous Studies suggested that workers of the ant species Myrmica sabuleti have different light thresholds for distinguishing different colours. Here we assess these thresholds and find that the light thresholds required to distinguish colours from grey are lower than those necessary to discriminate between two colours. The two thresholds are somewhat lower for ants trained under low versus high light intensity. In every case, the ants' threshold decreases from red to violet. All these thresholds are lower than those. required for perceiving shapes. The visual system of workers of M sabuleti under very low light intensity may thus consist of discriminating only coloured spots from grey and under slightly higher light intensity, differently coloured elements where the eyes are used in superposition mode Under high light intensity, these ants see (although not sharply) shapes and lilies, using their eyes in apposition mode. Moreover, workers of this species demonstrated their best colour discrimination in seeing the colours yellow and blue tinder high light intensity, and green and violet tinder low light intensity. Therefore, these ants' visual system may be adapted to the quantitative and qualitative variations in natural light during the day