Anterior lateral eyes ofLycosa tarantula(Araneae: Lycosidae) are used during orientation to detect changes in the visual structure of the substratum

Previous studies in the wolf spider Lycosa tarantula (Linnaeus 1758) have shown that homing is carried out by path integration and that, in the absence of information relative to the sun's position or any pattern of polarized light, L. tarantula obtains information as to the angle it must turn to home through the anterior lateral eyes (ALEs). In the present study, spiders were trained to walk over a black-and-white grating and afterwards tested either over a white substratum, the same substratum used for training or the same substratum rotated 90 deg (two groups: ALEs covered and only ALEs uncovered; they were tested first without their eyes covered and then with their eyes covered). The directional bearing was measured both in training and test conditions. Under the white or the same substratum in test conditions, the directional bearing had the same mean direction and a distribution similar to that of the training sessions. When the substratum was rotated 90 deg, the directional bearing had the same mean direction but the distribution was significantly different from that of the training sessions. Moreover, if ALEs were covered, spiders behaved as if the substratum had not been rotated and the directional bearing distribution was similar to that of the training sessions. But, if ALEs were the only eyes uncovered, spiders behaved as if no eyes were covered and directional bearing distribution was similar to that of the test condition. It is suggested that, when homing, L. tarantula uses both idiothetic information and visual information gathered through ALEs. These findings present the first evidence that spiders can use the visual structure of the substratum to return home.