The visually controlled prey-capture behaviour of the European mantispid Mantispa styriaca.

Mantispids (Mantispa styriaca) are predatory insects; on bright sunny days, they wait in ambush for insect prey. The prey is captured as soon as it is within reach by means of lightning-speed strikes with the powerful forelegs. The strikes can take less than 60 ms. The mantispid accomplishes this almost as effectively as the larger praying mantis, which occupies a similar habitat, even though the praying mantis has apposition eyes with a high-resolution fovea, whereas the mantispid has unspecialized optical superposition eyes. Mantispa styriaca reacts to an item of prey when the latter covers a critical visual angle. The detection of prey immediately triggers adjustment reactions in the mantispid, which attempts to position the prey item in the visual field of both eyes and in the capture zone. Irrespective of the size of the prey, the capture reaction of the mantispid is always triggered if the distance to the prey falls below a certain critical value. As indicated by the analysis of individual video frames, immediately before an aimed strike, the item of prey is always positioned exactly in the centre of the binocular field of vision in the extended midsagittal plane of the mantispid's head. The strike may be triggered by the ommatidia of the left and right eyes, the lines of sight of which converge precisely on this region. The principal conclusion to be drawn is that the prey-capture behaviour of the mantispid appears to be based on a triangulation mechanism.