Jumping spiders are famed for having up to four pairs of eyes. Together, the eyes comprise a modular visual system that gives the spider a good view of the world. But how does each pair of eyes contribute to the arthropod's vision? Explaining that the second pair of eyes (anterior lateral eyes) flank the central pair, Daniel Zurek and his colleagues from Macquarie University, Australia, wondered whether Servaea vestita spiders use the second pair of eyes to identify movement in the environment and to decide whether or not to orient towards it (p. ).
Covering four of the spiders' eyes with removable silicone blinds, the team showed them tethered live flies and movies of moving dots and tested the partially sighted arthropods' responses to the movements. The team also compared the responses of fully fed and hungry females with those of fully fed and hungry males, to see whether hunger motivated the spiders to orient in the direction of passing potential meals.
Analysing the partially sighted arthropods' responses, the team found that they could stalk and attack flies using their anterior lateral eyes alone. The spiders also oriented in the direction of fly sized dots moving at a walking pace, but ignored large fast dots that could have been hungry predators and small slow dots that resembled insects that were too small for the arthropods to eat. And when the team compared the males' and females' responses, the females were far more motivated to orient than the males, probably because their energy demands are higher.
Zurek says, ‘Even when the spiders were confined to visual input from this secondary pair of eyes, they could respond to targets that are very hard for other animals to see, and were able to detect, stalk and attack flies, which was unexpected.’
