The properties of the visual system in the Australian desert ant Melophorus bagoti

The Australian desert ant Melophorus bagoti shows remarkable visual navigational skills relying on visual rather than on chemical cues during their foraging trips. M. bagoti ants travel individually through a visually cluttered environment guided by landmarks as well as by path integration. An examination of their visual system is hence of special interest and we address this here. Workers exhibit distinct size polymorphism and their eye and ocelli size increases with head size. The ants possess typical apposition eyes with about 420–590 ommatidia per eye, a horizontal visual field of approximately 150° and facet lens diameters between 8 and 19 μm, depending on body size, with frontal facets being largest. The average interommatidial angle Δϕ is 3.7°, the average acceptance angle of the rhabdom Δρrh is 2.9°, with average rhabdom diameter of 1.6 μm and the average lens blur at half-width Δρl is 2.3°. With a Δρrh/Δϕ ratio of much less than 2, the eyes undersample the visual scene but provide high contrast, and surprising detail of the landmark panorama that has been shown to be used for navigation. ► Compound eye and ocelli size increases with head size. ► Number of ommatidia ranges between 420 and 590 per compound eye. ► Horizontal visual field of approximately 150°. ► The average interommatidial angle of each compound eye is 3.7°. ► Compound eyes provide sufficient detail of landmark panorama for navigation.