Keeping things simple is never easy in the real world, and for scientists who want to understand how Cataglyphis desert ants exploit their arsenal of navigation tools as they find their way home, it is almost impossible to control every feature of the environment while recording the insects’ footwork as they scamper across the desert. Although spherical treadmills, which can track animals’ helter-skelter movements, have been available since the late 1960s, none was nimble enough to record every fleet-footed detail of an ant's home run until Matthias Wittlinger, from the University of Freiburg, Germany, teamed up with Hansjürgen Dahmen and Hanspeter Mallot, at the University of Tübingen, Germany, to update the equipment. Redesigning the treadmill with a lightweight hollow Styrofoam ball – suspended on an airbed – that could be manoeuvred by the leggy insects with ease, while tracking the sphere's responses with modified optical mouse sensors, Dahmen was able to successfully track each twist and turn as ants attempted to find their way home.
However, Wittlinger, Verena Wahl and Sarah Pfeffer needed convincing that ants perched on top of the frictionless sphere were homing as naturally as if they were scurrying across the desert. Relocating the portable treadmill to Tunisia – complete with battery-operated air pump, plastic bottle air reservoir and laptop – Wittlinger, Wahl and Pfeffer trapped ants that had successfully located a feeder stocked with biscuit crumbs in the desert, swiftly attached a pin to each insect's back and tethered it on the treadmill sphere before recording the ant's route home. The ants soldiered directly to the location where they expected to find the nest, before slowing and beginning a meandering search for their missing home. Impressively, the treadmill successfully recorded the minute step-size difference between the outer and inner legs as the ant scoured the surface of the treadmill for its misplaced nest. And when the trio tricked the ants’ navigational compass by rotating the treadmill through 90 deg – in an attempt to send the ants off at a tangent – the insects obliged by switching direction according to the now-shifted position of the sun.
‘The possibility to investigate the orientation behaviour of animals mounted on top of the sphere… allows us to analyse complex behaviour in great detail’, says Wittlinger, who is keen to begin altering the ants’ surroundings to learn more about their homing strategy.