When a forager ant sets out on her mission she's got three goals in mind;get food, do it quickly and don't die. According to father-and-son team,Thomas and Matthew Collett, ants rely on three navigation strategies for efficient foraging. First they keep a record of the route they travelled from the nest to a tasty treat, quickly calculating the most direct route when they return home. The ants also remember the size and location of the surrounding landmarks and use them to refine their trajectories. The third strategy only comes into effect as an ant becomes familiar with a route. Matthew Collett explains that if a route is composed of several sections, ants learn the direction and distance that they must go along each section to reach their goal. According to Collett, ants were already known to use this type of memory while homing, but it wasn't clear whether ants used it to return to a feeding site (p. 895).
Travelling to Tunisia, the duo set Cataglyphis fortis a navigation challenge. Clearing the barren landscape of vegetation around the nest, the Colletts surrounded the nest with an enclosure, which had one exit into a 10 m long channel. Placing a small tray between the exit and channel, the pair trained the ants to scamper across the tray and along the channel for 6 m before they took a sharp 90 deg. turn toward a feeder 6 m to the west. Once the ants had learned the route after leaving the channel, the Colletts tried foxing them by carefully carrying the ants on the tray and putting them down a few metres further along the channel. If the ants were undisturbed by their tray flight and they were using their route memories, they would carry on making their 90 deg. turn after leaving the channel, and head out to where the feeder should be: which is what they did. The ants appeared to be using a route memory.
But when the duo got down to the ants' level, they realised that the insects may still have been able to see two bushes 30 m away on their horizon. The crafty insects could still be using them to navigate by, so the Colletts grubbed the bushes up and retested the ants' accuracy.
Initially everything was fine. During the first day the ants turned successfully, after scampering along the channel, and headed west for 6 m. They were clearly using their memory of the direction and length of the route's final section. However, by the following day, many of the ants were losing their way, and the situation did not improve. They seemed to have lost their navigation memory. Matthew Collett remembers that it was immediately obvious that it had something to do with the grubbed up bushes. Maybe the landmarks were essential for the insects to retain their memory.
Placing two plastic tubes on the ground where the bushes had stood, the father–son team was delighted to see that the ants soon recovered their ability to locate the feeder. The landmarks were essential for the insects to both learn and hold on to their route memory. So ants are capable of learning familiar routes but they need some local landmarks to retain the memory.
