October 21, 2013 | 2
Think about where you’ve been today, and how you found your way there. As humans, we use different navigational techniques at different times. You can probably think of some times that that you’ve relied more on heading in a particular direction, knowing roughly where a place is that you’re trying to get to (like ‘north’ or ‘up hill’). At other times, you may have relied more on particular landmarks (‘I know I need to turn right at the bookshop’). You may have even used more unusual cues, such as locating a pizza restaurant on a busy street by a good smell wafting from it.
Other animals aside from humans use a variety of techniques to find their way around. Some of the more interesting ones include sea turtles, that can navigate using the earth’s magnetic fields, and pigeons that will actually follow railways and roads, including flying ‘around roundabouts’.
Just like with humans though, other animals also use different ways of navigating at different times. Ants are amazing navigators, having a bunch of different strategies in their ‘navigational toolkit’. The first is called ‘path integration’, a method that humans apparently have too (although I sometimes question whether I have it). An individual can wander (say, from their nest) and keep track of the distance and direction they are going in. They might meander all over the place before they find what they’re looking for (say, some food) but then on their return home they walk the shortest route in a straight line. Ants can also learn scenery, like what the objects along the horizon look like, so they can tell which direction they should be heading in. Finally, if both of these systems fail and the ant is lost, it then carries out a systematic search of the area, consisting of gradually extending loops until they find their home or recognise a landmark.
A recent study has found that, in addition to these navigational tools, ants can also employ another strategy: backtracking their steps when they get lost. To find this out, the researchers tested desert ants near Alice Springs, Australia. They left bits of cookie (ant food) by the nest. When an ant went to retrieve it, the researchers let her pick it up and bring it almost all the way back to the nest, but then caught her in a tube and moved her to a different location. The ant was now lost, but could use its celestial compass (where the sun is in the sky) to know roughly what direction to walk in.
Testing a total of 730 ants, the researchers found that when the ants suddenly found themselves in unfamiliar terrain, they didn’t carry on walking in the same compass direction they had been walking before, but instead walked in the opposite direction: they backtracked their steps.
Interestingly, the ants don’t seem to backtrack their steps if they are re-located by the researcher before they can see their nest vicinity (being more than 2 metres away). They need to have the impression that ‘hey, I swear my nest was just in front of me a second ago’ to then backtrack their steps.
When might ants use backtracking in their day to day life? Ants, being so small and light, are often displaced by a swift gust of wind, which could put them metres away from their previous position. They might also just use backtracking if they get lost using their other navigational tools, especially on their first few foraging expeditions out of the nest.
Maze: Jon Candy
Ants: Antoine Wystrach and Sebastian Schwarz
Wystrach A, Schwarz S,Baniel A, Cheng K. 2013 Backtracking behaviour in lost ants: an additional strategy in their navigational toolkit. Proc R Soc B 280:20131677.