If a person were far from her desert camp, she probably wouldn’t try to sniff her way back. For some ants, however, smelling their way home makes perfect sense. Cataglyphis fortis travels tortuous routes up to 100 meters from its nest in search of food, dead arthropods, in Tunisia’s inhospitable salt pans.
Most ants leave behind a pheromone trail when they go out to collect food. But the desert heat would destroy such a path. So, researchers assumed that C. fortis used visual cues to get back to its nest.
But German researchers discovered that desert microhabitats have unique odors that may guide the ants home. While the flat salt pans might appear homogenous, a closer look reveals that the continuous salt crust is occasionally interrupted by cracks, as well as pieces of wood and plants (remnants of past flooding). Using gas chromatography, the scientists determined that these structures give off different odors, possibly providing ants with “olfactory landmarks” to help them navigate. The study is published in Frontiers in Zoology.
The ants do rely on vision, too: Once the insects get close to the nest, they look for landmarks to help them pinpoint the entrance.
To test the ants’ ability to use olfactory info for homing, the researchers conducted field experiments to train the insects to recognize an odor, indole, which marked a hidden nest entrance. It worked. Ants learned to associate the nest entrance with a specific odor, and they even picked out that odor from a blend of four scents.
(It’s obviously not the same because I rely on visual landmarks, but this has me thinking back on my morning run: I set out going north, past the bodega that always has the aroma of bacon around it, and veered east about the time I hit the sketchy garage that smells like oil. I rounded my way south between the cemetery and the place where the subway garbage trains empty their loads—even in winter there’s a slight reek of decaying trash. I knew I was nearly home when my nose picked up the buttery, yeasty scents emanating from the bakery a couple of blocks from my apartment. Thank goodness home is marked by the scent of baking bread, and not the stench of garbage.)