Ants use botanical knowledge when foraging

A recently published experiment that ants don't merely react to plant scents. They learn which scents are associated with food.

“Are ants botanists?” ask Annika Nelson and colleagues in a new paper. It’s an interesting question because they’re not merely asking if ants hang around plants. They’re asking if ants learn about plants.

Image: Canva.

The authors say that learning itself is not unusual in animals. However, most of these experiments happen in a lab. They wanted to know if it also happened in the wild, where it could make an ecological difference.

The experiment they did to find out was simple and elegant.

They tracked down ants in the wild and trained them to run to bait for food. Along the way the track had the scent of either Helianthella quinquenervis or Ligusticum porteri. After training the ants, they were let loose in a Y-shaped channel. The upright was scentless, but at the fork, they had a choice. One arm was scented with H. quinquenervis, the other with L. porteri. At the end of both arms was a bait. So the only difference was the scent.

If the ants had marched to the H. quinquenervis track, then all that would show would be that ants like H. quinquenervis. Likewise, the same was true for the L. porteri track. But because the ants had been trained with either one or the other plant, there was potentially a difference. That’s what they found. The ants trained on H. quinquenervis preferred the H. quinquenervis track. The ants trained on L. porteri, in contrast, preferred the L. porteri. There was no inherent difference, other then what they had learned.

There were some surprises. The authors wrote: “There was a significant difference in learning across years (all ant species combined in 2017 and 2018) with respect to the two plant species, with associative learning being stronger for H. quinquenervis in 2017 but stronger for L. porteri in 2018. This bias in associative learning might have been a result of the ambient resource environment within which the experiment was embedded.” They add in their discussion that while they were testing for scent, ants could be learning from local topography too. They suggest further experiments to see how the ants are learning.

They’re likely to be experiments worth doing. They conclude: “[A]nt associative learning of plant chemicals may occur in many contexts… and mediate ant population- and community-level effects on plants and the multi-trophic communities in which they are embedded… As a result, ant associative learning likely has far-reaching yet unrecognised effects on plant and insect evolutionary dynamics and community structure.” If ants are learning by association, then that will have consequences for plant and insect conservation when organisms are transplanted to conserve them.

Further reading

Nelson, A. S., Zapata, G. D., Sentner, K. T., & Mooney, K. A. (2019). Are ants botanists? Ant associative learning of plant chemicals mediates foraging for carbohydrates. Ecological Entomology. https://doi.org/10.1111/een.12794