Mike wrote to the "Consult-Ant" with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.
6) So ants have pheromones they lay to provide trails to sources of food, but I've read somewhere that ants have memory. Can you explain more about that? A 'leader' ant would teach a 'follower' ant towards a food source. Is that true? with only certain species?
Although their brains are obviously very different from ours, we do have some evidence that worker ants do have memories. For example, James Hare and Thomas Eisner showed that workers ants that had been exposed to moth eggs (Utetheisa ornatrix) full of nasty alkaloids would still avoid moth eggs days later. But not just avoid toxic eggs. In an elegant study, Hare and Eisner were able to rear moths that did not contain the alkaloids, producing eggs that were perfectly edible. Ants with no previous exposure to the alkaloid-laden eggs would eat the alkaloid-free ones readily. It was the workers with previous experience (up to 33 days prior!) that would avoid both kinds of moth eggs.
In a paper in Myrmecological News, Dornhous and Franks give an overview of cognition in ants, and other insects. They report that foraging ants use memory to find food sources, and can even remember times of day the food sources are available. Ants can also remember where they have looked for new nests. Wood ants apparently memorize visual "snapshots" of landmarks as they travel about. Although chemical cues are important, if an ant is dropped into its environment in a place with no chemical trails, it might be able to orient back to the nest using visual cues. Ants have been known to be able to learn to move through mazes since Schneirla's work in the early 1940's, so are able to improve their performance of certain tasks.
Ant running a maze.
Dornhous and Franks point out that most of the studies of cognition in insects have been carried out with honey bees and fruit flies, for various reasons. There is still a lot of work to be done on ants.
As for the leader and follower ants, would you believe that ants could be teachers? When researchers looked at how ants lead their nest mates to new sources of food or a better nest, they found that the experienced ants actually taught the others where to find the target during a process known as “tandem-running.” Tandem running is when one ant follows another closely while running.
To discover whether or not the ants were actually teaching each other, first the investigators needed a solid definition of what it means to be a teacher. They decided that to be a true teacher, the ant must change its behavior when it encounters an inexperienced ant. At a cost to its own ability to perform the task, it must set an example so that the untrained ant can learn more quickly than it could have without training.
Sure enough, teacher ants approached uninformed nest mates and literally showed them the way to the food or new nest by running ahead. The follower gives feedback to the leader by continuous touching with her antennae. By teaching others the path to take, the teacher ant ran slower than it would have without a follower, but the pupil ant found the target in two-thirds the time it would have taken without help.
To learn more:
Dornhous, A. and N. R. Franks. (2008). Individual and collective cognition in ants and other insects (Hymenoptera: Formicidae). Myrmecological News. 11: 215-226.
Franks, N.R. and T. Richardson. (2006). Teaching in tandem-running ants. Nature. 439: 153.
Hare, J.F. and T. Eisner. (1993). Pyrrolizidine alkaloid deters ant predators of Utetheisia ornatrix eggs: effects of the alkaloid concentation, oxidation state, and prior exposure of ants to alkaloid-laden prey. Oecologia. 96: 9-18.
R. Josens, C. Eschbach, and M. Giurfa. (2009). Differential conditioning and long-term olfactory memory in individual Camponotus fellah ants. J. Exp. Biol. 212:1904-1911 Retrieved from http://jeb.biologists.org/cgi/content/abstract/212/12/1904
Nowbahari, E. (2007). Learning of colonial odor in the ant Cataglyphis niger (Hymenoptera; Formicidae). Learning & Behavior, 35: 87-94. Retrieved from http://lb.psychonomic-journals.org/content/35/2/87.abstract ( free .pdf available)
Y. Provecho and R. Josens. (2009).Olfactory memory established during trophallaxis affects food search behaviour in ants. Journal of Experimental Biology. 212: 3221-3227. Retrieved from http://jeb.biologists.org/cgi/content/abstract/212/20/3221 (.pdf available)
Schneirla, T.C. (1943). The nature of ant learning II. The intermediate stage of segmental maze adjustment. Journal of Comparative Psychology. 35: 149-176.