Ant intelligence; colony 'memory' (Introduction)

by David Turell , Tuesday, December 11, 2018, 15:30 (2174 days ago) @ dhw

Ants have individual memories, but the colony has a form of memory:

https://aeon.co/ideas/an-ant-colony-has-memories-that-its-individual-members-dont-have?...

"Past events can alter the behaviour of both individual ants and ant colonies. Individual carpenter ants offered a sugar treat remembered its location for a few minutes; they were likely to return to where the food had been. Another species, the Sahara Desert ant, meanders around the barren desert, searching for food. It appears that an ant of this species can remember how far it walked, or how many steps it took, since the last time it was at the nest.

"A red wood ant colony remembers its trail system leading to the same trees, year after year, although no single ant does. In the forests of Europe, they forage in high trees to feed on the excretions of aphids that in turn feed on the tree. Their nests are enormous mounds of pine needles situated in the same place for decades, occupied by many generations of colonies. Each ant tends to take the same trail day after day to the same tree. During the long winter, the ants huddle together under the snow. The Finnish myrmecologist Rainer Rosengren showed that when the ants emerge in the spring, an older ant goes out with a young one along the older ant’s habitual trail. The older ant dies and the younger ant adopts that trail as its own, thus leading the colony to remember, or reproduce, the previous year’s trails.

"Foraging in a harvester ant colony requires some individual ant memory. The ants search for scattered seeds and do not use pheromone signals; if an ant finds a seed, there is no point recruiting others because there are not likely to be other seeds nearby. The foragers travel a trail that can extend up to 20 metres from the nest. Each ant leaves the trail and goes off on its own to search for food. It searches until it finds a seed, then goes back to the trail, maybe using the angle of the sunlight as a guide, to return to the nest, following the stream of outgoing foragers. Once back at the nest, a forager drops off its seed, and is stimulated to leave the nest by the rate at which it meets other foragers returning with food. On its next trip, it leaves the trail at about the same place to search again.

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"Ants use the rate at which they meet and smell other ants, or the chemicals deposited by other ants, to decide what to do next.

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"It is likely that colony behaviour matures because colony size changes the rates of interaction among ants. In an older, larger colony, each ant has more ants to meet than in a younger, smaller one, and the outcome is a more stable dynamic. Perhaps colonies remember a past disturbance because it shifted the location of ants, leading to new patterns of interaction, which might even reinforce the new behaviour overnight while the colony is inactive."

Comment: Colony memory is passed from an older generation to the younger one. Individual ants show some memory ability.