Photo by Mark W. Moffet
Seeing all the available houses in the neighborhood and then choosing is not necessarily the best option, at least if you’re an ant. These house-hunting rock ants manage to make a decision together even without going through the options they have.
In this recent study conducted by Dr Elva Robinson and colleagues from the Bristol University, they put tiny radio-frequency identification tags on the ants; each of these small tags was about “1/2000” as big as a postage stamp. What they wanted to observe was how they made the difference between a poor house nearby and a better house further away. They were pretty surprised to find out the ants have a pretty sophisticated way of choosing, and location isn’t all that matters.
When a colony of ants decides there’s a need for a new nest, they first send out scouts to smell out the nearby nests. If the scout fancies the respective site, he, as an informed ant, briefs some other greenhorn. Then this greenhorn goes to the site and if he thinks it’s all good, he goes out to another and so on, until they reach a certain number. When they reach a quorum, they start moving the necessary materials for a new nest. This may result in a temporary split of the ant population, as some may pick a different place than the majority, or they can split into more than 2 places.
In the Bristol experiment, very few ants made actual direct comparisons between different options. They discovered that they choose the better place even if it’s location is 9 times further away.
Dr Robinson said:
“Each ant appears to have its own ‘threshold of acceptability’ against which to judge a nest individually. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies ended up in the good nest. Individual ants did not need to comparatively evaluate both nests in order for the entire colony to make the correct decision.
“On the other hand, animals – including humans – who use comparative evaluation frequently make ‘irrational’ decisions, due to the context in which options are compared or by inconsistently ranking pairs of options, (for example option A preferred to B, B preferred to C but C preferred to A).
“The ants’ threshold rule makes an absolute assessment of nest quality that is not subject to these risks, and circumvents the necessity for memorization and comparison of every site visited. Thus, simple individual behaviour substitutes for direct comparison, facilitating effective choice between nest sites for the colony as a whole.”
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