Ants may be smarter than we give them credit for. Tool use is seen as something brainy primates and birds do, but even the humble ant can choose the right tool for the job.
István Maák at the University of Szeged in Hungary and his team offered two species of funnel ants liquids containing water and honey along with a range of tools that might help them carry this food to their nests.
The ants experimented with the tools and chose those that were easiest to handle and could soak up plenty of liquid, such as bits of sponge or paper, despite them not being found in the insects’ natural environment.
This suggests that ants can take into account the properties of both the tool and the liquid they are transporting. It also indicates they can learn to use new tools – even without big brains.
Some ant species are known to use tools, such as mud or sand grains, to collect and transport liquid to their nests. But this is the first time they are shown to select the most suitable ones, says team member Patrizia d’Ettorre from the University of Paris-North, France.
To investigate this behaviour, the team offered Aphaenogaster subterranea and A. senilis ants various possible tools, both natural, such as twigs, pine needles and soil grains, and artificial.
The ants experimented with the tools and eventually showed preference for certain tools – even unfamiliar ones. The ants would drop the tool into the liquid, pick it up and then carry it to the workers back in the nest to drink from.
Subterranea workers preferred small soil grains to transfer diluted honey, and sponge for pure honey. Most of them even tore the sponge into smaller bits, presumably for better handling.
Senilis started off using all the tools equally, but then focused on pieces of paper and sponge, which could soak up most of the diluted honey they were offered. This indicates that they can learn as they go along.
Factors such as the weight of the tools could also have influenced the ants’ choice, but the researchers believe the tools’ absorbency and ease of handling mattered the most.
Stuck for space
Aphaenogaster ants possibly developed such tool use because, unlike many other ants, they can’t expand their stomach, says d’Ettorre. “They had to find a way to exploit the valuable resource of liquid food.”
This way, when ants come across a fallen fruit or a dead insect in the wild, their fluids can be transferred to the nest for the rest of the colony.
As ants live in a highly competitive environment, natural selection may favour using such tools to help feed the colony, says Valerie S. Banschbach at Roanoke College, Virginia.
And these ants may have been happy to try novel materials because which particular tools are available in their natural habitat varies according to the season.
“Many other accomplishments of these small-brained creatures rival those of humans or even surpass them, such as farming fungi species or using ‘dead reckoning’, a sophisticated navigation to find their way back to the nest,” says Banschbach. “The size of brain needed for specific cognitive tasks is not clear.”
“Tool use in insects is largely genetically controlled and evolved from selection of advantageous genetic mutations,” says Gavin R. Hunt at the University of Auckland, New Zealand. This is unlike most tool use in birds or primates, which begins as novel behaviour and can sometimes be enhanced through genetic changes, he says.
Journal reference: Animal Behaviour, DOI: 10.1016/j.anbehav.2016.11.005