As a child I used to spend hours watching groups of ants move large objects and wonder how they managed to coordinate themselves. If I had to move some furniture with some friends, I’m sure we’d be talking the whole time about which way we were going and how fast, but as far as I could see the ants weren’t doing any talking. This is a question I never found the answer to, so I was delighted to hear a talk recently by Helen McCreery at the Animal Behaviour Society conference on how ants cooperatively transport objects.
If ants find something they want to take back to their nest, say a nice big dead cricket, you might think that the easiest way to do this would be for each ant to chew off a little bit of cricket and carry its own piece back to the nest. A lot of species of ants do indeed do this. In some cases, however, it might be better to get the whole object back to the nest as quickly as possible. Perhaps while the ants are all busy dismantling the insect to carry home other ants or animals might move in and take the dead cricket for themselves. To avoid this, some species of ants instead move the whole item back to the nest and dismantle it there.
Now, one of the things that’s pretty interesting here is that some species are much better than others at moving objects. As with humans, some removal companies can help you move your house with greater ease and efficiency. Long-horn crazy ants (not quite sure what these guys did to deserve this name) seem to be pretty good at moving things as a group. As you can see in this video here, they coordinate well together, moving quickly towards their home and manoeuvring around obstacles with relative ease.
However, for most other species like the mound ant, McCreery describes their behaviour more like a ‘tug of war’: some ants pull one way while others pull the other. But why are some ants the equivalent of the professional (most probably German) efficient removal company while others are more like asking a group of drunk friends to help you move? McCreery and Michael Breed are addressing just that question: what makes some species of ant so much more efficient than others at moving objects?
To try and answer this question, the researchers plan to look at a number of species that differ in how good they are at cooperating while moving objects. For now, McCreery has focused on the mound ant Formica podzolica. As the name suggests, this species builds large mounds where they nest. McCreery told me that if you stand too close to their mound (as scientists who spend a lot of time watching them tend to do), the ants swarm all over you. Scientists will often complain about these kinds of things, but I think they love it really.
To learn more about how these ants move objects together, McCreery gave the ants a bait to move together. The bait consisted of dead superworms. She observed that if the ants couldn’t move the bait in one direction, then they’d try moving it in another direction, or just give up. This led the researchers to hypothesize that the persistence of individual ants in moving an object in a particular direction might affect the overall efficiency of moving the object as a group. As with the human movers, if they persist in moving a sofa in different directions, then the sofa isn’t likely to move very far. However, if the individuals on one side of the sofa pulling in one direction are very persistent, while the ones on the other side are not, then the sofa will move more in one direction in a more efficient manner.
To see if the persistence of ants affects their efficiency at moving things, McCreery added a ‘fake’ ant to a group of ants doing the moving. This ‘fake’ ant was designed to be the most stubborn, persistent ant ever in existence. In order to work out how strong ants are, and so how much this fake ant should be pulling on the object the ants are trying to move, McCreery had ants pull a coiled up chain to see how much of it they could pull.
By recording several ants each pulling the chain, McCreery calculated that the average force that a single F. podzolica worker exerts is around 0.004 N. To make her fake ant exert this level of force, she let ants move an object attached to a string, and then pulled the string through a pulley system that exerted the force of one ant. She found that when she added just one fake ant, it didn’t seem to change the efficiency of the movers: they were just as efficient with or without the extra persistent fake ant added. However, when McCreery added two fake ants (twice the force) then the ants tended to be more direct in their movement, moving more in a single direction with less meandering, even though they didn't move any faster overall.
Carrying on from this work, the researchers are now looking at two other species of ants in addition to the mound ant. These three ant species vary in how efficient they are at moving objects, and the researchers are now looking to see if they also differ in how persistent they are. This work is ongoing, so watch this space to see what happens here!
Many thanks to Helen McCreery for discussing this research with me
Sofa moving: Fabricio Zuardi
All ant photos and videos: Helen McCreery