Researchers wanted to discover which group decision-making strategy weaver ants used when transporting their prey back to the nest.
Introduction
Animals that live in groups need to be great at problem-solving and working as a team. They must have consensus to avoid conflict and keep the group together. There are two ways to achieve consensus:
“Follow the leader” – one or a few individuals have control over the group’s decisions.
“Wisdom of the crowd” – the group makes a decision by bringing together all the members’ opinions.
An example of when groups need consensus is during cooperative transport. This is when several individuals work together to move a large object from A to B. This is only really seen in ants and humans. We can simply talk to each other, but it’s not quite that easy for ants. They can only rely on local information gathered from their environments. We have seen evidence of cooperative transport in over 40 ant species from all over the world. It helps ants retrieve much larger items of prey, allowing them to feed the colony.
We examined the cooperative transport behaviour of weaver ants (Oecophylla smaragdina). Weaver ants can forage for large prey items through cooperative transport. They have even carried birds back to their nests! But we wanted to know how they are so successful. Do they “follow the leader” or use the “wisdom of the crowd”?
Methods
To help answer our question, we observed weaver ants carrying objects in the laboratory. We used more than 2,000 ants from nine queenright colonies in our experiments. We released the ants into a large arena. We hadn’t given them any food for 24 hours to make sure they were hungry.
We put grasshoppers in the arena for the ants to transport. They were cut into pieces to represent light, medium, and heavy items. We tied the grasshopper pieces to the floor of the arena with a thin string, one piece at a time. The string stopped the ants from bringing the grasshoppers all the way to the nest. But it still allowed the group to swing from side to side (Fig. 1). We recorded the ants’ behavior once the ants picked up the grasshopper piece and fully extended the string. We looked at the size of the group and how far they moved away from the average direction of travel.
We also wanted to know what would happen when ants could move freely in a complex environment. So we set up a corridor at a right angle to the arena entrance. Then we placed a grasshopper piece in the middle of the corridor for the ants to find and transport. We recorded the ants’ behavior again. This time we looked at how fast the ants moved and how often they stopped. We also looked at how straight their path was and whether they ever retraced their path.
Results
We found that the heavier the piece of grasshopper, the larger the group of ants that transported it. Also, the heavier the piece was, the less side-to-side movement the group had. The groups that carried the lightest grasshopper pieces moved the farthest from their average direction of travel. So, as the groups got bigger, their paths became straighter. This matches what we would expect from the “wisdom of the crowd” strategy.
When we made the environment more complex, we saw similar results. Ants moved more slowly within the corridor than the rest of the arena (Fig. 2). When ants carried lighter grasshopper pieces, they stopped less. They also stopped less when they were in the open arena, no matter how heavy the piece of grasshopper.
Discussion
We found that weaver ants work together to navigate accurately while transporting heavy objects. We saw that their path gets straighter with more ants helping. This shows that they use the “wisdom of the crowd” strategy. Each ant has their own sensory mechanism telling them where they should be going. They pool together their information to increase their accuracy. They are able to sense the forces produced by the other ants through the object they are carrying. As the group size increases, the accuracy increases. If individual ants make errors in the direction they pull, it gets canceled out. This means that larger groups end up taking more direct routes.
We confirmed this by looking at how weaver ants navigated when they could move freely within the environment. They slowed down and stopped more when they were in the corridor. This is because they had more conflicting ideas about which direction to travel. When the group made it to the open arena they were able to speed up. This is because more individuals agreed with each other. In contrast, ants that “follow the leader” don’t slow down or stop more in similar experiments. They just follow the leader!
What makes weaver ants so special? They live in complex habitats and likely have knowledge of the route back to their nest. They use visual, magnetic, and olfactory cues to help them navigate. This then allows them to contribute their information to the effort of the group.
Conclusion
You can do things with a team that you might not be able to do by yourself. Just like weaver ants! There are also lots of different ways to work with a team. Think about how teamwork plays a role in your own life. It might be at home or at school. How do you communicate with those around you? Does it vary depending on the environment you’re in? Or on the number of participants? When do you tend to follow a leader (or be the leader!) and when do you cooperate to make decisions?
