Leaf-cutter ants in South and Central America are the major herbivores in the environment. Their trails range for several hundred meters from their colony. Long lines of ants with shreds of leaves, sometimes up to four times the weight of their tiny bodies, march from the forest back to their subterranean nests. When these lines cross asphalt roads the stark green of the leaves is clearly visible against the black of the tarmac. But for a long time, myrmecologists could only guess what the leaf-cutters were doing with all that roughage. It was apparent that the ants did not eat the leaves because, when zoologists ran tests, the ants did not have the enzymes to break down many of the plants. The scientists then guessed that the ants were building their nests with the vegetation. But when they broke open nests, they could never find the postulated leafy bulwarks. And so the thousands of tons of leaves, which leaf-cutter ants carry into their nests annually, seemed to have just vanished. But this simply did not make sense. So a few researchers, curious at this magic trick, kept looking.
They observed ants in the field and they found something astounding. Inside every leaf-cutter ant nest, myrmecologists discovered chambers of fungi. The fungi are tended by pygmy ants. These pygmies––like coal men working in the depths of a 19th century steamer––take the leaves foraged by the larger terrestrial worker ants and pile them at the base of each fungus. The fungi in turn extract nutrients from the decomposing leafy material. They then use the nutrients from the process to make spores. The ants then, after feeding the fungi, collect the fungi’s spores, which they in turn eat. The ants are farmers. Thus by incorporating an alien species into their everyday feeding methods, leaf-cutter ants cull vital nutrients from previously unusable plants, thereby allowing them to harvest a smorgasbord of plants.
Such a discovery could only be made by close observation and long-term desire to answer the question, Where does all the roughage go? In this curriculum we will investigate how ants gather roughage, where it goes, and how that impacts their population.
We will begin with a simple model of just one ant. Click the "Open Introduction Model" button below to begin.
Red blocks are procedure names. They need to be connected to blue blocks, or commands, to work. Try connecting wander to move-ant in the white space, hit recompile, hit setup, and then hit play.
Now we will look at how one ant collects food. We will program the ants to work much like leaf-cutter ants. We want them to pick up food and bring it back to their nest. The ants should wander, like the last model. Now, we can also program the forage-food procedure to help the ants forage. Once they have picked up the food, they should bring it back to their nest. If they don't have food yet, they should keep looking.
Now we're going to look at multiple ants who form an ant colony. This model will include a new procedure, called setup-ants, that will determine the number of ants we start with. To set up the ants, we have to hatch a certain number of ants.
With pheromone communication, ants food collection changes. Ants go out to collect food and return to the nest. As they return to the nest, ants lay down a pink pheromone that attracts other ants nearby. Other ants walk toward the strongest chemical smell, which in most cases is where the first ant just passed. When ants find a flower, their food source, they return, lay down more pheromones, and thus reinforce the pink trail. This creates an emergent feedback loop that routes more and more ants to successful sites of forage. As the ants exhaust a food source, they must find new locations and thus repeat the cycle.
We have a new command called drop-chemical. This tells the ants to drop pheromones. When should they drop their pheromones so that they can help other ants find food?
The Pheromones Model also gives you the ability to add pheromones, flowers, vinegar, or laser to the model. Choose what you want to add in the box to the left of the model, and then click on the model while it is running.