Ants - nature’s composters and enslavers
This week I focus on the natural history of ants and the pros and cons of red ants in the garden
Earlier this month, I went to Costa Rica to look at how climate change was affecting the country and was able to enjoy the delights of the rainforest – my favourite habitat – where I spent a lot of time kneeling on the ground, watching leaf cutter ants at work. It was fascinating to watch the columns of worker ants carrying pieces of leaf back to their vast underground nests.
These hardworking ants have the most amazing relationship with a fungus. The ants can’t digest plant cellulose, but the fungus can, so they nurture the fungus in vast underground fungal gardens. In return for providing the fungus with food, the ants feed on the fungus, getting all the nutrients they require.
The worker ants forage for leaves, often travelling long distances to find the right leaves, cut them up and carry them back. And here’s the fascinating bit. When they bring back fresh plant matter, they go to a special chamber to drop it off and then they poo on top of it. Why? When they eat the fungus, they also eat packets of cellulose-digesting enzymes produced by the fungus. The packets remain undigested in their gut and are egested in their poo, whereupon the enzymes are released to kick start the composting process. How clever is that …..
There’s a lot of quality control too. The ants are very careful not to bring back leaf matter that carries bacteria or fungi that might harm their symbiont fungus, and to make sure, there are special compost worker ants that inspect the deliveries and remove any that they think is infected. So you often see piles of rejected leaves outside the entrance to the nest. The ants also pick up antibiotics when they eat the fungus, and this protects the ants and prevents them from harbouring pathogenic fungal spores, which is one of the greatest threats to the colony.
A vast nest underground
A new colony is created when a queen ant leaves a colony on her nuptial flight with an inoculum of fungus that she will use to start her fungal garden underground. She lays eggs, and in a few months, the new colony is up and running. The queen can live for up to 25 years, during which time the colony becomes huge, spreading several metres underground and with multiple chambers and entrances.
There are lot of different classes of worker ants: foragers that leave the nest to find food, soldier ants that guard the foragers and the nest, nursing ants that tend the eggs and larvae, and workers that focus on the compost pile. There is a group of tiny ants that sit on the backs of the foragers to defend them from predatory flies. Interestingly, the composter ants don’t mix with the rest of the colony, as they are at greatest risk of coming into contact with harmful bacteria or fungi.
Underground, the nest has many different chambers while the ground above the nest is cleared of the vegetation, so there is less cover for predators, such as spiders, and its easier for the ants to control the temperature of the fungal chambers.
We saw trails of ants stretching 100s of metres across the floor of the forest. The foragers follow well used routes through the forest, using pheromones to identify the trail. These trails are kept clear of vegetation and debris, and the surface is smooth so the ants can maintain a good speed and be ultra-efficient. However, when there’s a heavy rain storm, the ants get disorientated as the pheromones are washed away. They drop their load and run around looking to pick up the trail again. Usually, the route is active again in a short time and foraging continue.
The foragers manage their food resources in a sustainable way, being careful not to harvest too much from a single source, the plants are not stressed by the defoliation. Also, many rainforest plants have defences against herbivores, so if the ants did too much damage, the plant would up its chemical defences, and the plant matter would be less nutritious.
One of the main predators of the leaf cutting ant is the armadillo. Thanks to a trail of leaf cutters passing our room, we were incredibly lucky to return one night to find an armadillo busy munching on ants outside our door.
Enslaving ants
You don’t have to travel to the tropics to watch ants. There are more than 50 species of ant in the UK, some with fascinating life histories.
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