Acacia cornigera, also known as the bullhorn acacia tree, is known for its large thorns that are teeming with stinging acacia ants. In its native habitat in Mexico and Central America, the two species have a unique relationship that has been fascinating to scientists for many years. In this article, we’ll talk about the symbiotic relationship between ants and acacia trees, and how they help each other survive.
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What is a Symbiotic Relationship?
Symbiosis is a term that is used to describe a close relationship between at least two different species. Sometimes, the relationship benefits both creatures, and sometimes only one sees the benefits.
When both creatures benefit from their symbiotic relationship, it is considered mutualism. Since stinging ants and bullhorn acacias both benefit from each other, most researchers agree that they have a mutualistic relationship.
How Do Ants Protect Acacia Trees?
Pseudomyrmex ferruginea, or the acacia ant, are small stinging ants that live among the swollen thorns of the bullhorn acacia tree. The tree relies on these ants to defend its leaves by attacking hungry herbivores that try to snack on the leaves.
Giraffes, for example, love to munch on the tops of trees. But when they start to eat the bullhorn acacia’s leaves, they’re greeted by a face full of tiny stinging ants and quickly reverse course.
The ants give off a chemical signal when plant-eaters approach that alerts the other ants to join in and attack. Without the ants, bullhorn acacia trees would get eaten by everything from grasshoppers to small rodents like mice.
Acacia ants also consume any unwelcome plants that start to grow around the tree. The tree benefits from this, because now they don’t have to compete for resources, like water and sunlight, with other plants in the area.
In addition to protecting the tree from other creatures, researchers have discovered that the ants also reduce the presence of harmful bacteria on its leaves.
Scientists from the Max Planck Institute for Chemical Ecology in Germany recently found that the presence of mutualistic ants on bullhorn acacia trees significantly decreased the likelihood of leaf damage from negative pathogens.
How Do Acacia Trees Benefit Ants?
In return for protecting them, bullhorn acacia trees provide two vital things to acacia ants:
The leaves of acacia trees contain sweet nectar that acacia ants have become dependent on for survival. The tips of the leaves contain sacs filled with valuable nutrients, which adult ants eat and feed to their larvae.
Research completed in the early 2000s suggests that acacia ants are so dependent on the tree’s nectar that they aren’t able to digest normal sources of sucrose (the sugar ants get from plant sap). So in a way, the tree manipulates the ants into protecting them by providing exclusive nutrients that they can’t get elsewhere.
Ants live inside of the thorns of bullhorn acacia trees. When bullhorn acacia trees develop the thorns, the centers of the thorns are a soft green structure.
The ants consume the soft centers and then live within the hollowed-out sections of the thorns, only coming out to feed on nectar from the leaves and protect the tree from other creatures.
Do Ants Hurt Acacia Trees?
There are some species of ants and acacias whose relationship is more parasitic in nature, meaning that only one species sees any benefits. The Acacia drepanolobium, or whistling thorn tree in Africa, is a good example of this.
Whistling thorns have a few different species of ants that compete for real estate on the trees. In some cases, the ants feed on new growth on the trees, preventing the tree from growing. They also will eat the flower and leaf buds, thus eliminating the tree’s ability to reproduce.
Unlike the harmful ant species, the bullhorn acacia’s ants seem to help with reproduction. Acacia plants produce flowers, which need to be pollinated for the tree to reproduce.
Although stinging acacia ants love the nectar the leaves produce, something prevents them from feeding on the nectar from the flowers. And despite attacking any creature that tries to eat the leaves, the ants leave the pollinators alone while flowers are blooming.
Scientists believe that the flowers give off a chemical that repels the ants to protect themselves during the time when they’re producing the most pollen. Once that pollen is mostly gone, the flowers don’t deter the ants as much and they start to return.
If you are now even more amazed by nature’s incredible ability to thrive in such unique ways, you’re not alone. Symbiotic relationships are fascinating and have helped keep many plants and animals going for thousands of years.
To see more examples of incredible symbiotic relationships, check out this YouTube video: