Why Do Acacia Trees Have Thorns?

Acacia refers to a genus of trees that contain around 160 species. While the acacias in Africa and Australia are the most well-known and recognizable, the different species live all over the world.  Many types of acacia trees have long, sharp thorns that serve a useful purpose. In this article, we’ll discuss how those thorns help acacia trees as well as other creatures survive.

Why is the Acacia Tree Covered in Spikes?

why is the acacia tree covered in spikes

Many of the acacia trees that live in tropical and subtropical areas of Central America, Asia, and Africa are covered in sharp thorns that serve to protect themselves from plant-eaters who like to munch on trees.

Anything from rodents and insects to large animals like giraffes might otherwise destroy acacia trees if it weren’t for its defense system. Not only do these spikes serve to deter certain plant-eaters, but they also provide homes for its other defenders.

How Does the Acacia Tree Protect Itself From Animals?

It seems hard to believe that a tree could have several different ways to protect itself, but that’s just how amazing acacias are. Here are the three main ways that acacia trees protect themselves: 

Sharp thorns

The spiky barbs that cover the branches of many acacia species are great at deterring certain predators. Many animals avoid the tree so that they don’t end up getting stuck or poked by the long thorns. 

Stinging ants

It’s not only the sharpness of the thorns that makes acacia spikes formidable – it also has to do with what lives inside of them. Tiny, fierce stinging ants live in the hollowed-out thorns of acacia trees. 

In a fascinating mutualistic relationship, the acacia ant, or Pseudomyrmex ferruginea, charges rodents, large animals, and other insects to prevent them from eating the leaves of the trees. When a creature approaches, the ants alert each other to attack and sting the animal. 

In return for their services, acacia trees provide shelter as well as sustenance for the ants. Acacia leaves contain vital nutrients for the ants, who are not able to survive by feeding off of any other plants.  

Repellant chemicals 

Bullhorn acacia trees also protect their leaves by emitting a chemical that keeps animals away. When an animal, like a giraffe, starts to snack on its leaves, the acacia gives off a chemical that makes the leaves taste very unappetizing. 

In another amazing turn of events, other acacias miles away can sense this chemical as well, which triggers their defense chemical. Within 15 minutes of a plant-eater munching on its leaves, acacia’s up to 45 miles away can render their leaves inedible. 

This is part of the reason why leaf browsers like giraffes move from tree to tree fairly quickly. When one tree stops tasting good, giraffes will move on to the next. 

How Else Do Acacia Trees Protect Themselves?

Acacia trees don’t just have other animals to worry about. Many of them live in harsh conditions, like the savannah, for example. The acacia trees in the savannah have had to develop some impressive adaptations to survive, such as:


Acacia trees in the savannah have extremely long taproots, which are the main, downward-growing central roots that smaller roots branch out from. These roots can reach deep groundwater sources that help them survive in periods of drought. 


The hot, dry conditions in the savannah mean that wildfires are not an uncommon occurrence there. When the part of the tree that grows above-ground sustains severe fire damage, some acacia species can resprout from the root crown. 

Trees that are above 6-9 feet tall are considered above the “fire trap”, which means that they won’t be burnt back to the roots by fire. So acacia trees have developed the ability to grow rapidly to ensure protection from fires. 

Why Do Savannah Trees Have Flat Tops?

Why Do Savannah Trees Have Flat Tops

Another interesting trait of the acacia tree that has developed over time is their flat shape. This makes them instantly recognizable in places like Africa. 

Here’s what gives them their classic look:

To Prevent Animals From Eating the Leaves

Once acacia trees have grown tall enough to escape the danger of fire damage, they focus on branching out sideways. By growing long horizontal branches, they are able to protect internal branches from leaf-eaters.

There’s No Need For Them To Grow Tall 

In forests that are densely packed with trees, they have to compete with other trees for light. This means that trees grow very tall to reach as high above neighboring trees as they can. 

Savannah trees such as acacias don’t have the same competition for light, so they don’t need to be as tall.  

Acacia trees are tough as nails and have survived perilous conditions thanks to their adaptability. Instead of being decimated by other creatures, fires, and drought, the trees evolved to withstand those dangers.

If you’re interested in learning more about the Savannah biome, this video has tons of interesting information:

2 thoughts on “Why Do Acacia Trees Have Thorns?”

  1. I have an acacia tree in my garden.
    I am now experiencing lots of thorns being dropped on the ground from the tree and causing problems with my neighbor’s .
    The tree is about 10 years old and never experienced so many thorns dropping like this before.
    Do you know the reason why????


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