Adult lions have no natural predators, though they are certainly vulnerable to threats from humans, especially hunting and habitat destruction. Environmental changes can also impact their food supply, while large animals like rhinos and elephants sometimes trample and kill lions while defending their young.
You wouldn’t expect, however, that an ant species would make much of a difference to an apex predator's survival. Yet their position at the top of the food chain puts lions at risk when small ecological changes impact their hunting practices.
Lions in Kenya are currently facing just such a challenge, and it’s all because of one invasive species. The big-headed ant first appeared in the country around 20 years ago, possibly having hitched a ride via shipping containers or foreign tourists.
The link between big-headed ants and lions isn’t obvious, as they hardly ever interact directly. Instead, it involves several other links in the food chain. One of the biggest impacts caused by the arrival of big-headed ants is that they form supercolonies at the base of whistling thorn acacia trees, then kill the tree's native inhabitants, acacia ants.
Acacia ants have a mutualistic relationship with whistling thorn trees and play an essential ecological role by protecting them from large herbivores such as elephants and giraffes, as well as other insects. When an herbivore tries to nibble the tree’s leaves, branches, or bark, they are swarmed by the ants. In return, the acacia ants rely on the acacia’s naturally hollow spines for shelter and its nectar secretions for sustenance. Unfortunately, when acacia ants are wiped out by big-headed ants, the trees no longer enjoy this effective deterrent that helps them survive.
The presence of acacia trees in East Africa has long been an essential component of lions’ hunting practices, as they rely on them for cover when stalking zebras, preferring to hide behind the trees before leaping out to ambush and chase their prey. Yet with big-headed ants instead of acacia ants residing there, the trees are far more susceptible to being knocked over and eaten by elephants, thus eliminating an important aspect of the lion’s zebra hunting strategy.
Recent studies have confirmed that the loss of acacia ants (and, consequently, acacia trees) is having a noticeable effect on how lions hunt. The whistling thorn trees in Kenya’s Ol Pejeta Conservancy are dwindling, and 75% have disappeared since the big-headed ants’ arrival. That’s good news for zebras, but not so much for lions. The number of zebras killed in the conservancy decreased by 25% from 2003 to 2020. Other research has confirmed that lions are significantly more successful at killing zebras in areas with tree cover.
A tiny ant with a massive impact:
- Thankfully for the lions, they have another major source of prey: African buffalo. This isn't their preferred option, though, as up to 10 lions are needed to kill a buffalo, whereas a zebra can usually be taken down by one or two big cats.
- The continued expansion of big-headed ants has put other animals at risk, like the critically endangered black rhinos that eat whistling thorn trees.
- Around the size of a sesame seed, the big-headed ant (Pheidole megacephala) was first discovered on the island of Mauritius in the 18th century. They have since spread to many tropical and subtropical areas due to ships traversing their Indian Ocean habitat. In addition to taking over acacia trees, they are also infamous for their ability to infest ceilings and tile floors, and chew through electrical wires, phone cables, and irrigation systems.
