Yes, ants eat aphids. Aphids, like many other insects, serve as a food source for ant predators. They provide ants with the protein they need for colony growth and expansion.
Most of the time, however, ants and aphids form a mutualistic relationship. Instead of eating aphids, ants protect them in exchange for honeydew.
In this article, we’ll learn about the complex relationship between ants and aphids. We’ll discuss their mutualism and the factors that push ants to prey on aphids instead.
Ant and Aphid Relationship
Ants and aphids usually form a mutualistic relationship. This means that they cohabit and benefit from each other. In this relationship, ants become dairy farmers. They tend to aphids in exchange for honeydew.
This honeydew is a sweet, sugary, waste excretion that aphids produce. It serves as a food source for ants similar to nectar and sap.
Therefore it’s easy to see why ants go the extra mile in tending to aphids. In doing so they gain access to a potentially unlimited food supply.
Here are some of the things that ants do for aphids:
- Protect them from predators like lacewings and ladybugs
- Protect them from fungal outbreaks and other lethal diseases
- Care for their eggs
- Provide them warmth and shelter during winter
- Move them to plants ideal for feeding
Why Do Ants Eat Aphids?
Despite their mutualism, ants sometimes feed on aphids for the following reasons:
Honeydew’s great but ants need protein. Protein is essential for colony growth and expansion. Therefore, ants don’t mind eating aphids when protein sources are scarce.
Ants are particular with the aphids they tend to. Some aphids produce higher-quality honeydew and are much more attractive to ants.
Studies show that ants prey on the lesser preferred aphids to make space for preferred ones. 
Ants don’t just go willy-nilly when farming aphids. They plan things out and make sure that they’ll continuously have food for long periods.
Part of this planning involves keeping plants in a certain state of health. They don’t want plants to die off or flower as either can cause the death of aphids.
Thus, to maintain plant and herd longevity, ants eat aphids for population control. 
Ants aren’t shy of betraying aphids when there are better alternatives. Some ants, for example, prefer to form a relationship with acacia trees. 
Instead of tending to aphids, these ants eat them and other plant predators instead. They do so to protect the acacia tree in exchange for shelter and nectar. Perhaps honeydew isn’t as sweet.
Ants can either prey on or tend to aphids based on familiarity. Ants generally tend to aphid species which they have tended to before. Inversely, they prey on aphids which whom they have never interacted with. 
Ants are brutal. They don’t care for weak or unproductive aphids no matter how long they’ve cared for them. Any aphids they deem a liability get eaten for protein. These aphids typically include the sick, old, and weak ones.
It’s all about resource management. Ants don’t want to keep these aphids around as they cost resources to maintain. The removal of sick aphids also ensures that the others remain healthy.
Can Aphids Survive Without Ants?
Aphids can survive without ants. In fact, some aphids don’t rely on ants at all. These aphids have structural and behavioral defenses to help them fight off predators. 
They, for example, use alarm pheromones and dropping behavior to avoid predators. Physically, they can also release waxes to make themselves less palatable.
On the flip side of things, there are also aphids that can’t live without ants. Aphids used to being attended by ants don’t develop anti-predator defenses.
Some can’t even excrete honeydew unless stimulated by the latter.
Do Ants Enslave Aphids?
Enslave is a strong word but the relationship between ants and aphids can be viewed as slavery. Despite the mutualism, ants really only care about honeydew. That is why they can easily discard and eat aphids as they see fit.
Ants also prevent aphids from dispersing. Ants sometimes tear wings off aphids to prevent them from dispersing.
A recent study has also shown that ants use chemicals to subdue aphids. Scientists believe that ants use tranquilizing chemicals to keep aphids near their colony. 
To summarize, ants do eat aphids. While usually best buddies, ants prey on aphids for the following reasons:
- Food scarcity
- Honeydew preference
- Plant health
- Better alternatives
- Low productivity
At the end of the day, ants do what’s best for them. They cease their relationship with aphids whenever deem necessary.