Yes, ants are cannibals. Some ants turn to cannibalism for nutrition and survival in times of scarcity. Queen and worker ants alike, practice cannibalism when needed.
In 2016, scientists described a colony of ants trapped in an old nuclear bunker. These ants had no access to food and had to survive by feeding on the corpses of their dead nestmates.
In total, they discovered about two million dead ants and one million live ones in the bunker. These were millions of ants that engaged in cannibalism.
In this article, we’ll learn more about cannibalism in ants as we discuss the following:
- Definiton of cannibalism
- Which ants are cannibals
- Why do ants engage in cannibalism?
As opportunistic eaters ants eat other ants. So we’ll need to differentiate cannibalism from regular predatory behavior.
By definition, cannibalism refers to feeding on another member of the same species. Meaning it only includes internal fighting and predation between the same species. For example, carpenter ants eating other carpenter ants is cannibalism. Them eating weaver ants, however, is not. 
Which Ants Are Cannibals?
Aggressive ants are usually the ones that practice cannibalism. Fire ants, for example, are notorious for attacking other ant colonies. These colonies may be of other types of ants or their own species.
Whenever fire ants attack, it usually escalates to small skirmishes or all-out wars. Any ants that die from these fights end up eaten.
Fire ant queens have also been found to cannibalize their diploid male larvae. They do so as a strategy to lessen the cost of inbreeding. When they eat these males, they reclaim nutrients to redirect to workers and other larvae.
With all that said, cannibalism isn’t limited to just aggressive ants. Even the more passive ones like carpenter ants and wood ants cannibalize their own as needed.
Wood ants, for example, are known to exhibit cannibalistic necrophagy. This means that they eat their own dead. In fact, the very ants that survived the old bunker are of the wood ant species Formica polyctena. 
If you think cannibal ants are disturbing, there are also cannibal larvae.
The larvae of the wood ant species Formica aquilonia are cannibals. Those fortunate enough to hatch first, find other eggs and eat them to gain strength. 
Why Do Ants Engage In Cannibalism?
Ants engage in cannibalism for survival. Ants are generally capable of sustaining themselves through foraging. However, they turn to cannibalism for nutrition in times of scarcity. Case in point, the trapped wood ants had no choice but to eat their nestmates due to a lack of other food sources.
Survival is also the reason why fire ant queens eat their diploid male larvae. Note that these diploid males tend to grow into sterile ants. As such, they are useless for colony growth. Eating them allows queens to reclaim and reuse nutrients to produce better offspring. 
Other Reasons for Cannibalistic Behavior
Apart from survival, there may be other reasons why ants engage in cannibalism. For example, cannibalism might be linked to ant politics. 
Cannibalistic larvae tend to target eggs from different families. This does not provide any benefit to the colony but strengthens one family over others.
Scientists have also considered cannibalism as part of an ant’s hygienic repertoire. Some ants may eat their dead to prevent future encounters that may lead to infections.
Do Ants Eat Their Dead?
Yes, some ants do eat their dead. This behavior is called cannibalistic necrophagy. It is observed in certain ant species including F. polyctena.
Why Do Ants Carry Their Dead?
Ants carry their dead for hygienic purposes. They transport their dead to a graveyard to prevent them from spreading disease.
See this article to learn more about why ants carry their dead.
Do Ants Fight Each Other?
Yes, ants fight each other. In fact, ants have been fighting for millions of years. Ant colonies commonly engage each other in fights as they compete for resources. These fights sometimes grow into all-out wars where casualties can reach thousands.
See this article to learn more about ant fights.
Summary: Are Ants Cannibals?
To summarize, ants are cannibals. Some ants like wood, carpenter, and fire ants feed on their own kind for sustenance. To them, cannibalism is a means of survival.
They see cannibalism as a viable behavior in times of food scarcity. Queen ants even use it as a strategy to ensure colony growth and health.