Animal Cannibalism: Animals that Eat their Own Species

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Cannibalism is often the topic of horror movies and something that humans recoil in disgust at. But that’s only because it’s not a normal trait of our species. However, if you look into nature, cannibalism is far more common than one might first be led to believe.

Forms of Cannibalism in the Animal Kingdom

When you think of cannibalism, you probably imagine one of the same species eating another member of that species. This is known as intraspecific cannibalism. But there is a second type known as interspecific cannibalism. Let’s take a look at the differences.

Intraspecific Cannibalism

Intraspecific cannibalism is what most people imagine when they think about cannibalism. It involves one member of a species eating another member of the same species. In many  cases, this type of cannibalism is something that has naturally evolved over time for various reasons, including diet expansion or a lack of resources. As this happened, some species have physically adapted to this behavior. However, we have to keep in mind that intraspecific cannibalism can have a knock on effect on population and interaction between members of the same species.

Interspecific Cannibalism

Interspecific cannibalism is quite different in that it involves a member of one species eating an individual of another species. In many cases, this is done as a means of survival and in some cases, animals will prey on others as part of gaining additional nutrition for reproductive purposes.

Typically, this type of behavior is limited to areas where there are limited resources and animals are forced into interspecific cannibalism to survive. It’s worth noting that interspecific cannibalism may not always be the norm but could be triggered by environmental factors. But just like intraspecific cannibalism, this form can also have a significant effect on populations within an ecosystem.

Since this type of cannibalism has evolved over time, animals have gradually adapted. Not only do the predatory species have special adaptations to help them hunt, but prey species have developed  defense tactics as well.

Reasons for Intraspecific Cannibalism in the Animal Kingdom

Imagine being forced into cannibalism; there’d have to be some pretty extreme excuses for this behavior, at least where humans are concerned. And it’s not all that different in the animal kingdom. In fact, cannibalism isn’t typically something that happens without a reason.

Nutritional Benefits

In order to survive, an animal needs the correct nutrition, but this isn’t always available without consuming a member of its own species. This is typically a type of intraspecific cannibalism and occurs when individuals need high-quality nutrition that’s easy to digest, particularly when protein is required for reproduction or growth.

In an environment where nutrients are scarce, behaving in this way gives the species a higher rate of survival. What’s more, where reproduction is concerned, cannibalistic behavior may increase the chances of success because of greater access to important nutrients. When the young are born, they’re able to consume important nutrients right from birth, ensuring healthy growth.

Not only would the prey contain all the essential amino acids and nutrients, but studies have also shown that by cannibalizing, the predator can take advantage of its victim’s diet.

That said, while some cannibalism related to nutrient acquisition is intentional, there are examples of animals resorting to this behavior in environments where nutrients are otherwise scarce.

Environmental Stress

Leading on from my last point, there are instances when animals encounter situations of extremely limited resources. To survive, they may resort to cannibalism. However, cannibalism isn’t solely about acquiring nutrition; it could also entail intentional attacks to secure a nesting spot or territory, for example.

They say it is survival of the fittest, and this is true. In these stressful situations, animals must compete for resources and when things get heated, some species are not afraid to do the unthinkable. When fighting for territory, it’s not uncommon for things to get very aggressive.

Resources may become limited for many reasons, including changes in the weather, migration, and a change of season. However, in some cases, cannibalism is a natural response to overpopulation. The stress that comes with high population density and limited resources can trigger this behavior in certain species.

Reproduction

Most people have heard the myth that certain spiders eat their mates after copulation is complete. But let me tell you that this is not a myth; just a fact of nature! It’s very common among arachnids and insects, such as the praying mantis and the scorpion.

One of the primary reasons for this type of cannibalism is to reduce reproductive competition. If you eat your rivals, you’ve got a greater chance of finding a mate. But some species will even eat other members of their species to make themselves more attractive to potential mates as part of a greater courtship ritual. Some species, like the dark fishing spider will even give themselves up for cannibalism after mating in the ultimate self-sacrifice.

There may also be instances where consuming a mate means that there are fewer threats to the offspring once it is born and is a method of protection. Moreover, sometimes, consuming a member of the same species provides the mother with more nutrients, which contribute to the development of her young.

At other times of the year, these animals may show no cannibalistic tendencies. But when mating season rolls around, hormonal triggers can influence their behavior. This is very common in species where there is obvious sexual dimorphism and is often a way of showing dominance over the weaker mate.

Population Control

Where populations get out of control, this leads to heightened competition for resources like food and territory, and that’s not good news for individuals. So, some species have evolved intraspecific cannibalistic traits that are triggered by environmental conditions and hormonal responses when populations become too dense. 

While it might seem harsh, this is nature’s way of ensuring effective population control, and it’s typically the weaker members of species that will be preyed on. This is also beneficial as the stronger individuals will survive and go on to produce stronger, more viable offspring for the continued survival of the species.

However, cannibalism for this reason is also essential for the protection of the ecosystem. Where species populations are allowed to get out of control, this can lead to a depletion of resources and ruin the health of an ecosystem.

Territorial & Resource Competition

Just like humans, animals need somewhere they can call home, and in the wild, they’ll often claim their own territory but where this isn’t available, things can get very heated. In areas where there is limited space, it’s hard to claim territory, and this also comes with the issue of a lack of access to other resources like food.

In order to get their hands (or hooves, paws, trotters) on the best resources or breeding sites, animals may resort to cannibalism to wipe out the competition. When this happens, it also puts the predatory individual in a place of dominance, showing others that it is the strongest and not to be messed with.

With this kind of reputation and by eliminating rivals, individuals who cannibalize may also be more attractive to potential mates, giving them a greater chance at reproductive success.

It is worth noting that while many species have adaptations that aid their cannibalistic behaviors, this may not always be a first resort. When fighting for territory, animals may typically display aggressive behavior and attempt to fight their rivals. Cannibalism is usually one of the last tactics used to obtain victory.

Parental Care

You’d do anything to protect your kids, right? The same can be said for animals, many of whom will often turn to cannibalism as a way of providing nutrition to their young. In some cases, the parent may even prioritize certain offspring over others. For example, she may provide more nutrition to the strongest sibling that has a greater chance of survival.

But, it isn’t always an unlucky passerby that becomes a meal; in fact, in a lot of cases, the parent will offer one of the weaker siblings as a meal for its strong brother or sister. There’s no room for emotion in the animal kingdom, and that’s further backed by the fact that some mothers will even consume their own offspring!

This may be as a method of population control or could occur when the mother feels as though the environmental conditions aren’t quite right for raising her young. This is known as filial cannibalism and is described as a parent consuming part or all of its young.

Social Dynamics

I’ve already touched upon the importance of dominance in terms of gaining territory, and many animals have a hierarchy that dictates how they socialize. The higher up an individual is, the stronger and more dominant and therefore, more likely to engage in cannibalistic behavior.

Not only does this give them a chance to remind everyone who’s boss, but it also helps that individual retain its position within the social structure.

But that isn’t to say that these animals go around eating each other for the fun of it. This behavior is usually triggered by an aggressive interaction, stress, mating competition and other factors. What’s more, if another individual wants to fight for territory, the dominant member won’t think twice about cannibalizing if that is what is needed to protect their territory. This is especially common in areas where there is a lack of resources which need protecting.

So, where do these animals pick up this trait? Well, while there may be some kind of primal instinct going on, many actually learn how to do this by watching more dominant peers engaging in cannibalistic behavior.

What really fascinates me is that there seems to be a degree of compassion in some animal cannibals. For example, there’s a species of tadpole that, when studied, was seen to favor non-siblings over its own relatives when it came to eating members of the same species. At least there’s some family loyalty!

Animals that Practice Intraspecific Cannibalism

While it might seem heinous to humans, there are many within the animal kingdom that thrive off feasting on one another. And some of them may surprise you.

1. Praying Mantis (Mantodea order)

If there’s one creature that’s well known for its cannibalistic tendencies, it’s the praying mantis. These insects primarily turn to cannibalism during the mating season, when the females are known to eat the males both before and after breeding.

Whether she eats the whole male or just part of him, the females do this as a way of getting important nutrients to ensure successful reproduction and increased fertility. It’s not something that all species do but is nonetheless very common, for example, the springbok mantis.

Interestingly, males don’t go down without a fight. In the case of the springbok mantis, there will be an aggressive struggle between the two. Where the male wins, copulation is inevitable but if the female wins, she gets a free meal and doesn’t have to mate. When choosing a mate, the female will typically opt for a stronger, larger male who contains more nutrients and is therefore more beneficial as a meal.

With that said, it’s more likely that a female will engage in cannibalism when she’s hungry. While it’s said that all females devour their mates, this isn’t strictly true. It’s certainly common but a female is less likely to do this when she’s already well fed.

2. Polar Bear (Ursus maritimus)

The polar bear is a species known for its aggression, but most people don’t realize that these beautiful animals are capable of cannibalism. And they may do it more often than we think. 

This is an interesting adaptation to environmental conditions, as cannibalism seems to be becoming more common in this species. While the main diet of the polar bear consists of seals, food is becoming more scarce because the ice caps are melting, decreasing the hunting ground for polar bears.

The result? They’re turning to eating one another. This is particularly common in seasons where food is very limited, and the behavior is typically exhibited by males who attack the weaker females and cubs.

While this is happening across polar bear territory, research has shown that the bears in Norway are primarily affected. It’s a sad story of how climate change and human disruption is forcing our wildlife into aggressive new behaviors. 

3. Desert Spider (Stegodyphus lineatus)

Spiders are among some of nature’s most famous cannibals, and the desert spider is a great example. In this case, we’re talking about matriphagy, which is a behavior in which females are eaten by their young.

It might seem weird, but it’s actually a lot more common in nature than we would imagine and a normal part of many species’ reproductive strategies. Where food is scarce, the mother willingly sacrifices herself for the nutritional benefit of her offspring. Without this sacrifice, the spiderlings would struggle to develop and survive and that has a direct impact on the survival of the species and their genetic success.

Matriphagy is thought to be an adaptation of the desert spider and typically happens at a stage when the spiderlings are too vulnerable to be able to hunt for themselves. Instead, the nutrients of the mother’s body ensure successful growth and healthy development.

But even where females don’t need to go through matriphagy, there’s still a risk that they may lose their life during the reproductive cycle. It’s not uncommon for males to remove eggs and force the female to use their sperm. However, this is stressful for the female, and it’s shown that there’s a 23% more chance of death when this happens. 

4. Hamster (Cricetidae family)

I bet you never imagined your cute furry pet had the capacity to show an aggressive tendency like cannibalism. But as sweet as they may be, female hamsters may actually devour their young. That said, they typically only do this when they think there’s a threat to the offspring and cannibalism is the lesser of two evils.

Moreover, it’s not uncommon in the wild for hamsters to turn on one another when populations become too dense or food becomes scarce. Cannibalism is a way of reducing the competition for resources and ensuring survival of the fittest. It’s happening at an alarming rate with wild hamsters in France where their diet is being affected due to agricultural practices.

Female hamsters may also become easily stressed when caring for their young, and these environmental stressors could cause them to cannibalize their babies. For this reason, pet owners are advised to keep a close eye on new mothers and separate them from their young after the initial nursing period.

5. Caecilian (Gymnophiona order)

The caecilian is a type of legless amphibian, often mistaken for a worm, and while it is considered to be cannibalistic, its behavior differs slightly from other animal cannibals.

When the caecilian mother gives birth to her live young, they’re still in need of a lot of nutrition. Because she’s not a mammal, she doesn’t produce milk to sustain her young but she has another, rather interesting way of doing this. She grows an extra layer of skin that her young can feed on and it’s packed with protein and fat to ensure healthy growth and development.

So effective is this food that the young have been known to grow up to 86% in as little as 20 days after being born.

It’s a form of matriphagy known as maternal dermatophagy, but in this case, the mother does survive the ordeal. She’ll even grow new layers of tasty skin to keep feeding her young.

6. Sand Tiger Shark (Carcharias taurus)

Mammals rely on nutrition being passed to them through their mother’s blood stream during pregnancy. But fish are slightly different, and in the case of the sand tiger shark, it’s a pretty extreme form of pre-birth feeding.

Sand tiger sharks typically give birth to two pups each year, and this is pretty low where shark reproduction is concerned. But maybe that has a lot to do with the fact that baby sand tiger sharks eat their siblings while still in the womb in a process known as intrauterine cannibalism. Essentially, the larger embryos feast on their smaller, weaker siblings to further enhance their own growth.

Females have two uteruses and to begin with, there are several eggs in each. In the first part of the process, known as oophagy, the bigger embryos will eat any unfertilized eggs. But when these resources are depleted, they’ll move onto consuming the smaller embryos in a part of the process known as adelphophagy. By the end, after an aggressive competition that reveals the strongest and largest individual, only one pup survives in each womb to be born.

This might sound horrific but there are advantages to this behavior. For starters, the pups that survive until birth are the strongest and therefore have a better chance of survival and going on to reproduce themselves, especially considering that at birth, the pups are already significantly self-sufficient. Moreover, with fewer siblings at birth, there’s less competition for resources on the outside.

7. Black Stork (Ciconia nigra)

The black stork is a species of aquatic bird that usually feeds on a diet of fish and invertebrates. However, where resources become limited, it is not unheard of for the adults of this species to feast on their young to sustain themselves.

While this doesn’t happen as a matter of course, when it does, the black stork can become seriously aggressive in order to protect its territory and claim its share of the resources such as food, mates and nesting spots. Where things get really heated, they can and will resort to cannibalism.

As I mentioned, parents will turn on their offspring when there is a serious lack of resources in a phenomenon known as parental infanticide, but this is usually triggered by factors such as stress, climate change, or when the nesting site is disturbed.

Of course, when this occurs, the number of chicks in any given brood that survive is drastically reduced but interestingly, studies have shown that this has very little effect on the monopolization of food resources among the surviving individuals. 

8. Cichlid (Cichlidae family)

If you own an aquarium, you may have been told never to keep cichlids together, especially during breeding season. There’s a good reason for this. The males of this species can become incredibly aggressive when it comes to finding a mate, and they won’t think twice about attacking others or cannibalizing eggs. 

But it’s after the young are born that things get really interesting, with African cichlids displaying traits of filial cannibalism. That’s right, the mothers will eat their own offspring. 

Cichlids are mouth brooders, meaning that the mother will carry her eggs and newly hatched young in her mouth to protect them. However, as the offspring grows, it can be challenging for mom to keep up with the demand of a constantly full mouth, so she counters that by eating some of her children. 

What’s more, the mother gets a significant nutrient boost from doing this, giving her the energy required to keep caring for the remaining young.

9. Chimpanzee (Pan troglodytes)

Chimps are said to be one of our closest living relatives, but there’s one thing that we certainly don’t have in common, and that’s the potential for cannibalism.

Also known for their potentially aggressive nature, chimpanzees aren’t afraid to get into a scuffle with one another. In fact, it’s a lot more common than you might think for chimp families to attack one another and, in a display of dominance, one family may take a weaker member of the other and consume it. In some cases, they may even eat one of their own as was documented back in 2017 when a previous alpha male was eaten by his own group.

What’s more, there has been a sighting of a female chimp giving birth and, shortly after, her offspring was taken by a large male who proceeded to devour it. This happened after the female gave birth in the presence of other chimps whereas usually, mothers would take themselves away from the group to deliver. Scientists propose that the reason for this could be to avoid such incidents. However, very rare cases of maternal cannibalism in chimpanzees have been reported.

10. Tiger Salamander (Ambystoma spp.)

The tiger salamander is known for its intraspecific cannibalistic tendencies, and it’s been observed that larger individuals may prey on their smaller, weaker counterparts when food becomes scarce. Since these are ambush predators, those smaller members of the species don’t even see the attack coming.

But this isn’t just something that occurs when the tiger salamander is an adult, it begins during the larval stage when larger individuals will feed on smaller ones. It’s thought that those that engage in this behavior during the larval stage have an immediate size advantage throughout their lives. As they go through the various stages of life, including during their metamorphosis, these individuals will be more likely to continue with their cannibalistic behavior. Interestingly, however, studies have shown that individuals raised in mixed brood groups were more likely to display cannibalistic traits.

As well as using cannibalism as a way of managing a drop in resources, the tiger salamander may also resort to this behavior during breeding season. Much like other animals, this is a tactic to eliminate competition and be more likely to get a mate.

11. Crab Spider (Misumena vatia)

Another species of arachnid for which cannibalism is not unusual is the crab spider. As is the case with many other insects, this cannibalism is driven by breeding, and females may eat their mate after doing the deed.

It’s thought that this is part of the overall reproductive strategy and benefits the female by providing her with additional nutrition both for herself and her developing young.

But it’s almost as if the male knows the risks, and despite his desire to mate, he’ll still try to impress the female with an elaborate courtship ritual in the hopes that he’ll impress her enough to avoid becoming dinner. But there are cases where he’ll accept his fate and may even sacrifice himself during the mating process. Talk about taking one for the team!

That said, females are pretty picky and are very selective when it comes to choosing a mate, especially when his size and quality are taken into consideration. Not only do these males provide the most nutrition, but their genes will also ensure healthy offspring.

While it is very common for females to eat the males after copulating, it doesn’t always happen. In fact, it’s been observed that this type of cannibalism is more common in situations where food is scarce, proving that animal cannibalism is, in fact, often triggered by environmental factors.

Researchers have shown a lot of interest in the crab spider and its cannibalistic behavior, even noting that some spiderlings will spend much longer in the nest, growing at a rapid rate because of early cannibalistic behaviors that encourage faster growth.

12. Dyeing Poison Dart Frog (Dendrobates tinctorius)

When baby dyeing poison dart frogs are born, they’re in tadpole form, and the parents will transport their young to a special ‘tadpole pool’ where they will develop. The problem is that there are likely other tadpoles in this pool and they’re all very aggressive cannibals.

However, the frog fathers have been observed dropping their young off in pools where there are already decent sized tadpoles as this signals that there is potential for healthy development. The risk of cannibalism is an unfortunate risk they’re willing to take.

It’s a heated battle for resources in the pool, but studies have shown that tadpoles are more likely to show cannibalistic tendencies towards their non-siblings. Should individuals make it through their metamorphosis and into adulthood, all of their previous cannibalistic urges seem to fade away. 

13. Betta Fish (Betta splendens)

Sometimes called the Siamese fighting fish, the very name of the betta is enough to tell you about its aggressive nature. And it’s all because of how territorial these stunning fish are and, if any other member of the species wants to put up a fight, it could end up in one cannibalizing the other.

This type of aggression is often documented among the male members of the species who fight for territory as well as for a mate. But truth be told, bettas are solitary fish, so these kinds of interactions generally only happen where there are overcrowding problems. This is why aquarium owners are advised to keep them separate, especially males who will fight to the death. That said, through the use of gradual introductions to the tank and an adequate food supply, aggression is less likely.

What’s more, even though males will fight for a mate, they may still show aggressive tendencies towards their female counterparts during breeding. They’ve even been known to show the potential to attack the young. It is therefore best to keep adults and fry separate to increase the chances of survival for the offspring.

14. Harlequin Ladybug (Harmonia axyridis)

The ladybug is one of nature’s prettiest insects, but while it’s beautiful, the harlequin ladybug hides a horrific secret! Now, before I get into it, I should point out that cannibalism isn’t a characteristic that these bugs demonstrate on a daily basis. It’s usually the result of environmental changes and conditions.

Cannibalism can be seen in the harlequin ladybug when populations become too dense and there’s a fight to claim territory. Moreover, where food and other resources are scarce, these insects may resort to attacking and eating each other as a way of limiting competition.

It’s more likely to be the male harlequin that would behave in this way particularly when he’s looking for a mate. However, while it may seem harmful to populations to be eating one another, it’s actually been shown that cannibalism among harlequin ladybugs is an effective way to control dense populations. It’s also this cannibalism that makes this such an effective invasive species, among other traits like quick breeding times and a varied diet. 

And this behavior is not limited to adulthood, in fact, it may be even more prevalent during the larval stage of life, especially where there is a fight for resources. Those that cannibalize are more likely to develop into strong, healthy adults.

15. Hippopotamus (Hippopotamus amphibius)

While it might look like a gentle giant, the hippo is actually one of the most aggressive animals on the planet and its aggression isn’t only reserved for members of other species.

No, the hippopotamus has cannibalistic behaviors that are surprising since the diet of the hippo largely consists of plants. That said, they are classed as omnivores as they have occasionally been seen feeding on animal carcasses, which sometimes include those of other hippos. 

This is extremely rare and is usually only documented when there is a lack of resources, particularly in times of drought. However, a hippo in Kruger National Park was caught feasting on one of his own when the environmental conditions seemed to be perfect. Naturally, this has left researchers baffled. 

One of the biggest concerns with this is that hippos consuming other members of the same species could be susceptible to disease, and this has been reported in Uganda, where many cannibal hippos died after an outbreak of anthrax. 

16. Widow Spider (Latrodectus spp.)

Out of all the spiders, the widow spider is probably the most prolific cannibal in the arachnid kingdom. The female of this species is known for devouring the male after mating, although I’ll hand it to him, he does his best to avoid being her next victim.

While some males use their strong back legs to literally spring away from the female, others will only mate with females that aren’t yet big enough to eat them.

But the question remains, why do the females want to devour their mate? In many cases, females eat the male for nutrition benefits, but since the male widow spider is much smaller, this doesn’t make a lot of sense. Some say it’s for entertainment purposes, while others argue that the female does this to show her sexual preference, with less attractive males more likely to be eaten. During her life, she may mate with and consume several males. 

However, she shouldn’t get too comfortable with her role as the dominant one, as there are plenty of examples of roles being reversed and the males devouring the females. This typically happens when the female is older and, rather than mate with her, the male will make a meal out of her. 

17. Octopus (Octopus spp.)

The octopus is one of the most intelligent animals in our oceans, but they’re also known for their tendency to display cannibalistic behaviors.

Interestingly, this isn’t something that we’ve been entirely sure about, but in 2014, researchers finally captured a male octopus eating the corpse of another octopus on camera. It’s thought that because of the nutritional value of octopus meat, this is done to gain energy. This gave us a new insight into the behavior of these mysterious creatures. 

But now onto the really fascinating part of octopus cannibalism; they do it to themselves! That’s right, female octopus will lay their eggs and take care of them with some of the greatest attention in the animal kingdom. But then, just before her eggs hatch, she seemingly loses the plot!

Owing to a shift in steroid hormones, the mother octopus begins literally starving and beating herself to death in one of the most aggressive examples of self-destruction in nature, even munching on her own arms.

18. Mormon Cricket (Anabrus simplex)

When food sources begin to deplete, it’s not uncommon for animals to start swarming in search of nutrition. In the case of the mormon cricket, this happens every spring and summer as they band together and create large ground as they go looking for protein.

This swarming behavior helps to protect them from predators, but what about protection from each other? You’d like to think that you wouldn’t need protection from your own, but if you’re a mormon cricket, there’s a risk of being eaten by one of your group.

The funny thing is that it’s something of a catch-22. The crickets come together in search of food, but so hungry are they that crickets joining the back of the procession may try to feed on existing members of the group. Don’t join the swarm, go hungry. Join the swarm and risk being eaten. These poor critters can’t catch a break.

With millions of members in a swarm which could spread over 6 miles (10 km) in length, it’s safe to say that food is very scarce. It’s for this very reason that the crickets not only consume all vegetation in their path but also each other!

19. Pea Aphid (Acyrthosiphon pisum)

The pea aphid is considered to be herbivorous but closer research has shown that these tiny creatures not only feed on the eggs of other insects, but also on each other!

The female pea aphid produces an incredible number of offspring at any one time, and they’re all genetically identical. In most cases, the young will feed on plants, but if there’s ever a time that food runs out, they turn to their parents for help.

And I don’t mean that mom goes out in search of an alternative food source; I mean that she is the food source! That’s right, those baby pea aphids start sucking on their mother’s blood like little vampires. While adults have been seen displaying cannibalistic behaviors, studies have shown that it’s far more prevalent in juveniles.