You may already be familiar with various instances of cannibalism in the animal kingdom. For example, female mantises will bite off the heads of their mates and devour them immediately after mating.
A similar behavior occurs in the black widow spider. They are named as such because the female black widow also consumes her mate. Right after becoming a wife, she transforms into a widow herself.
Some other animal species have been observed eating their own siblings, such as the purple toad, where larger tadpoles may consume their smaller siblings.
In sharks, this fratricidal behavior occurs even earlier, right inside the mother’s womb. Healthier embryos will eat the weaker ones, ensuring they are born with the highest survival advantage.
However, among these seemingly brutal behaviors, there is one act that appears even more cruel and nearly unforgivable: some animal species have been caught in the act of eating their own offspring.
While there is a saying in folk wisdom, “A fierce tiger does not eat its cubs,” these species defy that norm. But why do they resort to such actions? Let’s explore their reasoning:
“If anyone intends to eat my young, I’d rather eat them first.”
This cold response comes from a mother Long-Tailed Sun Skink. By human standards, these female skinks are undoubtedly terrible mothers. After laying their eggs, they abandon the nest, leaving the eggs unprotected.
However, a population of Long-Tailed Sun Skinks living on a Pacific island seems to exhibit a bit more responsibility. They often guard their eggs for a week to ensure their hatchlings have a better chance of survival.
Evolution has developed a maternal instinct in this population of skinks, as the island they inhabit is home to a snake species (Oligodon formosanus) that specializes in preying on skink eggs.
When a snake invades the nest, the mother Long-Tailed Sun Skink will immediately fight fiercely to protect her eggs. She seems like a model mother, doesn’t she? But a tragedy can occur if the frequency of snake attacks is too high.
A study conducted in the wild in 2008, along with field experiments, found that if snakes frequently attack skink nests and the females realize they can no longer fend off the snakes, the mother skink will consume all her eggs before the snakes can eat them.
It is indeed a heartbreaking act of desperation.
But why do they do this? It may be that evolution has presented this skink species with two options to weigh the costs of two scenarios. One option is to reluctantly fight the snake and fail, then watch the snake consume all her eggs. The other is to eat her eggs first, to conserve strength and energy for the next reproductive cycle.
To optimize the continuation of their species, the Long-Tailed Sun Skinks will choose the second option. They may despair and sacrifice their eggs, but they will not allow their offspring to fall prey to their enemies; they know they need energy to lay another batch of eggs.
“My home is too poor; I can’t feed that many mouths.”
Burying Beetle.
Burying Beetles say with tears in their eyes. This beetle is named for its habit of burying prey, often small mammals or birds, in the ground to create a nest for its soon-to-hatch larvae. This is a clever survival strategy, as right after laying eggs in the carcass, the newly hatched larvae will have immediate access to food.
The problem is that burying beetles often lay too many eggs, while the prey they find isn’t always large enough. There is a reason for this prolific laying. First, they can increase the survival rate when some of their eggs fail. Second, the more offspring that emerge, the higher their survival rate in the wild, facing predators or other mortality threats.
However, laying too many eggs can become a disaster if the larvae cannot find enough food in their early life stage. Competing for a limited food source can cause a significant number of burying beetle larvae to starve.
At this point, the mother beetles must take action, even while they are in labor and cannot go out to find more food. Evolution offers them a two-in-one solution: eat the late-developing eggs.
When a burying beetle notices that the number of larvae in the nest is too high, they will consume the slower-developing eggs. This behavior was documented by zoologists since 1980, but was studied in depth only in 2013.
It turns out that the late-hatching larvae of burying beetles are often weaker than those that hatch earlier. Therefore, this beetle species not only eliminates them to increase the survival chances of stronger siblings, but it also performs a “natural selection” behavior—albeit not quite natural—to help enhance the genetic quality of the species in future generations.
“They are sickly; I can’t let them suffer.”
It must be said that the Japanese Giant Salamander is an exemplary father. In this reptile species, the responsibility for caring for the eggs does not fall to the females but is entrusted to the males.
Japanese Giant Salamanders will care for their eggs and hatchlings for seven months, a considerably longer period compared to the maternal responsibilities of the Long-Tailed Sun Skink mentioned earlier, which only cares for her young for a week.
During these seven months, the salamander fathers take their responsibilities very seriously. They often use their tails to fan the water around the nest to provide oxygen for the eggs.
Importantly, these salamanders carefully clean their nests. They will remove any organic debris that may accidentally blow into the nest to prevent it from becoming a breeding ground for a highly dangerous pathogen for the eggs: fungi.
Adult salamanders are not adversely affected by fungal infections. However, their young can be. Fungal infections can kill juvenile salamanders, and fungi can spread very quickly in a newly laid nest.
Therefore, if the male salamanders finish cleaning the nest and somehow fungi still manage to grow and infect some of the eggs, the father salamander will consume those eggs. The aim is to protect the remaining eggs from fungal spread.
This behavior is referred to as “epidemiological cannibalism.” And it seems that this doesn’t stop at just eating eggs. Sometimes, male salamanders have been observed consuming juvenile salamanders that are too sick to recover.
It’s indeed a tough decision for the Japanese Giant Salamander.
“I don’t eat my young; they merely donate some of their blood to me.”
Dracula Ant.
While some species voraciously consume their eggs and young, there are others that simply bite their offspring without killing them. Take the Dracula Ant as an example; as the name suggests, they drink the blood of their young.
However, it’s not exactly blood. Like other insects, ants have hemolymph, a circulating fluid in their bodies that allows them to store water and essential nutrients for their activities. Some ant species have been observed sucking hemolymph from their larvae.
Adult ants, usually the queens, will suck hemolymph directly from the larvae by piercing their backs with their mandibles. Fortunately for the larvae, the wounds heal quickly without leaving any scars.
Interestingly, it seems evolution has equipped young Dracula Ants with the instinct to donate blood to their parents. From a young age, they develop small fissures on their backs, allowing adult ants to reach in with their mandibles. A gentle bite is all it takes for Dracula Ants to pierce the larvae’s back and suck their hemolymph.
Why do they do this? It turns out that ant colonies sometimes face starvation when workers cannot find food. At such times, each young larva is willing to sacrifice a bit of its hemolymph for the queen in the nest.
It seems that only the queen is permitted to suck the hemolymph from her offspring. And this act is only performed in dire situations. If worker ants are still able to bring food, they will never suck the hemolymph from their young.
Furthermore, the queen Dracula Ant will only suck hemolymph from the larvae if she counts enough larvae in the nest to sustain the population. If there are too few larvae, she would rather go hungry to allow the young to grow.
Therefore, this is not exactly an act of cannibalism; the larvae of the barred-chin blenny are merely sacrificing themselves for their mother and the bond of motherhood.
“Too Young to Be a Dad, I Just Want to Mate”
Barred-Chin Blenny.
This may be one of the most irresponsible and condemnable behaviors in the animal kingdom. The barred-chin blennies eat their offspring simply because they are eager to mate and do not want to raise their young until maturity.
Similar to the Japanese salamander, the responsibility of caring for the eggs and raising the young in barred-chin blennies is assigned to the males rather than the females. However, male barred-chin blennies are irresponsible fathers who prefer to have fun. They neither fan the water to supply oxygen to the nest nor hesitate to throw eggs out of the nest to avoid parental duties.
It turns out that in these fish species, there is a sex hormone called androgens. A male fish can only mate if it has a sufficient concentration of androgens in its body. In an experiment, scientists provided eggs to male barred-chin blennies that had not yet spawned. They observed a decrease in the levels of sex hormones in these fish, rendering them incapable of mating.
Conversely, if scientists remove the eggs from the nests of these male barred-chin blennies, the fish immediately increase their androgen levels and return to mating with females to produce a new brood. They accomplish this within just 24 hours.
This experiment explains why, in nature, barred-chin blennies are sometimes caught eating their own egg clutches. And if they do not eat them, they will still throw the eggs out of the nest to avoid fatherhood.
Scientists are still trying to find an explanation for this phenomenon. It seems illogical that barred-chin blennies invest so much time and energy into spawning, only to discard or consume their offspring.
One possible explanation is that when male barred-chin blennies find their clutch too small or of poor quality, they will destroy that entire brood to spawn a new one. Because if they do not discard the eggs, the concentration of androgens in their body will not be high enough to mate again.
Impatient male barred-chin blennies cannot wait for these weak eggs to mature into weak fish before returning to a single life to mate. They think life cycles are short, so it’s best to spawn a new clutch right away.
From a human perspective, we see this behavior as irresponsible, cruel, and condemnable. But perhaps, the very cruelty of the barred-chin blenny ensures the survival of their species, at least for the brood they choose not to consume.
