Remember sandtiger sharks? They eat their siblings…in utero. Why? Because they can—the embryos develop teeth and the ability to swim about halfway through gestation—and because eating their siblings helps them grow into big babies (and big babies don’t get eaten). This act of sibling rivalry is known as intrauterine cannibalism and it is certainly not the only kind of cannibalism in the animal kingdom.

There’s sexual cannibalism where one animal (often the female) eats its mate after—or during—mating:

Spiders do it. Male Australian redback spiders actually launch themselves into their mate’s jaws during mating. Standing on the female’s abdomen, the teeny tiny male inserts a palp (the spider equivalent of a “disco stick,” kind of) into one of his mate’s genital openings, and then catapults himself into the female’s mouth. She starts digesting him, but he escapes and puts his second palp in her second genital opening and vaults back into her mouth. This time, she gobbles him up.

Female garden orb-weaver spiders attack their mates right after mating begins, but garden orb-weaver males fight back by grabbing part of the female genitalia and holding on for dear life. Alas, it doesn’t work. The counter-attack buys the male a little extra time to maximize the amount of sperm he transfers to his mate, but the female still eats him—most of him, anyway. Some males leave pieces of their “copulatory organs” inside their mates.

Even though getting eaten sucks, sexual cannibalism is an advantage for male spiders. Usually, cannibalized males fertilize more eggs than uneaten males and they often prevent other males from fertilizing their mate’s eggs even after they’re dead. Sexual cannibalism isn’t quite as advantageous for male praying mantises. If a female praying mantis is hungry she will devour her mate. She bites his head off right away—an act that may accelerate sperm delivery—then finishes off the rest of his body. The only benefit to the dead male is that the female will be healthy enough to bear his brood.

…Filial cannibalism where parents eat their babies:

Burying beetle mothers feed their offspring by eating and regurgitating pieces of mouse carcass. Unfortunately, there’s rarely enough regurged mouse to go around. The mother feeds one baby, then the next and the next until she runs out of food. To the mama beetle, running out of food before she runs out of hungry babies is an obvious indication that she has too many babies. So she does what any mouse carcass-regurgitating mother would do: she eats the extra babies.

Some male freshwater fish eat their babies when they’re not really sure who the baby-daddy is. Typically, a male guards the eggs he has fertilized with a female, but sometimes a male is cuckolded by other males who sidle up and spawn with the female at the same time. Such cuckoldry leaves the egg-guarding male pretty friggin’ insecure about the paternity of “his” eggs. As a precaution, he eats them.

…and then there’s regular ol’ cannibalism:

Big hake (a deep sea fish) eat little hake. In fact, hake account for between 40 and 70 percent of the diet of hake. Why? Because it makes sense. Juvenile hake eat copepods, but chasing copepods requires more energy for an adult hake than the hake would get from the copepods. Instead, the big hake eats the copepod-eating little hake and gets all the nutritional value of the copepods and the fish.

Locusts also have a habit of munching on each other when food supplies are low. According to recent research, these cannibalistic tendencies may be the cause of mass locust migrations, also known as plagues. Hungry young locusts nip at other locusts’ abdomens. The victims take off to escape the cannibals. Other locusts, upon seeing the fleeing insects, scurry away before the cannibals start to nip on them. One thing leads to another, and before long all the locusts are on the move.