cats seemingly kill birds and other wildlife for fun
(i love cats, before anyone gets upset)
Yeah, it's actually ecological terrorism to let a cat roam outside. "Domestic" cats have made several bird species go extinct. It's funny because I was going to post about cats being little sociopaths.
But that's hunting for sport. Those are it's natural prey.
Do cats kill other cats outside of a perceived threat to their life?
Hippos. They hate almost everything, but sometimes some of them hate each other more.
Some spiders tend to eat their partners, just because they're murderous, not hungry.
Different types of snakes tend to be quite racist and can't stand one another.
Koalas. They can be very aggressive about their leaves and will try to kick each other off trees.
Some sharks just don't give a shit on what they bite. Maybe because they're mostly blind.
Kangaroos will drown you, your kids, your pets and other kangaroos. Because fuck this, fuck that and fuck you. Kangaroos are psychos. Don't mess with them.
PS: Some of these examples might have specific circumstances or are plainly wrong. It happens.
The snake thing is from Rick and Morty, I'm pretty sure
Add dolphins to the list too. Not only killing for fun but also raping and getting high off other species.
I had no idea and decided to search around. While this may not directly answer your question, this article was a good read:
https://crimereads.com/the-most-murderous-mammals-adventures-from-the-dark-side-of-science/
Orcas. Orcas are menaces lol
Unsurprisingly, its Chimpanzees. I've once read about a case where researchers studied a certain group of chimps, and observed that from time to time a young would disappear from the group, never to be seen again. Turns out an older female was luring them away from the group and murdered them. Apparently, there is a non-interference rule in wildlife research, so this went on until the group simply died out, because every single young fell victim to the serial killer.
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