Why do dogs and cats always attack spiders?

My cats are always getting after all insects. I think it's part instinct and part " ooh look it moves, let's chase it and bat it around". They all have severe ADHD that is very obvious when things wiggle around.

It is just because they run - cats and dogs always chase anything that moves. By the way spiders do a lot of good catching bugs etc., I personally never kill them they are far too useful to have around.

Not all spiders are dangerous. I don't know why dogs and cats attack spiders.

Hunting practice. Cats have excellent vision to scan for moving things in the horizontal plain, and will pounce upon them.

Also, less than 1% of all spiders are harmful to humans. Many are beneficial - at keeping insects at bay from crops, for instance.

My entire family have always had animals and one of my uncles cats got bitten by a snake once (cost $1000 to make him better) then another of my uncles have lost a couple of dogs to snakes (but he lives out on a farm so it's kinda expected).

I think they do this to all insects and bugs, not spiders, especially. My cats do this to ants, and they're not typically dangerous (except some of those gnarly ones that live in the Amazon).

My cats never mess with spiders. They know better. But they love eating moths and then barfing them up on the carpet.

I once accidentally flicked a Huntsman spider onto my cat, and she flipped out. She ran in circles until it fell off her leg and then sprinted out of the room, and I didn't see her for hours.

Some spiders are deadly. It is actually natural for a person to urge to kill spiders.

The instinct to eat flesh is still in them, even if they do not learn the hunting behaviors. It is a game to try and figure out why they pounce so well.