You under the reason for the existence of ants?
Family opening my door, but not closing it the same way it was before. I often have my door almost closed, and I hate when its like that and they close it. And same for if it was closed and they leave it open when leaving my room. OCD.When my mom comes in my room while I'm asleep, whether it's at night or in the morning, and then leaves, if she closes the door to where it doesn't click into place and you can just push or pull it open, it annoys me. Our cats always know when the door is like that, so they'll just push it open and come in. My room's off-limits to cats, dogs, and people, after all.
The guy whose "brilliant" idea it was to breed bees and accidentally invent Africanized Bees. Great job, man. You created extremely hateful, super territorial, merciless murder bees who will send the whole darn hive after you and kill you.
Parasites. They actually have no purpose or use in the world, so why must they exist? I understand bees' existence. I understand ants' existence, as much as I hate ants. What's up with parasites, though, other than to make organisms suffer?
Tell me then.
Ants invade other, perfectly functioning ecosystems that don't have ants, and tear them apart. Animals have gone extinct because of ants
I tolerate vermin. I can't stand the large ones.
Lets say you've got a little tiny ant eating your leftover crumbs. Aww that's cute. But those gigantic ones the size of... of... a really big ant. KILL IT WITH FIRE!
Ants help decompose things, and they probably even eat vomit.
There are other creatures that tear up ecosystems simply because they somehow got there from another place. I think there's a town or state or something here in America where people had a pest problem so they imported a type of frog, and now those frogs have begun overrunning the place and throwing their ecosystem out of balance.
Africanized Bees are a huge problem, too, though that's mostly because they come at you with everything they've got just for so much as walking within several feet of their hive. So many of them sting you that they quickly inject enough venom to kill you.
There's an African rat beginning to invade America, as well, and it's huge. Seriously.. huge.
A man holding one of the rats I'm talking about
The reason the guy in that photo is wearing a mask is because they're at a mine field. The rats are actually useful in Africa, where they train them to detect mines without triggering explosions. But here in America, they cause trouble and scare the crud out of people.
tl;dr: A lot of species start causing trouble for an ecosystem when they've been transported there from somewhere else.
[Edit]: The rats are called giant pouched rat, and apparently they can also detect tuberculosis. Neat. How do you know you have one? Well, it's... giant... and most of its tail is black/gray, but the end is pink.