Recommend a really good ant killer/bate trap.

[mistyoptic]

We've had them a couple of times in the kitchen.
Nippon ant killer has got rid of them within a couple of days. It's like a gel so easy to put in a milk bottle lid or similar to keep it away from food

Agreed. We put a couple of drops on an old plastic loyalty card near their route

 

[MidnightRider]

Difficult, but you really need to find the ingress point and block it. If you can't, then you will keep getting repeat problems each year and also risk poisoning all sorts of other creatures as you dont know where the poison will end up in the food chain or indeed in your room if it gets walked about by anything.

Might be worth checking outside to see if you can see an entry point. Watching the ants for a while can also help, as you will gradually see patterns of movement.

 

[Randomnerd]

Ants are the bottom of the food chain, and as such are very important.
Clean up all your crumbs.
Block up ways in.
Use white vinegar as your cleaning product on floors - this blocks an ant's pheromone path and they go elsewhere.
Poison is lazy, and, environmentally disastrous.