How can I store an open bag of dog food so ants don't get in?

I would throw the dog food away. Unfortunate that it wasn't in a sealed container especially since it's expensive dog food. Lesson learned. Sometimes that's hard to take.

Just guessing that the ants in the food will leave the bag and return to their nest. You just have to find a way to keep new ones from entering the bag. Maybe move the bag often. Spray their trail in but don't spray it near the bag.

Judith: If you suspect the ants came WITH the dog food, you can take it back to the store. Otherwise, it's best to throw it out...

Start with a fresh bag and put into a sealed container.

Dump the food, nothing you can do will be safe. Not worth the vet bills and illness inflicted upon the dog. Expensive to replace dog food, but the alternative is far more costly.

I use an old Christmas popcorn container for pet food. You can read about it here... https://www.homeroad.net/2018/01/recycled-dry-dog-food-container.html

I would throw it out. I wouldnt want to eat buggy food.

Ants indicate that your expensive dog food is full of sugar, either by way of sugar itself or high glycemic foods such as rice, potatoes, yams, etc. Our vet advised us to keep kibble in its own bag, after 7 days mold can grow if exposed to the air. We just feed our dogs a balanced raw diet now. They are so much healthier now.