Beats me. I've seen an occasional one myself and wondered where the heck they were coming from. I get the tiny black ones. When I see them too frequently I use the Terro traps. Works for me. Right now I just dispose of the occasional one.

What is your general location? That information may help identify known localized pests. But to answer your other question.....ants can and will take up residence in the home to escape the cold, drought, excessive heat.

In my experience, freezing temps will make ants curl up and look like they died, but if you return them to above-freezing temps they get up and walk away. :p

Yes, the ants are probably living beneath the house or even somewhere in the house walls. They're so small that they can make tunnels and squeeze through to get inside to find food. If they are very small ants, and they're going for the dog's food, they are probably what's called 'grease ants'. Meaning they have a preference for foods with oil in them, rather than pure sugars.

Assuming they're grease ants, the easier and *SAFER* (less toxic than spraying!) way to try to rid your home of these ants is to make bait containing boric acid.

Here's a great article about identifying the ants and making a natural/homemade (safer) bait...

Here is a link that might be useful: Homemade ant baits

I had tiny ants a few weeks ago. We think they came in with firewood.
I mixed a bit of sugar & borax powder with water, put it in a plastic cap where the ants were. They come to feed, then die. I had to do this 3 different times. Haven't seen any for a few weeks.