I live in a small 141-year-old house. Upstairs, the floors are wide wood planks with large gaps in between them, that range from 1/8" to 1/2" (even in the summer with no AC). There is subfloor beneath.

Dust and dirt accumulate in these gaps, and it seems every time I drop an earring or something small, it seems to land in the gaps. Although I am tempted to just lay carpet and call it a day, I want to find something to fill the gaps.

I'm thinking something flexible. Caulk? If so, what kind? Has anyone had luck successfully filling the gaps and what did you use?