What kind of larvae are these. Lots of them in the basement in the summer, crawling around on the floor and the walls
Those are not larvae, but adult millipedes. Myriopoda, Diplopoda. https://en.wikipedia.org/wiki/Millipede
Here is a good link from the U of Minnesota on common arthropods in the basement.
https://extension.umn.edu/insect-relatives/sowbugs-millipedes-and-centipedes