JR in Nova Scotia has a crack between the slab of his garage floor and the foundation of the house, through which bugs are crawling in. How to seal it.
The crack was probably caused by normal shrinkage of the slab after it was poured. The best way to seal the joint with the wall is with something permanent but flexible. I recommend PL Polyurethane or Butyl sealant, easy to locate caulkings. If the crack is too narrow to be able to force caulking into the crack, you can now get DIY polyurethane injection kits.