if they are crawling across porch diatomacious earth (sp) will cut them up.
I've recently started using DE around my vegetable garden and house for ants. Just a note to anyone thinking about using this stuff. DON'T buy the DE for pool filters. Buy the stuff that is for insect control.
Pool filter DE is mainly crystalline silica = BAD to breathe in.
Regular DE for insect control is mainly amorphous silica = Not as bad, but don't breathe it if possible.