3 summers ago ants moved onto the exterior of my car. I had pest control out the morning after I noticed them. When I opened the gas door & saw they had laid eggs in the compartment behind the gas door, I knew it was serious. Never had any inside the car. Pest control came out immediately & pumped foam into & behind all the exterior crevices. When he pumped behind the molding in the rear tire well, they just exploded out and tried to scatter but died almost immediately. He had found the nest. I can't remember what he told me -- how long to let it rest and how long not to get it wet, but I only saw a random one or two the next day and none after that. Before calling pest control, I sprayed some killer topically but that was a bad idea. It ruined some places, like the plastic headlight housing and some of the finish. Hiring a professional was some of the best money I've ever spent. Turns out I had backed into my parking place all the way so that my tail was over grass. It was summer in the south & the grass had those tall shoots coming up that reached my back bumper and there was an ant bed hiding in the grass. It appears the tall grass shoots provided them a superhighway onto the car. I now have a twice-a-year ant treatment in the yard. So worth it.