Ants aren't interested in rolling down the highway, but when they've invaded your car, they can drive you batty every time you get behind the wheel, creating a hazardous distraction, especially if you're squeamish. You may need to use a combination of sanitation and bait as vehicle pest control -- revoking their license to operate there.
Watch where you park; chances are you're parking near an ant hill or a treed or bushy area where busy worker ants march, ever in search of food that's on or in anything, including your car. To an army of ants, your nearby vehicle containing stale fries, sandwich crumbs, dropped candies or sweet-smelling pop cups or juice boxes is like a welcoming food truck. Wherever you park, keep the windows closed to help restrict access.
Vacuuming your car is a good start, not just to remove many of the ants, but also the crumbs or food particles they're feeding on or taking home to their queen. Do a thorough job, getting in the seat crevices. Slide the seats backward and forward to get at the floor areas beneath. Washing the interior also helps. Focus on any sticky spills, which are like energizing nectar to an ant.
Bait and See
Vacuum the car every couple of days or as you see more ants inside. If this doesn't control persistent pests, try a non-toxic home remedy or two. Make sticky traps to set on the floor while the vehicle is parked; use double-sided tape on one side of a few floor-mat-sized-or-smaller cardboard squares. Alternatively, sprinkle the floor with some type of people-safe food product that repels or deters ants, such as black pepper; table salt; or crushed, dry mint leaves. Mint also acts as an automobile air freshener. Vacuum after a few days.
As a natural and relatively safe-to-humans extermination product, dust the floor trim along the entry points with a little diatomaceous earth. To remove the powder before driving, wipe it up with a damp rag, or use a shop vacuum -- the fine fossilized-algae particles damage the ants' exoskeletons but also can clog a standard vacuum cleaner's filter or even overheat the motor.
If natural fixes don't stop the invasion, set one or two ant bait stations in the car, but only if the manufacturer's label advises that it's safe to do so. If you plan to use bait, place the peel-and-use canisters near the doors, while the car is parked, and remove them before driving. If children or pets ride with you, do not use toxic bait.