My old truck had an infestation of them. If it was sitting in the sun with the windows up there would be at least a hundred, many dead but many still alive. That residual smell lingered. I would vacuum them out regularly. I discovered that they were primarily coming in through an inlet duct for the AC that was breached in the firewall. I used an ozone generator in it to remove the smell.
I have a car that sits in the garage all windows up and AC off that inevitably accumulates 3 or 4 in it within a week. I don’t know how they get in. Yes they are a pita.