Use undiluted car-washing soap (Mothers California Gold Carnauba Wash & Wax is safe for this process) to pretreat that bug graveyard before washing the whole car. You can use a 100%-cotton, microfiber or sponge applicator to wipe it on, or apply it with spray bottle (thinned enough so that it’ll squirt). It’s even okay to gently rub that soap into the offending stuck-ons with two or three fingers. Full-strength car soap will break down the dead bugs and tar without stripping wax or dulling paint.