Is Styrofoam biodegradable?

The short answer is no. And since it's not and you find yourself saddled with styrofoam packaging try recycling it. If you're a gardener use it in pots as lightweight drainage and frost proofing. If you are artistic or a crafts person try modeling with it. It can be sculpted with a hot wire or tool, and painted (not with a solvent based paint). It can be used as insulation or offered to your local school for projects. As a last resort, try offering it on Freecycle or Freegle.