I've heard of people putting them in the bottom of their pots for drainage and to make the pots lighter. I can't imagine them being used for plugs. Try a few just to see if they work!

That's funny Karyn! Like you, I had no idea there was biodegradable styrofoam. Good luck with your seeds!

Also, aside from being utterly non-organic (this is me saying they are manufactured from petroleum products, not that they don't contain carbon ;). Vermiculite is a natural mineral, altered in physical structure by heat, but otherwise perfectly normal... I'm not uncomfortable about having it, in small, loose particle form, around things I am going to eat, (it is a major component of the soil and rocks where I grew up) I can't say that about Styrofoam. Aside from being nearly worthless for the intended purpose of vermiculite, they will rise and float to the top in a way that will put even perlite to shame.

I'm reviving this incredibly old topic to report that I have added some cornstarch packing peanuts to my worm bin, and the worms LOVE!!! them. I added just a few at a time to the top of the bedding around the edges, where they would get damp but not dissolve completely right away, and they are attracting clumps of happy worms. The worms stitch themselves right through the peanuts once they get soft enough. Worm also love corrugated cardboard because the layers are glued together with cornstarch glue. It almost seems like the worms eat the starch itself rather than waiting for other small organisms to grow on it and eating them - but I think it's just that cornstarch supports such incredibly rapid growth of organisms, once it gets wet, that the table is set for the worms right away.