I'm looking for a way to recycle biodegradable plastics myself and I was thinking about putting them in my wormery. Does anyone have experience with vermicomposting biodegradable plastics? Is it safe for the worms? Are there things to look out for?
The general rule of thumb that I have heard is no. I can't seem to find a good resource at this time that breaks it out conclusively, but the logic that I have heard goes as follows.
Composting happens at different speeds and different heat levels. Your typical worm bin tends to operate at a low temperature (otherwise the worms would bake!). This would be slower normally, but the worms speed up the process.
As the overall heat increases (usually as a result of the proper mix of materials and frequent turning), the speed of the material breakdown increases. (For example a commercial system like this - http://www.hotrotsolutions.com/ - can yield compost in as little as 10-14 days according to their site.)
Generally, you need a hotter, more active system to really break down a lot of biodegradable plastics. Not that they won't eventually break down in your regular compost systems, but they likely won't break down as quickly as the other materials, leaving plastic pieces mixed in the compost.
The other consideration would be whether this adds any value to the worms. I have found vermicomposting to be like raising a pet, allows having to make sure that they have the right amount of food and water. Much of the material that you put in the system breaks down quickly because the worms are either eating it or using it as bedding. I guess that the plastic could be a form of bedding (this is pure speculation) but because I would assume that it would break down much slower than the newspaper that it more commonly used, it is likely to end up gumming up your system.
It isn't a good idea to do so, the material from the plastic will build up in the worms bodies, and they will probably die. Also the compost could be toxic to the plants you are using it for.