Bay leaves are not poisonous -- if they were, you would not be cooking with them! The reason why you must always pick them out of the dish you are cooking before serving it is that the leaves do not become tender with cooking. They are thin, rigid, and have very sharp edges. If you accidentally ate one, it might lodge in your throat and choke you. Always count the number of bay leaves you put in a dish and make sure you take the same number back out again. Alternatively (and to help make sure you don't accidentally lose broken leaf bits) you can wrap the bay leaves and other spices (like peppercorns) in a bit of clean cheesecloth. Tie it off with cooking twine, put it in the pot, and attach the other end of the string to one of the handles on your pot to make it easy to fish out later.

To certain insects they are

They are in stews to flavor, but you take them out when the stew is done. I'm not sure if they are poisonous, but you don't eat them.