There are large composting worms that can be bred rather easily. European night crawlers and African night crawlers are 2 that I know of. They breed in warm temps and are easy to feed and culture. You can even gut gut load them in your bins by feeding mainly vegetable and fruit scraps instead of grain but I don't know if it would make much difference but I am definitely NOT an authority on that issue with worms or anything else when it comes to gut loading.