I haven't fed bluebirds before, as I didn't have a ready source of meal worms, but I recently learned that bluebirds will accept the 4" X 4" blocks of suet (available at grocery stores and elsewhere) if the blocks are cut in half an laid flat on a platform feeder, rather than hung in the metal mesh cages that woodpeckers and other birds prefer. John Skaggs Powell, Knox Co. TN