Cleaning out the blocks themselves is optional. If you would like to, it can be done by removing the top and using any appropriate tool to clean out the groove. To further ensure they are sanitized, you can bake them at 200°F for 2 hours. If your nesting block attracted wasps, you should be aware that cleaning it may not be for the squeamish. You may find the remains of spiders or insects that the wasp left for its young, so be prepared for that! While it's common to hear concerns about diseases spreading in bees because of blocks that have not been cleaned out, this is often only true of bee homes with a high density of nesting sites, and our experience suggests that this is not a problem for low-density nesting sites like ours.