@SplinterGroup they are decently heavy but not enough to contain unruly books.  If any of these books had a slouch, they would likely overpower the bookend.  They are better suited for small paperback books than the large ones in the photos.

@Pottz  They had a few live ones when I cut into them but then I put them in a toaster oven on 300 degrees for a few hours.  That took care of them.  I have  had a few of my larger creations let a few bugs loose though.