On a book shelf the first page of the first volume is on the "inside"
_ _
B| | | |F A|1 |...........................|10|R C| | | |O K| | | |N
| | | |T
so the bookworm eats only through the cover of the first volume, then 8 times 1000 pages of Volumes 2 - 9, then through the cover to the 1st page of Vol 10. He eats 8,000 pages.
If the bookworm ate the first page and the last page, it ate 8,004 pages.