I am looking for a book that was bought at a school book sale in Massachusetts in the mid 60’s by a ninth grader. It’s about a group of men on a desert island with poisonous spiders or crabs. One man has immunity to them and becomes the leader. A black man also develops immunity and splits loyalty in the group. At that point in the story the book was stolen from my friend and he hasn’t read another book since. Thank you for any help.