The other side of the book had this peculiar title. It could be confusing today, since people don't get the willies like they used to.
From the description:
With self-confidence as his only weapon, Leeming had only two choices: give in to the enemy and be captured… or quick-talk them into a real case of THE SPACE WILLIES!
The alien in the middle looks as if he already has one willy, if not more.