Harry Harrison's Deathworld 2 (The Deathworld Series)

On the planet Pyrrus, human colonists have fought a centuries-old war with the native life forms. These life forms adapt to human tactics and technology, evolving new species so rapidly that natives returning from even brief trips off planet must be carried in protective armor canisters from their ship to the safe buildings, where they will learn of the latest deadly threats. The Ethical Engineer is the second volume in the Deathworld series. It was originally published as a two-part serial in Analog magazine in 1963.