Nor Crystal Tears (Humanx Commonwealth #9) by Alan Dean Foster - Vintage Paperback

Before Man and insectlike Thranx had become allies, when the reptilian AAnn were just occasional raiders of Thranx colony worlds, one young Thranx agricultural expert lived a life of quiet desperation.

A dreamer in a world of sensible, stable beings, Ryo buried himself in his work-reclaiming marshland from a tenacious jungle-until he came across a letter describing a relative's encounter with horrid, two-legged, soft-skinned space-going beasts...