Nor Crystal Tears (Humanx Commonwealth, Book 3)

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 . . .