Bloodchild by Octavia E. Butler

Years ago a group known as the Terrans left Earth in search of a life free of persecution. Now they live alongside the Tlic, an alien race who face extinction; their only chance of survival is to plant their larvae inside the bodies of the humans.

When Gan, a young, boy, is chosen as a carrier of Tlic eggs, he faces an impossible dilemma: can he really help the species he has grown up with, even if it means sacrificing his own life?