Origin of Species, by Charles Darwin

Chapter VIII:
Instinct

Instincts comparable with habits, but different in their origin — Instincts graduated—Aphides and ants—Instincts variable — Domestic instincts, their origin — Natural instincts of the cuckoo, molothrus, ostrich, and parasitic bees — Slave-making ants — Hive-bee, its cell-making instinct — Changes of instinct and structure not necessarily simultaneous — Difficulties of the theory of the Natural Selection of instincts — Neuter or sterile insects — Summary.