The Dryad belongs to the oldest layer of Greek belief, a relic of an age when the divine was not found in marble temples but in the living world itself. The word dryas comes from drys, the Greek word for oak, and originally the Dryads were specifically the nymphs of oak trees. Over time, the term expanded to encompass all tree spirits, but the oak remained sacred above the rest, for it was the tree of Zeus, the king of the gods. In the rugged mountains of Arcadia, where the forests were dense and the cities few, the Dryads were most at home. They were shy creatures, rarely seen by mortal eyes, and many would reveal themselves only to Artemis, the virgin huntress goddess who roamed the wilderness with her bow and her hounds. A traveler who walked alone through an oak grove might catch a glimpse of a pale face among the leaves, or hear laughter that had no source, or feel the sudden certainty that the trees were watching. The Dryads did not seek human company, but they were not hostile. They were simply other, beings of a different rhythm, tied to the slow turning of seasons and the patient growth of wood.

The most profound distinction among the Dryads was between those who were spirits of the forest in general and those whose lives were bound to a single tree. The Hamadryads, whose name means "together with the tree," were born with their oak or poplar and would die when it fell. This was not metaphor. If a woodcutter's axe bit into the trunk of a Hamadryad's tree, the nymph felt the wound as her own. If the tree was felled, she perished with it, fading like smoke into the air. Because of this, the gods were fiercely protective of sacred groves. A mortal who cut down a tree without first offering libations and prayers to the nymph within risked divine punishment, and in some cities, the destruction of a sacred tree was treated as a crime against the gods themselves. The Greek geographer Pausanias records that in Arcadia, certain oak groves were so ancient and so holy that no one dared to enter them, for the Dryads within were known to be dangerous to intruders. The woodcutter's ritual was simple but essential: a prayer, a small offering of wine or honey, and a request for permission before the axe was raised.

The Dryads played a crucial role in the most important birth in Greek mythology. When Rhea, the Titan mother of Zeus, hid her infant son from his father Cronus on the island of Crete, she entrusted him to the care of nymphs. Among them were the Meliai, the ash-tree nymphs who had been born from the blood of the castrated sky-god Uranus when it fell upon the earth. The Meliai were the first tree spirits, ancient and powerful, and they tended the baby Zeus in the cave of Mount Dicte. They fed him on the milk of the goat Amalthea and on honeycomb, and they hung his cradle from a tree so that Cronus, searching the earth for his hidden son, would not find him in the ground. The Dryads of Crete, the Idaian nymphs of Mount Ida, also watched over the infant, dancing around him and clashing their cymbals to drown out the sound of his crying. Without the protection of the tree-nymphs, the king of the gods might never have survived his infancy, and the world would have remained under the tyranny of the Titans.

Not all encounters between Dryads and mortals were nurturing. The story of Erysichthon stands as the darkest warning against violating the sacred groves. Erysichthon was a prince of Thessaly, a man of monstrous arrogance who decided to build a banquet hall and needed timber. He came to a grove of Demeter, the goddess of grain and harvest, where the tallest and most ancient oak stood. The tree was known to be the home of a Hamadryad, and the local people had hung garlands and offerings upon its branches. Erysichthon laughed at their superstition. He seized an axe and struck the oak himself. The tree bled, and a voice cried out from the wound, the voice of the Hamadryad within, begging for mercy. Erysichthon struck again and again until the great tree fell, and the nymph died with it. Demeter, enraged by the murder of her grove's guardian, cursed the prince with an insatiable hunger. No matter how much Erysichthon ate, he starved. He consumed his own wealth, sold his daughter into slavery to buy food, and finally, in the last extremity of madness, devoured his own flesh. The Hamadryad's death had been avenged with a punishment that matched the crime: the destruction of the tree had brought the destruction of the man.

The Dryads endured in Greek culture long after the old religions faded. The poet Hesiod, in his Theogony, lists the Meliai among the first children of the blood of Uranus, giving them a genealogy as ancient as the gods themselves. The Roman poet Ovid, in his Metamorphoses, tells of how the Hamadryads wept when the musician Orpheus played his lyre, and how they emerged from their trees to listen to his song of loss and love. In the Dionysiaca of Nonnus, the Hamadryads dance in the army of Dionysus, the god of wine and ecstasy, their tree-bodies swaying to the music of flutes and drums. The philosopher Pliny the Elder wrote that in the old days, trees were believed to be so full of divine spirit that felling one was considered murder. Today, the word "dryad" has entered the vocabulary of fantasy and ecology alike, a name for the spirit of the forest that refuses to be forgotten. Every ancient oak that still stands in a European wood, every sacred grove that has escaped the axe, carries the memory of the nymph who was born with it, lived within it, and perhaps still watches from the shadows of its leaves.