Plutarch's Natural Questions by Plutarch

Antipater in his History of Animals affirms, that she-wolves exclude forth their young ones about the time that mast trees shed their blossoms, for upon the taste thereof their wombs open; but if there be none of such blooms to be had, then their young die within the body and never come to light.

Moreover, he saith, those countries which bring not forth oaks and mast are never troubled nor spoiled with wolves.