When the boy is growing he has a wolf in his belly.

This is a traditional German proverb (Sprichwort) reflecting everyday domestic experience: adolescent boys, especially during growth spurts, often seem perpetually hungry. In German-speaking households the saying is used humorously—sometimes with mild exasperation—when a growing boy eats large portions or asks for food again soon after a meal. The “wolf” image draws on older European folklore in which wolves symbolize voracious appetite and untamed instinct, making it a vivid, memorable way to describe the sudden, intense hunger associated with puberty and rapid physical development.

The proverb means that a growing boy’s appetite can feel wild and insatiable, as if a predator were inside him demanding to be fed. Beyond literal hunger, the “wolf” can also suggest the restless energy and instinctual drives that accompany adolescence—growth is not only physical but also a period of heightened impulses. The saying normalizes this phase: the boy is not merely being greedy; his body is demanding fuel. Its tone is typically affectionate and comic, using animal imagery to make a common family reality easier to accept.