What does it mean that the levee of a thousand miles collapses in the ant nest?

Destruction: destruction. Ant nest: an ant's cave.

A levee of a thousand miles is destroyed by an ant nest: it refers to an extremely long dam that will eventually be destroyed by the bite of a small ant. Metaphor means that not paying attention to small things will lead to catastrophe or serious losses.

The embankment of thousands of feet, collapsed in the ant nest; A room 100 feet high was burning with sudden smoke. -Han Fei's "Han Fei Yu Zi Lao" in the pre-Qin period.

Thousand-mile dike: the hole leaks, and the smoke from the house burns suddenly. -"Huainanzi Human Training"

A similar sentence:

Broken wood is born in the end; Nine-story platform, starting with tired soil; A journey of a thousand miles begins with a single step. -"Lao Zi" Chapter sixty-four

Therefore, you can't take Wan Li Road without accumulating steps; If you don't accumulate small streams, you won't be a river. Leap, not ten steps; This is a great contribution to the success of Ma Xu. Perseverance, rotten wood can't be carved; Perseverance, the stone can be carved.

-"Xunzi, Encourage Learning"