What does Macbeth mean by "the worm that’s fled / Hath nature that in time will venom breed”?

Fleance will likely die soon from his injuries.
Fleance might attack when Macbeth least expects it.
Fleance likely inherited his villainous ways from his father.
Fleance may become a true threat to Macbeth as he ages.

[Macbeth.] the worm that’s fled
Hath nature that in time will venom breed,
No teeth for the present. Get thee gone; to-morrow
We’ll hear ourselves again.