An implied metaphor is a figure of speech that compares two unlike things without explicitly stating one is like the other, often suggesting a deeper connection.
In your list, "The ants are small soldiers marching" is an example of an implied metaphor because it suggests that the ants are similar to soldiers (in terms of their organized, marching behavior) without directly stating that the ants are soldiers.
So the correct answer is: The ants are small soldiers marching.