Explanation:

- The passage describes the vision and sensory capabilities of ants.

- Blank 5: The sentence discusses how ants rely more on their senses and information from their legs and antennae compared to their vision.

- Correct Answer: "than" is the appropriate word here because it is used to make comparisons.

- Option 1 (than): Correct - compares two different sources of sensory information (legs and antennae vs. eyes).

- Option 2 (when): Would indicate a time reference, which is not contextually relevant here.

- Option 3 (then): Implies a sequence of events, which is not applicable.

- Option 4 (thus): Implies a consequence or result, which doesn't fit the comparison context.