Which of these flies does NOT transmit any human diseases?

The cluster fly is known to primarily be a nuisance pest. It is an occasional intruder in buildings, particularly during the fall when it seeks shelter from colder temperatures. Unlike some other fly species, cluster flies do not feed on human waste, decaying organic matter, or other substances that may harbor pathogens, which means they do not serve as vectors for diseases that could affect humans.

In contrast, the other flies mentioned, such as the house fly and blow fly, are known for their ability to transmit various pathogens due to their feeding habits and life cycles. For instance, house flies can carry bacteria, viruses, and parasites, and are often found in unsanitary conditions. Blow flies are also associated with decaying organic matter and can transmit diseases due to their habits. The phorid fly, while not as well-known, can also be linked to unsanitary conditions and may potentially spread some pathogens.

Thus, the cluster fly's specific behaviors and ecological niche make it distinct in that it does not pose a threat as a disease vector to humans, highlighting its lack of involvement in disease transmission.