Which fly is primarily a pest in rural areas due to its breeding habits?

The Face Fly is primarily a pest in rural areas due to its breeding habits, which are closely associated with livestock. These flies breed in the manure of cattle and can thrive in agricultural settings where animal waste is present. This environment not only provides a suitable breeding ground but also facilitates the fly's presence in higher numbers.

Face Flies are known for their role in transmitting diseases to livestock and humans, which further underscores their pest status in rural settings. Their breeding habits are particularly adapted to exploit the resources found in these areas, making them a significant concern for farmers and ranchers.

In contrast, the other flies mentioned have different breeding preferences that do not align specifically with rural agricultural conditions. For example, the Fungus Fly thrives in decaying organic matter and damp environments often found in urban settings; the Fruit Fly is primarily associated with decaying fruits and vegetables, commonly found in residential areas; and the Cluster Fly typically breeds in the soil of gardens and lawns, often seeking shelter in homes for winter. These distinctions highlight why the Face Fly is the correct answer for this specific context.