What is the ecology of cluster flies?

The correct answer highlights that cluster flies are associated with earthworm parasites commonly found in the topsoil of pastures and turf. Cluster flies, specifically the species Pollenia rudis, are known for their unique behavior and life cycle, which involves laying their eggs in the soil where earthworms are present. The larvae then develop as parasites by feeding on the earthworms.

Understanding the ecological role of cluster flies is important because they contribute to nutrient cycling in the soil by their interactions with earthworms. This relationship illustrates a specific ecological niche that cluster flies occupy, differentiating them from other fly species that have different habitats or feeding habits.

In contrast, the other options do not accurately describe cluster flies. They do not exist in sewage environments, nor are they known to be earthworm parasites in any detrimental sense. They do not typically parasitize caterpillars, and while they may sometimes be found in moist environments, they do not feed on fungi. Thus, recognizing the correct ecological niche of cluster flies emphasizes their role in ecological interactions rather than misleading associations with other habitats or organisms.