What is a characteristic behavioral trait of cluster flies?

Cluster flies are known for their tendency to congregate in wall voids, particularly in homes during the cooler months. This behavior is a survival strategy during the winter, where they seek warmth and shelter. Unlike some other flies, cluster flies do not typically swarm outdoors, as they are more inclined to remain close to their nesting or resting spots, particularly in buildings.

Additionally, the feeding habits of cluster flies involve parasitizing earthworms rather than consuming wood or living in water, which distinguishes them from other species. Understanding this characteristic of cluster flies is crucial for pest control operators as it helps in identifying infestations and implementing effective control measures.