Cluster Fly

Cluster flies do NOT pose a human health threat because they do not lay their eggs in human food. They are parasitic on earthworms and lay their eggs in earthworm burrows, where the larvae infest the worms themselves. They become a pest when they enter houses to over-winter. Large numbers of them can infest a home where they tend to gather in attics, wall voids and other cavaties. They can also be seen in large "clusters" in the high corners of unused rooms. They will also gather by windows in large numbers and are often easily identified by the loud buzzing noise and slow moving behavior.

Cluster fly activity can be found frequently in country houses, especially older ones that may not be sealed up as well as other houses. Activity is most prevlant in the fall but can be seen in spring as well when they become active after the winter. Infestations can also occur in areas where farm fields have been recently plowed. As earthworms become available, cluster fly activity will increase and if a farm house is nearby, they will often infest it if fall is near. Cluster flies are members of the same family as bottle and blow flies but have been seperated as their infestations and control methods are unique from the others.