Cluster Flies
Pollenia spp.
Adult cluster fly with checkerboard pattern (Ryan Davis, Utah Sate University Extension)
Adult cluster fly (Tristram Brelstaff, Wikimedia Commons)
Yellow hairs on cluster fly (Ryan Davis, Utah State University Extension)
Identification
- dull grayish brown
- yellow hairs on the thorax
- slow moving; frequent at indoor windows in the winter
Nesting Habits
- adult flies lay eggs in soil and the maggots move to and develop on earthworms in fields and turf
- as many as four generations per growing season
- seek overwintering sites in buildings
- typically overwinter in upper levels of buildings (e.g., attics, wall voids, false ceilings)
Diet
- larvae (maggots) develop as parasites of earthworms
- not associated with garbage or animal wastes
- adults feed on flower nectar
Significance
- adults seek sheltered areas to overwinter such as crevices and cavities in buildings in late summer and early fall
- may become active during warm periods of winter
IPM Recommendations
- Monitor for cluster flies in the fall on the outside of buildings on sunny walls.
- Monitor for cluster flies in the winter on window sills.
- Caulk and seal exterior openings, cracks and crevices on building exterior.
- Keep screens in good repair.
- Vacuum flies.
- Use a fly swatter.