📋 Steps
1
Identify blow flies vs house flies
Blow flies (bottle flies): 6-14mm; metallic blue, green, or bronze body — the metallic sheen is the key ID. Cluster flies: dull grey, no metallic sheen. House flies: grey, dull. If you have metallic-shiny flies, something is dead nearby.
2
Follow the flies
Blow flies emerge from the dead animal and fly toward light. Observe which window or light source they gather at most heavily — this often points toward the direction of the source within the wall or ceiling.
3
Inspect the attic
If flies are concentrated in a specific room and the attic is accessible, inspect for: dead squirrel, bird, or rat; a bat maternity colony that may have had die-off. Smell the attic — the odor is strong and localized near the source.
4
Check accessible wall voids
Remove outlet covers near the room with highest fly concentration. Smell and listen for fly activity inside the wall. A dead rodent in the wall produces flies for 7-21 days depending on temperature.
5
Remove if accessible; wait if not
If the dead animal is accessible: remove in sealed heavy bags; clean and disinfect; apply odor eliminator. If in an inaccessible wall: wait 2-3 weeks for the population to run its course — the odor and flies both subside as the animal desiccates.
💡 Tips
- The blow fly cycle is self-limiting — once all the larval food (animal tissue) is gone, the population collapses within 7-14 days even without treatment
- Fly strips and light traps provide relief during the emergence period without addressing the source
- In summer heat, a dead squirrel produces flies for about 7 days; in winter cold, the same animal produces flies for 3-4 weeks as the cooler temperature slows development