Signs
for House Fly
The clearest sign is the flies themselves, especially clusters resting on walls, windows, and food. A more diagnostic clue is the dark "fly specks" scattered on surfaces, which are the insects' droppings. Pale maggots in nearby garbage, manure, or rotting matter point to an active breeding source. Source: https://extension.psu.edu/house-flies Source: https://entnemdept.ufl.edu/projex/gallery/dl/Beneficial_Arthropods_Parasitoids/TEXT/DIP_House_fly_Musca_domestica.html