Go to a hardware store or a place such as home depot while it is.
Surge of flies on house siding.
It might be the warmth or something is on the siding that they are having for lunch.
Insects such as flies are naturally drawn to vinyl siding because vinyl siding attracts build up of airborne sugar particles from nearby trees plants and brush.
The most common reason for flies swarming all over your house is an infestation inside or nearby your home.
Some of the common flies found in houses can go from egg to adult in about a day in ideal conditions so even if you kill them or let them out this is probably how they are replenishing new ones are hatching.
I suspect they are not house flies at all maybe stone flies that are hatching off water or termite swarmers or boxelder bugs.
Take some sample flies to a local pest control company where they will identify the fly for free.
Not sure why they are there or where they are coming from.
Most types of house flies get a big yuck response.
You can try planting herbs and flowers such as basil or marigolds around the house or even plant a few.
Creating an evolutionary arms race that has gone on longer even than the existence of birds.
The source is likely inside your house garage attic or garden.
All have different treatments.
If i go outside they are clinging to the siding vinyl and buzzing around hitting me in the face.
I think a few even bit me it feels like.
Unlike brick or wood homes the sugar particles which may not be detectable to the human eye stick to the vinyl siding causing flies to gather.
Those large flies in your home in winter are probably cluster flies which overwinter in the protected areas between the inside and outside walls of your home or in the attic or basement.
If you suddenly see a swarm of flies that means dozens of eggs have already hatched and developed into flies.
Informally the term house fly often applies informally to any fly found inside the house and depending on the locations and situation a handful of fly families are happy to call.
Overwintering insects generally stay in secluded areas until the warming and lengthening days of spring pull them from hiding.
Once you know what it is then you can form a plan to get rid of them.
If it were me i d hose down the siding.
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The flies that have been chased by the fast sighted birds will be evolving faster reactions to get away.