flies from hell

[Eloisee]

Has anyone got any advice re my annual fly infestation? It has happened every year, last w/end of October, for the five years I have been living here. A huge swarm of tiny fruit-type flies appears from somewhere in the depths of my supposedly-sealed double glazed window units. They climb up the glass and over the ceiling. Not a huge problem, I spend the w/end hoovering them up.
However this year they were joined by a swarm of ladybirds (ok) and also a plague of big fat black buzzy jobs - definitely NOT ok, my flat resembled a Hitchcock movie set. Any ideas as to where these are coming from, how they get there, and most of all what can I do about it?
all suggestions gratefully considered
eloisee

 

[JohnD]

How old is your house, and who have you buried under the cellar floor?

 

[Eloisee]

1960's top floor of 10 storey block!

 

[RigidRaider]

These are cluster flies, a common problem.

See: http://www.the-piedpiper.co.uk/th6e.htm

Go out and buy a huge can of insecticide, spray the whole can everywhere they might be breeding then go out shopping.

 

[Eloisee]

wow - never heard of them before - your solution sounds good too!
many thanks rigidraider