Flies Attack!

For the past 3 days, me and family have been kept busy with

getting rid of this!
We have no idea what fly is this.
They have been coming to our house flying here and there, stopping here and there.
It looks harmless and does not come disturb us, but the sight of it irritates me.
My mum has mastered the skill of 空中抓虫; whereas i have mastered the skill of smacking them down while they are flying then "kop" them in this container before throwing them out of the window.
While to.to has been excited with us chasing flies antics at home.
i believed this silly dog must have thought we are playing some games and he excitedly wants to participate.