There could be a nest inside the walls, or one positioned very close to an opening that might not be easy to find. It's probably not entirely INSIDE the house because they are clearly thriving and to do that, they need to get outside. Once you find the nest, you can get rid of it yourself using proper caution like any other nest.

But finding the nest? Might be challenging!Watch them outside and see if they go into any cracks or attic vents.

If it IS inside a wall or you can't find it or aren't comfortable dealing with it, it's probably worth bringing in a professional. They will know where to look.

Thanks Fori. I am trying to find out where they are coming from by myself first. I might end up calling pest control later. What are the methods that can tell me they are coming from inside the house and not come in from outside?

Most of them have to be getting outside to do their daily work--to eat, get food for the babies, etc. The ones that end up inside just screwed up and got lost. Because so many are coming inside, I'd be pretty confident that the nest is attached to the house in some way.

Do you have a lot of doors in your house or is it an open floorplan? If you can close every door in the house, you might be able to figure out which room they are coming into first and see if that offers any clues.

It's possible that this is a big nest and just can narrow it down by spending time outside staring at each part of your house and looking for wasp traffic.

If you can get someone to identify the particular species, you can then learn if they have preferred nesting locations and if you should be looking for a paper nest or a mud nest (or a hole in the ground). If you can get better photos--a closeup on wing veins is always nice--and tell approximately where you are located, it'll help get an ID. If you have a local extension service, you can probably bring them a corpse, but I'd call first. :)

Thanks for the hint. The pattern is that every morning around 11am to 2pm when it is warm I see the wasps on the window. I killed them all. The rest of the day has noting there. I observed few of them flying outside of the house and some stuck between screen window and glass window.

In your theory, if the nest is inside the house and some of them need to go out for work, what I see makes sense. If I don't kill them, let them to stay and watch where them go after sun down, will they go back to nest or not? If yes I might be able to find out where the nest is (inside the house). I will do it tomorrow instead of killing them.

I will also bring one to local pest control office to check the spices. Most of these pest control program is just lay down chemicals and not trace the nest if it is inside the wall or somewhat attache to the house. I will try my best to find it our before calling pro.

One another question - there are some ultrasound insect (wasp) repellent device that sounds pretty good. Would it help?

Thanks a lot!

After checking around the house I discovered there is a gap along chimney and I do see insects flying in and out. That means there is highly possible there is a nest inside the wall somewhere. Called local pest control service and they said they can treat it without opening the wall. Not sure if it is worth to do DIY first. Someone says the insect is Yellow Jacket and someone says it is Wasp. But I think the treatment is the same.

My only question is that does Pest Control company will seal the gaps by caulking or I will (have someone) do it myself?

New to these things..