Reply #2: That means you have or will have an infestation going soon

[ofrfxsk]

What you are seeing is swarming and there are many, many more that you don't see. You need to call an exterminator. There is a nest/colony somewhere near your house.
I have never understood why they congregate in bathtubs, showers whatever. That's where we first discovered ours. I thought they had gone away then a month later there were hundreds of them on the bathroom floor when I came home one day. Talk about a scream fest!
Just trust me and get an exterminator in there soon!