[RckyRaCoCo]

An apartment I lived in(CA)was like that. One minute nothing, a little while later hundreds of ants in a line, either in the kitchen or bathroom. One time I killed a whole bunch but didn’t have time to clean-up the carnage as I was off to work. When I got home they were all gone.

[SamAdams76]

Ants have trails - sort of like highways - that they travel by smell. If you run your finger across their trail, you remove the smell and the ants coming up to it get confused and start jerking back and forth sideways looking to pick up the smell the trail.

After a period of time, they are able to figure it out and re-establish the trail.