My brothers lawn has always had them and they are from red/yellow ants. They haven't caused any problems that I've seen and probably keep the grass nice and aerated.
Not problems as such but it's not nice when you accidentally kneel on one or accidentally scuff one with your foot as you're shuffling along on your knees doing hand weeding. Ants all over legs / in your shoe - yuck!
Heaven is ... sitting in the garden with a G&T and a cat while watching the sun go down
Apparently ant farmers commute to work. I wondered why I never noticed an ant best nearby. They also have ways of avoiding traffic jams by adjusting their speed.
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.