Small pyramid piles of soil appear during mid-summer.
Cause
Ants.
Harm
Ants in the lawn don't do any damage, although some varieties can bite!
Treatment
Chemical – if the ant hills are too numerous to ignore, find the nest – put out sugar and watch them come and get it and where they take it. Either sprinkle ant power around the nest site or make a break with a spade and sprinkle in the dust directly.
Organic - brush away the ant hills before mowing. Pour boiling water down into the nest.