Merseyside,
United Kingdom 
what causes tiny mounds of soil on the lawn
8 Oct, 2010
Answers
at this time of year the worms seem to be the most active. so that would be my best guess.
8 Oct, 2010
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certain insect & earth worms, if really small could be solitary bees/wasps, all harmless I might add but without seeing a photo it's a little vague to be accurate. Intrigued to know.
8 Oct, 2010