I have 1"x2" plugs of dirt (hundreds) with perfect little holes to match, what is causing it and is it something to worry about?
The most likely culprit would be an animal, such as a raccoon, skunk or squirrel, either looking for grubs to eat or to dig up or bury food (in the case of squirrels). If you live in the city there are enough raccoons and squirrels to make a mess of your yard (that is, assuming there are no mischievous children around). If the holes are being dug up at night, the culprits are raccoons; if they are dug during the day, it’s most likely to be squirrels. There are groundhogs in the city, but they tend to make burrows.