Can anyone tell me what these are? They started out as a small area in one corner of my yard but have spread to cover half the yard within a week. I'm in Northern VA right outside of DC.

Earthworm castings.
Good for soil !👍👍👍
😎😎😎

They look like crayfish chimneys to me. Is it a damp area?

Thanks for the info, and quick reply! I have a grub problem every year so I was going to put down some Grub-Ex today. Is this a good idea if the earthworm castings are good for the soil?

My guess is that it is a miner bee or some sort of wasp nests.

Many bees nest in the ground: https://www.ces.ncsu.edu/depts...

Images of nest mound entrances:
https://www.bing.com/images/se...
https://www.bing.com/images/se...

Cicada wasps nest in the ground too; last year we had many sand Cicada wasps and mounds all over our lawn but their entrance holes are larger than the ones that ground bees make.

Worm casts for me as well. Think carefully before you put anything in the area as there are lots of beneficial insects etc in your lawn as well as some pests.

Thanks all for the replies; I appreciate it.

I believe they are ant hills. Note the hole in the middle of the mounds and compare with these pictures:

http://extensionpublications.u...

We've had holes like those on our land. They were ants, but I'm not sure which species they are.