Could you please help me to identify these

[xenonk]

Hi All,
In my lawn these muddy small hills start appearing. They are not bigger than egg. And they're like coming out from the soil and get stick on grass and eventually kill all the green on that spot. I really appreciate if you can help, I'm totally rookie and my lawn will be all gone soon if I don't fight back with these.
They don't smell,
Here are the images:
http://aycu39.webshots.com/image/30278/2004591280627061538_rs.jpg (http://allyoucanupload.webshots.com/v/2004591280627061538)
http://aycu27.webshots.com/image/31426/2004570203772694995_rs.jpg (http://allyoucanupload.webshots.com/v/2004570203772694995)
http://aycu14.webshots.com/image/31893/2004595682438213149_rs.jpg (http://allyoucanupload.webshots.com/v/2004595682438213149)
http://aycu21.webshots.com/image/31700/2004502343665423426_rs.jpg (http://allyoucanupload.webshots.com/v/2004502343665423426)
http://aycu28.webshots.com/image/29467/2004526130493224414_rs.jpg (http://allyoucanupload.webshots.com/v/2004526130493224414)

Thanks,
Xenon

[Neil Bromhall]

They are caused by worms.
It means you have a healthy lawn with worms living under it. The worms help feed the lawn by dragging down leaf litter below ground.
These mud piles are what the worms have digested.
When dry they can be simply brushed, which breaks them up.