I get this too. They're often full circles of varying size. I have some by the gate, some around the lake, a whole bunch by Romeo and the cave area. They are starting to ruin the landscape for me especially at night because you can see them glowing bright white from a mile away.
I have not figured out how to get rid of them. I have tried using the axe, the sell gun, and eating them. If I start eating one at around 20 hunger, it will fill me up before I can finish. If i return later when hungry they seem to regenerate.