a literary work<span> dealing with shepherds or rural life in a usually artificial manner and typically drawing a contrast between the innocence and serenity of the simple life and the misery and corruption of city and especially court life</span>
Here it refers to the insect or earthworm that moves through the green grass.
I'm assuming that the answer is blanket because fog is often said to "cover the land like a blanket". May I ask what poem you are referring to? This would aid in answering the question. <span />