"A noiseless, patient spider" (line 1)
This is an easy one. First line, first image: all about nature. Well, maybe. Even though this poem definitely starts out in the natural world, there are already some hints that humans are here. For example, "patient" is definitely a word that you use to describe a human, or at least an animal with fewer than eight legs. To be patient, you sort of have to be capable of being impatient. And maybe spiders are, but we don’t know. Already, the natural images are mixed with human descriptions.
"On a little promontory it stood" (line 2)
The spider’s little perch is definitely a place in nature, but Whitman doesn’t say much about it. In some nature poems we might have green rolling hills, fluffy clouds, etc. Here, we don’t even find out if the promontory is dirt, grass, or rock. Whitman strips away most descriptions of the natural setting. He mostly seems interested in what this spider does, and how that compares to human life.
"It launched forth filament, filament, filament" (line 4)
For all the lack of information about the place, Whitman is pretty specific about this one thing which the spider does. He observes really closely, and, for a while, he sounds more like a scientist than a poet. The idea of men observing and learning from animals is a key theme here, and one of the big ways that man and the natural world tie together in this poem.