Lying around in the cavern are various small pebbles and dead insects. Other than that, nothing much.
The spider sees something on the other side; he begins to spin a web across the chasm. Within five minutes a webby bridge is formed. You poke him on to test it...
...his scream of "Aw crap! Nooooooo!" is heard fifteen minutes later. The spider had fallen through his own web and plummeted down. However, for some reason he falls back next to you.