I observed two different caterpillars being attacked this week!
First I saw an Aerial Yellowjacket (Dolichovespula arenaria) attacking a green caterpillar.
Then, on September 17, I noticed a spider running circles around a brown caterpillar, presumably trying to wrap it up in web.
Occasionally the spider would come and and try to bite the caterpillar, which would turn and twist its body, at which point the spider would go back to running circles...