“The great hulk of the scaled beast lay wheezing before me, and I am not ashamed to say that I was frightened: though it was injured, I knew the dragon could easily tear me in twain. The young monk, however, knelt beside the creature’s head, whispering to it in a strange growling tongue. I questioned the woman, but she ignored me completely, engrossed in examining the scaly monster. After much badgering, she said merely, ‘I do not mean to be rude, but you are quite a distraction. Please, leave me to my work.’” -Jeron’s Great Journeys, Book III, Chapter 4
On a location with numerous webs, and at least one big spider, there is a something inside a cocoon. It is humanoid in shape, still moving. If the heroes free it (not before they kill or drive away the spiders), they meet a ... zombie!
The poor zombie wandered the dungeon alone, and tried to kill a big living creature (= a spider). The spider used the usual treatment, even if this victim did not look tasty. The zombie can be easily killed as any other zombie. It got but several doses of spider-poison, so can be something worth if it is extracted. You can mention to a druid or ranger the fact the spider had no poison anymore.