What about a Creepy Crawly Icky Sicky party? You could make a big cake that is in a flowerpot, with the icing coated with crushed Oreos and gummy worms. Party activities could include making goo (which the kids could take home in those cheap little plastic containers) or playing What's that Thing? (put stuff like sandpaper, cold noodles, a wet sponge, etc. in a paper bag, have kids feel around, and guess what it is.