I’m a fan of live ladybugs for pranks. You can buy 1500 ladybugs for like $9. They’re intended for garden pest control. They come with some wet food inside the container, (which provides both food and water for them) so they can live in the container for a day or two after being delivered. And their instinct when you open the container is to fly away, because they naturally want to spread out and get away from where they hatched.

Quietly pop that lid open during a housewarming party, and they’ll be finding ladybugs everywhere for weeks. At most, they’re a minor annoyance. So it’s not explicitly harmful or destructive like some of the other options. If anything, they’ll actually help control more harmful pests.