I like scorpions because they’re basically always a threat. The Giant Scorpion entry in the Pathfinder Bestiary offers scorpions ranging from CR 1/4 to CR 15—that covers most of your adventuring career. The Bestiary 3 is nice enough to save you some number crunching by serving up two of those vermin fully statted: the deadfall scorpion and the ghost scorpion.
As part of his meditations, a lama spends part of every day constructing a mandala out of colored sand. Seeking to have him killed, his political rivals send a shipment of large clay vessels filled with the expensive sand as a gift. When the jars are unsealed during the day, all is well, but that night nocturnal ghost scorpions erupt out of the sand to hunt. Fortunately, they strike while the lama is holding a clandestine meeting with a group of adventurers.
Deadfall scorpions are mostly found in old growth forests. But some varieties are aquatic. They hide amid the bayous, mangrove swamps, and even the occasional coral reef, often drowning their victims as they pull them underwater. Gripplis sometimes make armor out of their chitin.
“Only ghosts tread on the Path of the Pharaoh.” So says the papyrus warning tomb raiders away from the necropolis. But it is as much a clue as it is a warning: The “ghosts” in question are translucent ghost scorpions.
—Pathfinder Bestiary 3 237
We looked at another deadfall scorpion adventure seed back in our Giant Scorpion entry.