Adventure Design

Casting a Rare Monster – The Festering Locusts of Fenmore

June 23, 2021

Last month I asked Call of Cthulhu fans for suggestions of rare monsters. I wanted to know which Lovecraftian monsters had rarely, if ever, appeared in a scenario. My challenge to myself was to write an adventure based around an obscure monster I had never heard of.

I received lots of suggestions. The Hounds of Tindalos were mentioned several times (which surprised me), Colours from Outer Space were called out as frequently MIA, and even Cthulhu himself was said to be a rare occurrence. Unsurprisingly, no one volunteered Deep Ones…

An Insect of Shaggai

One particular fan shook his fists towards the stars and mentioned the Insects of Shaggai were almost never seen. I wasn’t really familiar with these strange alien insects, who appear only a few times in some of Ramsay Campbell’s spinoff stories. Intrigued by the mysterious bugs, I tracked down a copy of the original short story and was left scratching my head.

For those of you not familiar with the Campbell story, the protagonist stumbles upon a strange, buried pyramid in the woods. He climbs inside and is immediately possessed by one of the Insects that live inside. The Insect uploads a database of alien history into the man’s head, which horrifies and befuddles him. In true Lovecraft fashion, he vows to kill himself before the story’s end.

So why haven’t the Insects of Shaggai been popular opponents in RPG adventures? On the plus side, they have some fantastic elements of body horror about them. Not unlike xenomorphs, they look for human hosts, embed themselves inside your brain, and then wait until dark to do something horrible with you. That’s great horror material!

On the flip side, while the insects are intelligent and devious, they don’t really seem to have a clear motivation or plan. And they’re kind of pathetic. They are stuck on Earth, and they don’t ever really leave their home. Their tech is all broken, their only allies are dumb, carnivorous trees, and the one thing their backstory makes clear is that they’re being chased around the galaxy by elder things worse than them.

Undeterred by their flaws, I made the Insects of Shaggai a key part of this month’s free adventure, The Festering Locusts of Fenmore. In this adventure, the PCs are colonials eking out a living in the vast, war-torn wilderness of New York. When a friend asks them to visit his loner father and evacuate him south, the PCs soon find themselves caught up in the man’s dark secrets. (If you’re looking for Lovecraftian horror through the lens of The Last of the Mohicans, this adventure may be up your alley…)

When you’re basing an entire adventure around a monsters, there’s a few guidelines to follow:

1758 New York is lonely…
  • Pair the Setting with the Monster. I liked that the original short story had the Insects stranded in a remote part of the country. When a monster can possess you and enslave you, there’s more horror to being alone in the wilderness with no hope for miles. To really embrace this, I set the adventure in 1758, in the wilderness of upstate New York during the French & Indian War. In this place and time, there’s nobody here to aid the investigators. There’s no police, no libraries, no help. Even the forts that dot the wilderness have no time for you – they’re fighting a war on all sides. Deal with your own brain bug.
  • Don’t Introduce the Monster Right Away. RPG players are incredibly effective at identifying monsters, finding their weaknesses, and then efficiently killing them. If you’re going to base an adventure around a single monster, don’t introduce it until at least the halfway point. Build tension and keep your players in the dark on what, exactly, they’re facing, until the last possible minute.
  • Always Tweak the Monster! Even if you’re using a rare monster from a hard-to-find 1964 short story, I guarantee one of your players will have heard of it! And even the best roleplayers will struggle not to bring their real-world knowledge to bear. (Cue Jurassic Park‘s “I know this!” scene.) GMs have a duty to tweak the monster so ensure that there’s a surprise waiting for even the most knowledgeable players. In The Festering Locusts of Fenmore, I ignored the fact that the fiction implies that the Insects only fully control people at night. While I keep the effect stronger at night, any player who happily crows that the bugs can’t get to him in the morning will be very wrong…

Get the Adventure

Download the free adventure, The Festering Locusts of Fenmore here:





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What are some of your favorite, unusual RPG monsters? Have you ever run or played in an adventure that starred them? Let me know in the comments below.

Related: Lovecraft in the Ice Age

Only registered users can comment.

  1. I like the Vashta Nerrada from Doctor Who, but that’s more of a trap than a monster by most game mechanics.

    Dust Devil, while an intelligent monster who usually takes the form of a man, would make for a great adventure.

  2. The tactical map included in the Fantasy Grounds download seems to be incomplete, especially when compared to the other maps that are included. it basically has a triangle, and a purple rectangle on it?

    1. Hmmm, this was fan created by Olympus RPG Group and I don’t use Fantasy Grounds, so I’m not entirely sure how to fix it.

  3. I ran this as a solo game (selectively reading the text). Concluding that Enoch was delirious from the infected wound, my character set out to find herbs in the area that might reduce fever. Upon passing the tree, he was swallowed and reduced to a pile of poop.

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