...Ignoring the issues:
- Spider Mummy [Disease - Infestation of Maggots]
A. who would mummify a spider?
B. can a spider even be mummified?
Mummification precludes the presence of maggots.
Furthermore, maggots have medicinal uses, they can and are sometimes used in modern medicine to remove necrotic tissue from wounds. Yes, I am defending the honor of maggots.
A. Some interesting sub-culture that reveres spiders. One we've not seen before. That's why it's different.
B. (From the Monster Manual) -- Mummies defend tombs and other sacred places against intrusion, striking down foes with a deadly rotting disease.
This is a fantasy game. Infestation of Maggots is listed as a Druid spell. And so for variety, instead of Mummy Rot, I put that spell description there. Most diseases in RPGs are handled with similar effects or state changes. It was just something different, that's all.