What about if the PC find the bugs in some loot? maybe an ancient treasure form a lost port, maybe a burial chamber. They could see that a plague is developing wherever they go, but not know why or how, this could be through rumors and at every tavern, they would hear that the last place they visited has been quarantined because of a mysterious plague!
Perhaps the eggs only kill when they hatch, and one of them is infected, giving them very little time to get to Marlifus... Go to Comment
Gives it an almost Alien movie type surroundings. The cocoons could be skattered all over and not much is remarked about them at first till they get deeper inside. Maybe the cocoon stages make them resistant to most weapons so they can't get inside them at first to see what they actually are. They never knowing what they really are until they start hatching. By then they are already deep inside the catacombs and must go back past all the now hatching cocoons to escape. Go to Comment
Horror to comic?
...one deicides to cut through the cocoon. A scary slimy monster emerges, its mind altered. In a coarse voice it screams: Mhummyyy? And lovingly envelopes its new mamma with its tentacles.
Comic to horror again?
Baby is hungry, and not above consuming your friends. OK, heavily inspired by Alien... Go to Comment
The PCs encounter an elaborate trap room, designed to fill with water, drowning those inside. Clever and resourceful, they disable the trap and move on.
Only later do they discover that this room is part of the elaborate cooling system that prevents beasts of elemental fire from overrunning the complex. While the fiery beasts run rampant, they begin setting fires, which causes the complex to become increasingly hot and smoke-filled. Additionally, the PCs now have to fight their way out past aggressive fire creatures...