One of the indications that your Crawlspace is suffering from water intrusion and increased relative humidity is mold growth. Mold grows quickly on organic surfaces like wood and growth can be explosive!
Here, you can see that the mold growth has actually started growing on every surface.
One of the side effects of mold growth is the stinky, rotting smelly that mold produces. If you smell your crawlspace, it's time for a vapor barrier!
Here you can see the old plastic vapor barrier, which has rolled away from the walls.
You can see in this case that the mold has compromised the structural integrity of the joist to the point that it will need to be replaced,.
One draw back of a dark, damp space isn't just mold. Critters are drawn to moist areas too.
Here's an overview of the crawlspace and it's pretty typical of most crawlspaces in the area.
Does this look familiar? Dirt crawlspaces can be a breeding ground for mold and fungus. Here is a guide to mold and causes for concern in your crawlspace.