It depends on what part of the cave you’re talking about and where the cave is. Here in Gauteng Province, South Africa, near the entrance, you find a LOT of TRASH! People see a big hole in the ground and the first thing they seem to think is, “Ooooh! That would make a lovely place to dump my dirty diapers, beer bottles, old car parts, and dead animals!” Now, while this is really gross for cavers to deal with, a lot of animals that use the caves for shelter, find it positively delectable! This includes scavengers like hyenas and porcupines. You also find a lot of pigeons, owls, and weavers near our entrances.
As you get deeper in the cave, and farther from the entrance and sunlight, you find bats, cave crickets, and other creepy crawlies (but not always–some caves can seem kinda sterile, though it’s pretty dark, so who knows?). Unfortunately, for cavers, in SA, you find lot of “histo,” a fungus that grows in bat guano and bird poop. This nasty stuff also likes to take up residence in your lungs, so if you see this white, fluffy-looking stuff—-DON’T SNIFF!