Attack of the Vampire Worms (Ghosts of Fear Street #33) R.L. Stine

These worms want more than blood! When Jane and Lewis find themselves trapped underground, ghastly vampire worms lead them to a group of pale-colored strangers. 

The cave people claim they can't tolerate even the smallest amount of sunlight. Then Jane discovers that they've actually been horribly transformed... 

Now it's a race against time before Jane and Lewis become part of the cave family - FOREVER!