Olafactory Affinity Between Dogs and Earthworms

Okay, I'm pretty sure this isn't new news, but I've noticed that when our terrier/pappilon mix is outdoors and she finds the smallest remnant of a dead and dessicated earthworm - she just loves to roll and rub as much of her face and body on the earthworm remains as is possible. This is quite perplexing, since usually the remains of the earthworm on the sidewalk is usually more sidewalk concrete, than it still is anything resembling an earthworm.

I'm pretty in-tune with some of the innate behaviors of dogs and where those originate from, but the origins of this apparently compelling, innate behavior escapes me. Any insights?