Pranavore

Pranavores were a type of psi-form species that evolve on most planets with intelligent life and inhabit the psychosphere of the planet. They formed a symbiotic relationship with a particular intelligent species feeding off their excess positive emotions, such as excitement, and thereby protecting this species from sudden emotional outbursts.

Pranavores formed a hive mind and were placid in nature. Being psi-form creatures, they are usually invisible by their symbiotic partners. In exchange for excess positive emotions, they give back what is often described as "good vibes"

On Earth, at least two native species of Pranavores existed, one forming a symbiotic relationship with humans and the other with dolphins.

While meeting Gabby Gonzalez for the first time, the Tenth Doctor stated he only recently found out about them, decided to call them Pranavores and knew little about them. Using ocular circuits on a special headgear, he gave Gabby an opportunity to look at the human Pranavores, whom Gabby compared to butterflies.

Pranavores from an unnamed planet were experimented on by the Fleshkind in the hopes of creating a psychic weapon. This resulted in creating Cerebravores, who destroyed the Fleshkind and then attempted to invade Earth. (COMIC: Revolutions of Terror)

Behind the scenes
The name of the species means "feeding on ", in other words, feeding on life force.