Pranavore

Pranavores were a type of psi-form species that evolved 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 were usually invisible to their symbiotic partners. In exchange for excess positive emotions, they gave back what was 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 one 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.

Human Pranavores helped Gabby and the Doctor defeat a party of these Cerebravores. They protected Gabby and the Doctor on the way to the Green-Wood Cemetery and, when the Doctor activated the empathic pulse, they both kept Cerebravores boxed in within the blast radius (COMIC: Revolutions of Terror) and provided positive energy to be boosted by the Doctor's empathic field amplifier. (COMIC: The Arts in Space)

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