Feeders are creatures of The Void who are prevalent in the Word/Void trilogy. Their specific purpose is never clearly defined in the series, though what they do and how they effect people is demonstrated. They feed on the energy of extreme emotions, particularly dark emotions.
Feeders are described as:
|“||Shadowy creatures that lurked on the edges of people's lives, feeders lapped up the energy given off by the expenditure of emotions. The darker and stronger the emotions, the greater the number of feeders who gathered to feast. Parasitic beings who responded to their instincts, they did not judge and they did not make choices. Most humans never saw them, except when death came violently and unexpectedly, and they were the last image to register before the lights went out for good. Only those like Nest, who were born with magic themselves, knew there were feeders out there.||„|
-- Angel Fire East (1999), pp. 41-42