The nestbuilders are a spacefaring species native to the Milky Way. They are an extremely secretive species, hiding in interstellar space in order to evade the attention of the Inhibitors.
Fragments of destroyed nestbuilder ship were known to wash ashore on the Pattern Juggler-inhabited planet Ararat. These pieces resembled enormous shells produced by aquatic organisms, and as a result the colonists referred to the unknown objects as "conch material."
The nestbuilders are not themselves intelligent, having long evolved past the point of sapience. However, they exist in symbiosis with an intelligent invertebrate species termed the slugs, which inhabit the folds of nestbuilder exoskeletons and control their hosts through neural linkages.