The Nesk were a alien race of insects in Animorphs during the Cretaceous Period.
The Nesk were a hivemind race of sapient insects. They could come together to form any size creature they'd like when times called for it in order to operate tools. According to K.A. Applegate the Nesk are the ancestors of all Earth ants species.
The Nesk were known, during their era, as a race of scavengers that stole various technologies throughout the galaxy over the years. They settled on Earth around 65,000,000 B.C. and constantly warred with the Mercora, a peaceful race who had also settled on Earth.
After the Mercora aided the time displaced Animorphs in stealing a nuclear fission device, they evacuated Earth and directed an asteroid toward the planet to destroy both Mercora in an act of spite.
Culturally nothing is known about them but from several interactions the Nesk appear to be a scavenger race, dedicated to acquiring new technologies for themselves and highly very territorial beings.
- Megamorphs #2 In the Time of Dinosaurs.