Kandrona rays

Kandrona ray generator in the TV series

"The Kandrona is a miniature version of the Yeerks' home sun. It emits Kandrona rays, which concentrate in the Yeerk pools. It is what nourishes the Yeerks. That is why the Yeerks must swim in their natural state in the Yeerk pool every three days — they need Kandrona rays."

―Ax

Kandrona rays are the Yeerks' required source of sustenance, naturally emitted by the sun of the Yeerk homeworld. Portable Kandrona generators were created to emit artificial rays, which allowed the Yeerks to survive off of their planet.

Overview

Kandrona rays are particles naturally emitted by the sun of the Yeerk homeworld. The rays are projected onto the Yeerk pools on the planet and served as the only sustenance that the Yeerks biologically required. In the 1960s, the Andalite Prince Seerow arrived on the Yeerk homeworld, where he studied and interacted with the Yeerks. In order to help them survive off-planet, Seerow invented portable Kandrona generators that would generate Kandrona rays. During their mutiny and exodus in 1966, the Yeerks took the portable Kandrona generators with them, allowing them to have constant access to Kandrona rays.

When the Yeerks infiltrated other planets, they constructed Yeerk pools and installed a portable Kandrona that would always be emitting Kandrona rays into the pool. However, the Kandrona rays were seen by many to be a weakness to the Yeerks since every three days, a Yeerk would have to exit their host and consume Kandrona rays in order to survive; this liability prevented them from remaining in a host for over three days or to be in an environment without access to Kandrona rays.