Auxiliary Tribe

An Auxiliary Tribe is an additional tribe introduced to the game, often during a Tribe Swap, in the premerge portion of a season.

Survivor: Resurrection
On Day 10, was introduced to the game during the first tribe swap, spreading the remaining twenty castaways over four tribes. Bizet lasted until the merge.

Survivor: Hallasan
On Day 4, was introduced to the game at the first tribe swap, splitting the fifteen castaways into three tribes of five each. Donnaeko lasted until the merge.

Survivor: Tibet
On Day 11, was introduced to the game as a third tribe at the swap, spreading the fifteen remaining players across three tribes of five. Lhotse lasted until the merge.

Survivor: Egypt
On Day 10, was revealed as a third tribe at the swap, splitting the fifteen remaining castaways into three tribes of five each. Horus was dissolved on Day 17 prior to the mutiny.

Trivia

 * Two of the four auxiliary tribes so far have been purple.
 * Three of the four swaps involving auxiliary tribes have split fifteen castaways across three tribes of five each.
 * Bizet is the only auxiliary tribe revealed during a swap to be the fourth premerge tribe of the season, instead of the third.