From TARDIS Index File, the free Doctor Who reference.

Annarenes are thin, orange humanoids. Though nearly the height of a Human, they are as thin as sticks and roughly as durable. In order to pass as Humans, they need such disguises as fleshsuits. They have an orange exoskeleton, small bumps around their head and body and strangely Human eyes. Though they aren't harmed by it, Annarenes greatly dislike the cold and wetness.

Although the Annarene Protectorate were originally a dangerous force in the Mutter's Spiral, they started forming more peaceful alliances. The Tulkan Empire took this for a sign of weakness and invaded. They were stopped and their leaders were all mind-wiped and left on Earth. Despite this, many Annarenes felt that the Protectorate had become weak and ineffective and tried to find ways to gain a strategic advantage. (PDA: Relative Dementias)