Blerks originated from an unnamed lifeless planet that Zim crashed on. The fluid from his Voot Cruiser mixed with the materials on the planet, causing a sort of primordial pool to appear and fill the planet with life. The life forms on this planet are in a state of extreme hyper-evolution, reacting to even the smallest touch.
The Blerks were ultimately destroyed by Zim, as they had taken his voot cruiser and Zim needed it back. Zim created the Battleslug 7000, attached many weapons onto it, and eliminated the Blerks. This became known as "The Blerk Wars of 15,010".
Presumably this rendered the Blerks extinct, though even if any survived, they would have then been destroyed when Zim blew up the planet upon leaving.
The Blerks originally started out as harmless lady bug-like creatures. But after GIR touched one of them, they grew in size and became angry and hostile. They attacked, and Zim destroyed them with his PAK lasers. Since they are in a state of hyper-evolution, they evolved an immunity to said lasers in their subsequent attack.
The native single celled residents of the unnamed planet described the Blerks as powerful creatures, having strong shells and sharp teeth.
- They are only called Blerks by the native residents of the planet. Zim and GIR simply call them "lady bugs", obviously due to their appearence looking like that of Earth's lady bugs.