The Wraith, as a result of this blending of genetic material, are humanoids who still require humans as a food source. An insect-arachnid type of 'bug' called the Iratus Bug fed on humans and the DNA from both species began to blend.
The evolution of the Wraith was the result of the Ancients' having introduced humanity to the galaxy, so, basically, the Wraith were accidentally created by the Ancients. During these millions of years, however, another new life form was also evolving: the Wraith.
The Ancients stayed in the galaxy hoping to exchange friendship and knowledge with these new societies. The story goes on to reveal that the human worlds prospered thereafter. A holographic recording made by an Atlantian Ancient from 10,000 years ago said that the Ancients had settled in Pegasus 'in the hope of spreading new life in a galaxy where there appeared to be none.' ( Stargate Atlantis: 1.01 'Rising Part 1') This event happened five to ten million years ago. When the Ancients arrived in the Pegasus Galaxy, they had just left the Milky Way after creating a second generation of humanity after a plague swept through and devastated their advanced human population.
