The infestation bug is an insect on the planetSvoriin that presumably killed the entire population and took over the planet.
The infestation bugs origin homeworld is Skaald. A sting from the infestation insect can change a person's DNA so the inside of the body can grow many new infestation bugs. The huge insect species of BP6-3Q1 has a venom that will transform the DNA of the victim, causing a metamorphosis into numerous new insects through equal matter conversion.
Each human would become approximately ten new insects, causing swarms in the millions within six to eight weeks.(SG1: "Bane")