Creature approximately 19 centimeters (7.5 inches) in length, naturally emitting a form of radiation never before encountered by Stargate Command. It lodges itself in the stomach lining of a larger creature and begins to rewrite the D.N.A. of the host. Eventually the mutant result is a powerful carnivore.
The parasites are known to the Sodan, who may have first encountered them when they developed their cloaking technology. The Sodan, who are Jaffa, were able to tolerate a field of radiation which they installed into their technology to specifically prevent these parasites from appearing in this universe.
Once lodged into a host body the larger animal remains susceptible to this Sodan radiation, and is a potent Achilles heel to corral and take down the larger animal.
Uninvited - Stargate Command personnel are dismayed to discover that their enhancements to Sodan cloaking devices, meant to prevent a regular dose of radiation exposure to their personnel, have admitted dangerous parasites into our universe.