These viruses suppress the larva's immune system and allow the parasitoid to grow inside the host undetected. Through the evolutionary history of being used by the wasps, these viruses apparently have become so modified, they appear unlike any other known viruses today. Because of this highly modified system of host immunosuppression, a high level of parasitoid-host specificity is not surprising. In other words, the viruses need to be a bit different for every host species.