Dr. James Marcus began his research into the viability of t-Virus B.O.W.s soon after its 1978 creation. The Plague Crawler was one such species created though using the virus for purposes of deliberate genetic modification. In regards to this particular species, its origins lie in the merging of DNA from multiple insect species, using the t-Virus as a sort of bonding agent.
While the Plague Crawler species proved that viable bio-weapons could be created through the virus, they were regarded by Marcus as a failure due to their lack of intelligence and control, which made them impractical for military use. Marcus made preparations for the entire species to be destroyed as waste at the Umbrella Executive Training Center, though some Plague Crawlers managed to escape destruction and survived in the complex until 1998.
Research data on the creatures appears to have survived the destruction of the facility, as samples were purchased by Javier Hidalgo at the turn of the 21st century as low-cost bioweapons. These B.O.W.s were last seen during Operation: Javier in the 2002 Amazon rainforest by Leon S. Kennedy; Jack Krauser and Manuela Hidalgo when Javier had them captive in his torture/prison chamber where countless victims met their demise by these creatures.