1984 – The U.S. Fish and Wildlife Service designated the Thorne's hairstreak butterfly as a Category 2 candidate for listing under the Endangered Species Act.
June 4, 1991 – The San Diego Biodiversity Project petitioned the Service to list the Thorne's hairstreak and Hermes copper butterflies as endangered.
July 19, 1993 – The Service rejected the 1991 petition to list the Thorne's hairstreak on a technicality, alleging that it lacked necessary information (while simultaneously admitting to already possessing this same information). While the Service promised to conduct a status review of the species, there is no evidence that it did so.
July 19, 1995 – The Thorne's hairstreak's Category 2 candidate status was removed when the Service unilaterally abolished the Category 2 candidates list.
October 25, 2004 – The Center submitted a petition to list the Thorne's hairstreak and Hermes copper under the Endangered Species Act.
October 18, 2005 – The Center filed suit against the Service for failing to respond to conservation groups' two petitions to list the Thorne's hairstreak and Hermes copper butterflies.
August 8, 2006 – Despite the fact that the Thorne's hairstreak butterfly had been devastated by fire and other threats that still posed a significant danger to the butterfly, the Service announced in its 90-day finding that it would not list the species under the Endangered Species Act.
March 17, 2009 – The Center filed a second suit against the Service seeking federal protection for the Thorne's hairstreak and Hermes copper butterflies.
October 26, 2009 – Through a legal settlement with the Center, the Service agreed to reconsider our petitions to protect the Hermes copper and Thorne's hairstreak butterflies.
April 5, 2010 – The Service announced that the Thorne's hairstreak warrants consideration for federal protection as an endangered species and began soliciting public comments on the species' endangerment.
February 23, 2011 – The Service again denied protection to the Thorne's hairstreak.