Fender's blue butterfly (Icaricia icarioides fenderi) is an endangered subspecies of Boisduval's blue (Icaricia icarioides) endemic to the Willamette Valley of northwestern Oregon, United States. The potential range of the butterfly extends from south and west of Portland, OR to south of Eugene, OR. The butterfly is host-specific on the Kincaid's lupine, which it relies on for reproduction and growth.
Fender's blue butterfly is endemic to the Willamette Valley in Oregon, where its habitat is fragmented into 13 sections. Observation of butterfly dispersion and flight patterns revealed that butterflies tend to prefer prairie patches with Kincaid's lupine. As fragmentation increases the distance between lupine patches, the butterflies face habitat loss due to the lack of ability to fly from one patch to another. The increasing presence of anthropogenic structures, agriculture, and urbanization threaten habitat fragmentation, as roads can prevent movement and introduce mortality risk from vehicles.
In January 2000, Fender's blue butterfly was added to the Endangered Species List by the U.S. Fish and Wildlife Service. The largest known populations now exist in the Baskett Slough National Wildlife Refuge. A 2014 study reintroduced this subspecies to William L. Finley National Wildlife Refuge.
Fender's blue butterfly is a protected species in The Nature Conservancy's Willow Creek Preserve in Eugene, which extends into the Willamette Valley. Controlled burning of prairie habitats is practiced in the preserve to maximize butterfly population growth.
