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Icaricia icarioides fenderi, Fender's Blue Butterfly

Photo of a Fender's Blue Butterfly

The Fender's blue butterfly, Icaricia icarioides fenderi, belongs to the group of Gossamer-winged butterflies within the family Lyaenidae. It is one of a dozen subspecies of Boisduval’s blue (Icaricia icarioides), but subspecies fenderi is considered a distinct taxon found only in the upland prairies of the Willamette Valley in western Oregon. Fender’s blue butterfly is quite small, having a wingspan of 2.5 centimeters; males manifest bright blue wings with a black border and basal area and females an inconspicuous, rusty-brown. The undersides of the wings of both sexes are tan with black spots, outlined by a white border. Caterpillars are small, solid green and appear humped in profile. In its larvae stage, it feeds primarily on Lupinus sulphureus spp. kincaidii, a lupine also endemic to the Willamette Valley and listed as threatened under the federal Endangered Species Act. As adults, their primary nectar sources are Allium amplectens and Sidalcea virgata.

The life history of the Fender’s Blue is not well documented; yet researchers believe it is similar to other subspecies of Icaricia icarioides. In May, eggs are oviposited on leaves of Kincaid's Lupine, and, once the larvae hatch, they feed on the plant until it senesces. Reaching their second instar in early summer, the caterpillars move to the base of the lupine and enter diapause (a state of developmental arrest), for the duration of winter. They activate again in March of the following year, feeding on lupine while growing in size through three to four instars before they enter their pupal stage. They emerge as adults in May, taking a total of one year to complete their lifecycle.

First documented in 1929, Fender’s blue butterfly was last observed in 1937 before rediscovered in 1989 by Hammond, et al., only to be listed as endangered in 2000. Surveys have concluded that Fender’s blue is distributed across 32 sites in 4 counties in the upland prairies of the Willamette Valley, a 209 km long and 32-64 km wide area in western Oregon. These habitats are fire dependent, and were historically burned by the Kalapuya people.  In the 1850s, when colonists forced the Kalapuya from their native lands, controlled burning stopped and natural succession followed, eliminating grassland habitats conducive to Fender’s blue. Degradation continues: currently, less than 400 hectares of upland prairie remain in the Willamette Valley, which is less than one percent of the original upland prairie. Habitat fragmentation from urban development, agricultural practices, silvicultural activities, and roadside maintenance has contributed to the decline of Kincaid’s lupine and available habitat. Land development and degradation of the Willamette Valley has been so severe within the past decade that only small segregated patches of habitat suitable for Fender’s blue exist. The Fender’s blue is also threatened by ‘natural’ factors, like invasion of nonnative species and natural succession. To exacerbate their plight, the Fender’s blue butterfly is not currently protected under the Oregon Endangered Species Act, making it more difficult to extend conservation ranges.

Possibility of extinction remains high due to their small population size, expansive habitat degradation, and succession. Studies by Cheryl Shultz and Paul Hammond show through their experiments on three different sites in the Willamette Valley that, if current conditions persist, only one site, Butterfly Meadows, would have a 90% probability of persisting over 100 years. At the same time however, conditions can be improved if efforts are made to sustain areas of contiguous land with Kincaid’s lupine. According to Mark Wilson of the U.S. Fish and Wildlife Service in Oregon, four measures are necessary to conserve the upland prairies of the Willamette Valley. First, contiguous sites must be preserved from natural and human-induced habitat degradation; second, the areas must be consciously managed, using methods like prescribed burning or mowing to inhibit natural succession; third, endemic grassland plants, like Kincaid’s lupine, need to be restored; fourth, more studies need to be conducted to expand scientific knowledge of the area. Some measures have taken place: Lupinus sulphureus spp. kincaidii seedlings are continually introduced in an effort to restore native prairie; tall oat grass and other nonnative invasive species are controlled; also, nature conservancies are working to preserve habitats through prescribed burning. At the same time, however, more efforts need to be undertaken to re-establish the species.


Robsinson, Andrew. 2002. Endangered status for Erigeron ducumbens var. decumbens and Fender's Blue Butterfly Icaricia icarioides fenderi anand threatend status for Lupinus sulphureus sp. kincaidii. Oregon Stat Fish and Wildlife Office: Salem Oregon: 65 (16) 3875-3889

Schultz, Cheryl and Crone, Elizabeth. 1998. Burning prairie to restore butterfly habitat: a modeling approach to managment tradeoffs for the Fender's blue. Resoration Ecology. Blackwell Publishing: Oxford. 6 (3) 244-248

Written by: Caitlin Kauffman, 2004

Updated 2008.

Image credit: Cheryl B. Schultz