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Fender's blue butterfly

Photo of Fender's Blue Butterfly (Credit: sally gentry)

Scientific name: lcaricia icarioides fenderi

Status: Endangered, Proposed for Downlisting

Critical Habitat: Designated

Listing: Fender's blue butterfly was listed as endangered in 2000. Critical habitat was designated in 2006. A recovery plan was published in 2010. 

Potential Range Map

  • Historical Status and Current Trends

    The Fender’s blue butterfly is a subspecies of Boisduval's blue butterfly (Icaricia icarioides) found only in the upland prairies of the Willamette Valley in western Oregon. It was believed to be extinct from 1937 until it was rediscovered in 1989. As of 2018, there are a total of 15 known Fender’s blue butterfly metapopulations and 6 independent groups in Benton, Lane, Linn, Polk, Washington, and Yamhill Counties. Sites occupied by Fender's blue butterfly are located almost exclusively on the western side of the valley, within 33 kilometers (21 miles) of the Willamette River. The largest populations occur at Baskett Slough National Wildlife Refuge, the West Eugene wetlands area, and Willow Creek Main Preserve managed by The Nature Conservancy.


    Fender's blue butterfly occurs in early seral (one stage in a sequential progression) prairie habitats, requiring natural or human-induced disturbance for their maintenance. If left undisturbed, the vast majority of these prairies would eventually become forested. The association of Fender’s blue butterfly with upland prairie is a direct result of its dependence on three specific species of lupine throughout its entire life cycle: Kincaid's lupine (Lupinus sulphureus kincaidii), sickle-keeled lupine (L. albicaulis), and spurred lupine (L. arbustus). Lupine plays an integral function in Fender’s blue butterfly reproduction because the plants provide the sole food source for the developing larvae. Kincaid's lupine (listed as Threatened) is the most frequently used larval host plant. Adult Fender’s blue butterflies use a variety of plants as nectar sources; these include: tapertip onion (Allium acuminatum), narrowleaf onion (Allium amplectens), Tolmie's mariposa lilly (Calochortus tolmiei), small camas (Camassia quamash), clearwater cryptantha (Cryptantha intermedia), wooly sunflower (Eriophyllum lanatum), Oregon geranium (Geranium oreganum), toughleaf iris (Iris tenax),pale flax (Linum angustifolium), blue flax (Linum perenne), Meadow checkermallow (Sidalcea campestris), rose checker-mallow (Sidalcea virgata), bird vetch (Vicia cracca), common vetch (V. sativa), and tiny vetch (V. hirsute). Native plants that occur on native upland prairies serve as herbaceous indicators of prairie condition.


    Fender's blue butterfly is a relatively small butterfly with a wingspan of approximately 2.5 centimeters (1 inch). The upper wings of the males are brilliant blue with a blackish wing margin and a white fringe of scales. The upper wings of the females are brown with a white fringe of scales. The undersides of the wings of both sexes are creamish-tan with black spots surrounded by a fine, white border or halo.

    Life History

    The life cycle of a Fender's blue butterfly begins in late spring or early summer when an adult female deposits an egg on the underside of a lupine leaflet. The egg soon hatches and the larva feeds on lupine leaflets. The larva passes through multiple instars before dropping to the ground in mid-June or July, where it goes into a state similar to hibernation for the fall and winter. In the following March or April, the larva begins to feed on fresh lupine leaflets again. After three to four additional instars, the larva pupates, emerging as a butterfly in May and beginning the cycle again.

    Reasons for Decline

    Fender's blue butterfly was listed as endangered because of habitat loss from a wide variety of causes (e.g., urbanization, agriculture, silvicultural practices, and roadside maintenance); encroachment of shrubs and trees into prairie habitats due to fire suppression; fragmentation; invasion by nonnative plants; and elimination of natural disturbance regimes. By nature, prairies are transient communities, requiring disturbance to prevent a transition to forest. With extensive changes in the fire regime, disturbances that maintained native prairies have been substantially altered, allowing tree and shrub species to invade and shade out low-growing lupine, the species upon which this butterfly depends. In addition, non-native species such as Himalayan blackberry (Rubus discolor) aggressively overtake open spaces and crowd out native species.

    Conservation Measures

    Upland prairie sites that do, or that could, support Fender’s blue butterflies generally require routine treatment to remove woody vegetation and invasive plants in order to maintain and enhance the native plant community and open prairie conditions. Many agencies and private landowners are working collaboratively on habitat protection and habitat restoration efforts such as controlled burning, careful mowing, and hand clearing of vegetation to benefit both the Fender’s blue butterfly and its prairie habitat. Ultimately, the conservation and recovery of Fender’s blue butterfly, Kincaid’s lupine, and the suite of native species associated with them will rely in large part on the voluntary actions of many willing non-Federal landowners to conserve, enhance, restore, reconnect and actively manage native prairie habitats that support these species.

    References and Links

    U.S. Fish and Wildlife Service. 2006. Designation of Critical Habitat for the Fender's blue butterfly (Icaricia icarioides fenderi), Lupinus sulphureus ssp. kincaidii (Kincaid's lupine), and Erigeron decumbens var.decumbens (Willamette daisy): Final rule. FR 63861 63977.

    U.S. Fish and Wildlife Service. 2000. Endangered Status for Erigeron decumbens var. decumbens(Willamette Daisy) and Fender's Blue Butterfly (Icaricia icarioides fenderi) and Threatened Status forLupinus sulphureus ssp. kincaidii (Kincaid's Lupine). FR (65): 3875-3890.


    Last updated: December 2019

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