Fender's blue butterfly was listed as endangered in 2000. Critical habitat was designated in 2006. This butterfly does not have a recovery plan.

Historical Status and Current Trends

This subspecies of the Boisduval's blue butterfly (Icaricia icarioides) was believed to be extinct from 1937 until it was rediscovered in 1989. The distribution of this butterfly is restricted to the Willamette Valley, Oregon, where it currently occupies 32 sites in Yamhill, Polk, Benton, and Lane Counties. One population is found in wet, Deschampsia-type prairie, while all other remaining populations are found on drier, upland prairies characterized by Festuca (forage grasses) species. 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 and at Willow Creek Main Preserve managed by The Nature Conservancy.

Habitat

Fender's blue butterfly occurs in native prairie habitats. Most Willamette Valley prairies are early seral (one stage in a sequential progression) habitats, requiring natural or human-induced disturbance for their maintenance. The vast majority of these prairies would eventually be forested if left undisturbed. Fender's blue butterfly is typically found in native upland prairies, dominated by red fescue (Festuca rubra) and/or Idaho fescue (F. idahoensis), where its primary larval food plant, Kincaid's lupine (Lupinus sulphureus kincaidii) or its secondary larval food plants sickle-keeled lupine (L. albicaulis) and spur lupine (L. arbustus) also occur. Its primary larval food plant, Kincaid's lupine (listed as Threatened), occurs on a few, small prairie remnants in the Willamette Valley. Native plants, including Tolmie's mariposa (Calochortus tolmiei), Hooker's catchfly (Silene hookeri), broadpetal strawberry (Fragaria virginiana), rose checker-mallow (Sidalcea virgata), and common lomatium (Lomatium spp.) also occur on native upland prairies and serve as herbaceous indicators of prairie condition. These dry, fescue prairies make up the majority of habitat for Fender's blue butterfly. Although Fender's blue butterfly is occasionally found on steep, south-facing slopes and barren rocky cliffs, it does not appear to thrive in the xeric oatgrass communities often found there.

Description

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 Kincaid's lupine leaflet. The egg soon hatches and the larva feeds on lupine leaflets. The larva may pass through one molt before dropping to the ground in mid-June or July where it goes into 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 molts, it ecloses into a butterfly in May and begins the cycle again.

Reasons for Decline

Fender's blue butterfly is endangered because native prairie habitat has been converted to agriculture, subjected to fire suppression, invaded by non-native plants, or otherwise developed. Refugia from these forces of change are mostly limited to fence rows and intervening strips of land along agricultural fields and roadsides. Even these areas are disappearing now as private landowners come under increasing pressure to develop. By nature, prairies are a transient community, 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 Kincaid's 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.

Loss of native prairie has resulted in the isolation of butterfly populations which were once inter-connected. As the number of sites declines and the distance between them increases, opportunities for adult movement between populations are reduced. Populations isolated in this manner face a higher risk of extinction because they are more vulnerable to natural and human-made disturbances.

Conservation Measures

Natural processes which functioned to maintain open prairies have been altered and non-native plant species have invaded most sites. Historically, large-scale fires played a role in maintaining prairies in an open state. Fires kept shrubs, trees, and most non-native species from invading. Today, prairie remnants are no longer maintained by fire due to suppression efforts. Human intervention, including management, restoration and protection, is needed to prevent further loss. Currently, controlled burning, careful mowing, and hand clearing are used to manage prairie ecosystems.

References and Links

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 for Lupinus sulphureus ssp. kincaidii (Kincaid's Lupine). FR (65): 3875-3890.