Fender’s Blue Butterfly – State Wildlife Action Plan

Adult Fender’s blue butterflies are small, having a wingspan of approximately 25 mm. The upper wings of males are brilliant blue in color with black borders and basal areas, whereas the upper wings of females are completely brown. The undersides of the wings of both sexes are cream-tan with small, black spots surrounded by a fine white border or halo. In the larval state, this species emerges as a reddish-pink color before changing to solid green and appears humped in profile. The eggs are small, 2 mm in diameter, puck shaped, and white when unhatched.

Overview

Species Common Name Fender’s Blue Butterfly
Species Scientific Name Icaricia icarioides fenderi
Federal Listing Status Threatened

Ecoregions

Willamette Valley

The Willamette Valley ecoregion is bounded on the west by the Coast Range and on the east by the Cascade Range. This long mostly level alluvial plain has some scattered areas of low basalt, and contrasts with productive farmland and large urban areas. It has the fastest-growing human population in the state resulting in challenges due to land-use changes.

Special needs

Fender’s blue butterflies are restricted to native upland prairie and oak savannah habitats in the Willamette Valley. They depend on specific species of lupine throughout their entire life cycle. Kincaid’s lupine is the most frequent larval host plant, but will also utilize longspur lupine and sickle-keeled lupine. Nectar from wildflowers is essential for adults and is their sole food source.

Limiting factors

Principal threats to Fender’s blue butterfly are habitat loss and degradation. The rarity of host lupine patches and fragmentation of habitat limit reproduction, dispersal, and colonization of new habitat. Invasive vegetation, especially tall grasses, can inhibit the growth of the lupine host plants and native nectar sources. Insecticides and herbicides are threats to all life stages. The limited dispersal ability of this species may make it vulnerable to climate change, especially with predicted losses of nectar and host plants.

Data gaps

Research metapopulation dynamics. Develop reliable and effective methods for managing and controlling herbaceous invasive species. Investigate the effects of increased temperatures under different climate change scenarios on the development rate of this species and lupine growth cycles.

Conservation actions

Maintain and restore native prairie habitat and populations of host lupine. Use prescribed fire and mowing to remove invasive vegetation and reduce woody succession. Use caution when implementing gypsy moth and mosquito control. Work with landowners to protect critical habitat. Monitor metapopulations and habitat. Maintain a 0.5 – 1.0 km distance between lupine patches within a metapopulation to promote connectivity.

Key reference or plan

Reclassifying Fender’s Blue Butterfly from Endangered to Threatened with a Section 4(d) Rule. 2023. Read here

Species Status Assessment. 2020. Read here

Recovery Plan For The Prairie Species Of Western Oregon And Southwestern Washington. 2010. Read here