Fender’s blue or silvery blue butterfly? And other entomological adventures

By Jessica Celis

April 2019

IAE’s restoration ecologists tend to focus on plant communities. But this year, three of HR’s five restoration ecologists will shift their search image from plants to butterflies as they participate in the annual range-wide survey for Fender’s blue butterfly, which is funded each year by the US Fish and Wildlife Service, with assistance from Oregon State Parks. Fender’s blue is an endangered Willamette Valley (Oregon)-endemic species that uses the threatened plant species Kincaid’s lupine as its primary host plant. All of IAE’s restoration ecologists manage sites that are home to threatened and endangered species; four of those five ecologists work at sites that contain Kincaid’s lupine. Successful prairie habitat restoration and preservation of Fender’s blue sites across the Willamette Valley is putting this species on the path to recovery, making an annual census of the butterfly critical to track its progress.

In April, IAE’s Peter Moore, Andrew Esterson, and Jessica Celis attended a Fender’s blue butterfly monitoring training hosted by Rhiannon Cochrane (US Army Corps of Engineers Botanist) and Duncan Thomas, Ecologist, in preparation for the emergence of the Fender’s blue adults. Surveying for these tiny blue butterflies can be tricky, since they have several look-alike species, namely the silvery blue. Both species are small, blue, and overlap in their adult phase. Through this training, we learned the key physical, life history, and behavioral characteristics that distinguish these two butterflies. Also covered in our training was the protocol for conducting distance sampling and modified peak counts, the two primary monitoring techniques used for estimating butterfly population size, to ensure that this year’s monitoring efforts are conducted consistently across sites.

If you happen to get a bird’s eye view of these two look-alikes, you will want to look for a few key distinguishing physical characteristics. Figure 1 shows specimens of both species, and arrows point out two of the characteristics that distinguish Fender’s from silvery blue butterflies. The white arrows point out the submarginal band of the butterflies; Fender’s blue has two, the silvery has only one. The gray arrows point to the end bar spot, which is generally wider in Fender’s blue than it is in silveries. Take note that while Fender’s blue butterflies are endangered, silvery blues are quite common, so chances are high that you are seeing a silvery blue or other similar blue butterfly.

Figure 1. Silvery blue butterfly (top) and Fender’s blue (bottom). Arrows point out two of the characteristics that distinguish Fender’s from silvery blue butterflies. The white arrows point out the submarginal band of the butterflies; Fender’s has two, the silvery has only one. The gray arrows point to the end bar spot, which is generally wider in Fender’s than it is in silvery. A final characteristic is the arrangement of the spots on the lower wing – in silvery blues, it is in an omega shape, while in Fender’s blue, it is a more regular curve.

We restoration ecologists are enthused to utilize our newly acquired knowledge and to be a part of the census of this unique Willamette Valley species, and excited to have an even more in-depth view of how IAE’s habitat restoration benefits endangered species! For more information on the Fender’s blue butterfly and the annual monitoring that is coordinated by IAE see Carolyn Menke’s “Flight of the Fender’s Blue” blog, and search our website.

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