Documenting Fender’s blue butterfly

It is butterfly season here in Eugene, Oregon and the Fender’s blue butterfly (Icaricia icarioides fenderi) has already reached its seasonal peak and is on the down slope much earlier than expected.  For most of my position with the West Eugene Wetlands I primarily monitor endangered/rare wetland plants.  However, along with one of our monitored plant species, Kincaid’s lupine (Lupinus oreganus), is the Fender’s blue butterfly (FBB) that uses this endangered lupine as its larval host, laying its eggs on the underside of the plant’s leaves.

Myself with Kincaid's lupine (Lupinus oreganus)

Myself with Kincaid’s lupine.

One of the more populous BLM sites in Eugene for both lupine and FBB is Fir Butte, where I get to spend glorious afternoon after glorious afternoon catching butterflies.  This is something I did in my childhood and never imagined I would be getting paid to do later on in my adulthood.  In addition to FBB there is a look-a-like, the silvery blue butterfly (Glaucopsyche lygdamus) or SBB that also uses Kincaid’s lupine as a larval host, but instead lays its eggs along the stalk of the flowering raceme.  There are two minute physical differences between these species that we use as identification features when netting the butterflies.  First is the markings or “dots” along the border of the underside of the wings.  On SBB there is one row of dots and on FBB there are two rows of dots that can sometimes be very visible and other times, usually with an older butterfly, nearly impossible to distinguish.  So that is why we use the second identification feature for “back up”.  The cell-end bar located on the fore wing of the butterflies in from the row of markings is much narrower on the SBB than the FBB.  In addition, the row of dots on SBB are much more circular than on FBB which tend to be more irregular-shaped spots.


A male Fender’s blue butterfly  with damaged wing.  Notice the faint second row of irregular-shaped markings along the wing border and the large cell-end bar.

Mating pair of Fender's blue butterfly.

Mating pair of Fender’s blue butterflies. (Awesome photo skills of Christine Calhoun).

pair of silvery blue butterflies mating.

Mating pair of silvery blue butterflies.  Notice the one row of circular markings along the wing border.

Our first mode of action in sampling FBB is to take a ratio of male FBB to male SBB.  My mentor, Christine, and I spread out among the lupine at Fir Butte with our nets and each sample around 10 to 15 butterflies.  We then determine whether the butterfly is Fender’s species or silvery as described above.  Second, we determine its sex by noting the color on the top of the wings.  Males in both species are a bright blue and female FBB are copper-colored whereas female SBB are a darker brown, both females have some blue on the body of the butterfly. We record all sexes of both species but use only the ratio of males to males for our next mode of action, distance sampling, as it is much easier to see a bright blue male flying or sitting than it is to spot a brown female among the foliage.  Distance sampling occurs along six transects stretching the length of Fir Butte.  One person walks the transect with a distance pole held perpendicular to the transect calling out to the second person, the recorder, the distance (in half-meter increments) from the center of the transect the male butterfly was seen along with information on whether it was flying or sitting, the cluster size, and sex ratio if females were in the cluster.  An ideal day for sampling FBB is above 60 degrees, a light breeze, and sunny.  It’s the most optimal conditions for the butterflies and I’d say the most optimal for me, too.  Who doesn’t like 60 degree sunny days?

Male Fender's blue butterfly.

Male Fender’s blue butterfly.

Female Fender's blue butterfly on its larval host, Kincaid's lupine.

Female Fender’s blue butterfly on its larval host, Kincaid’s lupine.

Other efforts towards the success of the Fender’s blue butterfly are being put forth by some members of the West Eugene Wetlands Partnership such as the Institute of Applied Ecology who are making “nectar islands” at Fir Butte.  Some native nectar species of FBB include Checkermallow (Sidalcea malviflore), Oregon geranium (Geranium oreganum), Camus (Camassia quamash and C. leichtlinii), Oregon sunshine (Eriophylluym lanatum), and the Oregon iris (Iris tenax).

Thanks for listening and ta-ta for now.

Danica Maloney

West Eugene Wetlands


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