Invasion of the California Tortoiseshells

How to follow up with the first Mulberry Wing Skipper photographed in Nebraska? Colin Croft was kind enough to share his experience from July 11.

With a relatively milder day forecast for Monday July 11th, I headed off north into Sioux
County from Scottsbluff/Gering to check up on my little quarter section of pasture about
15 miles southeast of Harrison. On the way, as I usually try to do, I swung into Agate
Fossil Beds National Historic Site (River Road exit east off Highway 29) to check for
butterflies, bees and anything else that might present itself. In my experience, that first ½ mile stretch east of Highway 29—including the adjacent roadsides of Highway29—can be very productive when any of the native species are in bloom. I was pleased to see that much of the milkweed (mainly A. speciosa) was well into bloom, as was plenty of wild licorice and a few other pollinator-attractive species. I quickly spotted a Monarch and a Regal Fritillary (both my first of this season…seems late!), and then an Anise Swallowtail that persisted long enough for me to get some decent photos. A Mourning Cloak zipped by too quick for me to grab a photo as I pushed into the brushy lower areas on the north side of River Road. This wasn’t marsh-suffering of the kind Neil and Jonathan recently endured for their Mulberry Wing Skipper, but the occasional nettle had me wishing I had brought a change of long pants!

I was working closer to a bumblebee to try to add to Bumble Bee Watch, when I saw a
butterfly light on a milkweed bloom to my left. Wings closed it looked like a comma, but
when partially open the coloration had me thinking Milbert’s Tortoiseshell (not
uncommon in this area). Well identification could come later, now was the time to get
some decent photographs, which the butterfly happily obliged! In fact, it flitted around
me for several minutes, reminding me of some of the commas and Hackberry Emperors
that always seem so “friendly” or at least curious compared to other species. I didn’t
have a lot of time to spend at Agate since I had a few other spots to visit and things to
do on the pasture, but I stuck around long enough to see a couple of Ruddy Coppers, a
Delaware Skipper and some wood nymphs. The butterfly action was a bit slow to the
north at my pasture, except for several Regal Fritillaries I flushed while walking about
checking for invasive thistles. As in previous years, all of the Regals I flushed came out
of thicker/taller (1-2’) patches of still-green grasses; any management practice that
intentionally leaves at least some of these taller grass patches ungrazed, uncut, etc.
would seem to benefit the Regals, at least in this neck of the woods. My pasture has
been intentionally ungrazed for several years, so several of these taller grass patches
are available on some of the swales on the property.

When I got home and had the chance to inspect my photos more closely, I discovered
that I had been treated to an unusual “traveler”—a California Tortoiseshell (Nymphalis

Nymphalis californica, Agate Fossil Beds area, Sioux Co., NE, July 11, 2022, photo by Colin Croft
Nymphalis californica, Agate Fossil Beds area, Sioux Co., NE, July 11, 2022, photo by Colin Croft

Maybe Neil can weigh in with some additional information on this species,
but from my brief research, this species is “prone to long-range flights, sometimes in
large numbers, and may wind up far from regular breeding ranges” (Kaufman, Field
Guide to Butterflies of North America). A BugGuide contributor noted that one had been
spotted in Vermont (see some observation records in the US here)! The only other
Nebraska sighting I could find was a historical sighting in Dodge County. Maybe this is an irruption year for this species such that some other Nebraskans can see one. Colin Croft

Editors Note: This does appear to be an “irruption year”! Steve Spomer and Matt Brust each captured a California Tortoiseshell at Gilbert-Baker SWMA on the same day (July 11). So following up a first ever pic of a Mulberry Wing Skipper in NE is a first ever pic of a California Tortoise Shell in NE. We’re on a roll! Apparently this year presents a unique opportunity to sight this unusual (for NE) species. So keep an eye out for this butterfly that only rarely strays into the state (your chances will likely improve farther west in the state). Neil

Anise Swallowtail, Agate Fossil Beds area, Sioux Co. NE, 7/11/2022, photo by Colin Croft

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