Tweets,
We received this from UC Davis a while ago. I'm not sure it can still
be accessed on the web so I'm copying it for you. For many years I
worked at the California Raptor Center on the Davis campus. It was
adjacent to a levee along Cache Creek and you could see for long
distances. There were usually 3 to 4 days in March/April when the
number of migrating Ladies was truly amazing--a few times they were so
numerous I could sort of see a "layer" of butterflies.
I hadn't realized that our PNW Ladies are a 2nd generation.
Alice Swan
Orcas

> Date: March 28, 2005 4:05:40 PM PST
> To: ucdavis-news at ucdavis.edu, getnews at ucdavis.edu

> University of California, Davis
> March 28, 2005
>
> PAINTED LADY BUTTERFLIES ON THE WING
>
> Millions of painted lady butterflies invaded central California
> airspace Monday as a massive migration from the desert began to hit
> its stride. The insects are on their way from their winter grounds on
> the Mexican border to the Central Valley and foothills, where they
> will breed.
>
> The butterflies were moving by 7 a.m. and by mid-morning in Davis
> were passing at a rate of about one every 10 seconds, said Arthur
> Shapiro, professor of evolution and ecology at UC Davis and an
> authority on butterflies.
>
> The insects fly from six to about 12 feet above the ground on a
> southeast to northwest bearing and rise over obstacles, such as
> buildings, rather than going around them.
>
> The painted lady winters in the desert along the U.S.-Mexico border
> and breeds on desert annual plants in late winter. The adults emerge
> in February or March and immediately take off to the northwest,
> migrating through the Inyo-Kern area into the Central Valley and
> foothills where they then breed. The trip takes roughly three days in
> good weather, because the butterflies hatch with a large supply of
> yellow fat, which they use as fuel, Shapiro said.
>
> "This fat is what makes the yellow splotch on your windshield when
> you hit one," he said.
>
> When the fat supply is depleted, generally after reaching the Central
> Valley, they begin visiting flowers to feed and also begin laying
> eggs. The caterpillars feed on weeds such as thistles, mallows and
> fiddleneck. They are normally of no economic importance, although
> there are records of them wiping out crops of borage and comfrey
> (both in the same family as fiddleneck) at herb farms.
>
> The annual migration can occur as early as late-January and as late
> as mid-April. This year's migration is probably more conspicuous than
> usual because heavy winter rains in Death Valley and elsewhere
> produced a bumper crop of desert plants, Shapiro said.
>
> The butterflies resulting from breeding in our area will hatch in May
> and will also migrate immediately, flying north to breed in the
> Pacific Northwest.
>
> Shapiro said that the migration is apparently a way of tracking the
> seasonal progress of host-plant availability. Elsewhere in the world,
> painted lady butterflies winter in North Africa and migrate to Europe
> for the summer, sometimes reaching as far north as Scandinavia.
>
> The butterflies will begin to migrate south again in August,
> continuing through November, Shapiro said.
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