Phoebis sennae part 2 (longish)

Rob (Robert) Hilton robert at
Fri Sep 8 12:22:22 EDT 2000

The Mystery of the Cloudless Giant Sulphurs (Phoebis sennae)
Part 2

"Bursting out of Texas, Lyside [Kricogonia lyside] often invades the
Arkansas Valley and other watersheds of the western Great Plains." 

"Although fairly common far north in late summer, the Little Yellow [Eurema
lisa] cannot survive temperate or northern winters. The species refills the
Northeast and Midwest every year with fresh immigrants, which furnish 1 or
2 more broods before the autumn chill kills them. Vast numbers of Little
Yellows emigrate to the Caribbean and Atlantic. Columbus is supposed to
have witnessed from the decks of the Santa Maria one such mass movement,
probably consisting of this species _or the Cloudless Giant Sulphur_." (One
might reflect on the changes to the flora of eastern North America since

"This sulphur [Sleepy Orange--Eurema nicippe] cannot withstand cold winters
yet annually penetrates the northern latitudes--_a characteristic of many
North American butterflies_...Northern individuals are usually more
dispersed, and may turn up in surprising places--well up a Colorado canyon,
for example, or along a Great Lakes shoreline."

"Each year, if conditions are favorable in the South, cadres of Dwarf
Yellows [Nathalis iole] advance northward from Mexico and the southwestern
desert, reaching as far as interior Canada. Recently, a much less frequent
or obvious emigration to the Northwest _and the Northeast_ has been
detected, recorded many years and miles apart, but always along major river
courses such as the Snake and _the Shenandoah_. Whether individuals travel
great distances themselves, or leapfrog northward through successive broods
is not yet clear. Unable to withstand the frosts of winter, _the Dwarf
reenacts its invasion of the North each year_, only to perish with the
coming of autumn."

However, the account for Phoebis sennae conflicts with my personal experience:

"Summer movements bring this sulphur to states far north of its winter
range, and _autumn emigrations greatly reinforce its northern numbers_,
sometimes introducing millions to relatively small areas. This butterfly's
appearance in the Rockies or New York is a real event. Yet _all of these
northern emigrants die without returning south_; the function of the
emigration is not really known. The Tailed Giant Sulphur (P. neocypris)
somewhat resembles the Cloudless, but it is larger and bears stout,
turned-in tails on the hindwings. It emigrates _seaward_ in great numbers,
yet is rarely encountered north of Mexico."

We have here a genuine mystery. The recorded natural history of this
species seems to contain errors or at least needs updating. Perhaps
sometime in this century field observers will get involved enough to solve it.

--Bob Augustine raugustine at

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