An entry in Dieter E. Zimmer's Guide to Nabokov's Butterflies and Moths (2012) reads as follows:
*Eurema lisa Boisduval & LeConte, 1829 [Pieridae, Coliadinae]: one of the small sulphurs of the genus Eurema Hübner, 1819 whose type-species is Eurema daira Godart, 1819, the Barred Yellow. They all are of small to medium size (wingspan 28–38 mm), with yellow, orange or white as the ground color and maroon or black outer margins.
In Pale Fire, there is "that vortex of yellow and maroon butterflies that so pleased Chateaubriand on his arrival in America". They probably were Eurema butterflies. One can even say which species. William H. Howe in The Butterflies of North America (1975, p. 371): "Despite their small size and delicate appearance, some of these butterflies are capable of long sustained flight and periodically engage in tremendous migrations containing millions of individuals. Huge squadrons of Eurema lisa have been reported in flight both over land and far at sea. These migrations predate history in the New World and it was probably a swarm of either Eurema lisa or Phoebis eubule that Columbus and his crew saw about the Santa Maria near the south coast of Cuba." As »Phoebis sennae eubule has no maroon, the vortex of butterflies Chateaubriand saw on his arrival in America will probably have been Eurema lisa. Nabokov saw it in Wellesley, Massachusetts, in the warm fall of 1946.
*PaleF 247; Lep11 42
To begin with the end, I find no explicit source for the mention of what Nabokov doubtlessly witnessed in Wellesley in 1946 though, evoking that place and time, Brian Boyd refers to an interview he had with Charles Remington, head of entomology at Yale, to suggest Nabokov saw such swarms (in a 1953 article, having collected in Wyoming, he would make the link with the Old World and with "migratory flights from beyond the Black Sea hit[ting] the south of the Crimea in April, and females, bleached and tattered, reach[ing] the Leningrad region early in June").
As for Columbus, second-hand accounts do say how, off the coast of Cuba, "the whole air would be filled with clouds of butterflies, until the evening shower would dispel them."
My query is about Chateaubriand. Kinbote mentions that page—is he to be trusted? I could not find any mention of "that vortex of yellow and maroon butterflies that so pleased Chateaubriand on his arrival in America." Not in the Voyage en Amérique, not in Mémoires d'outre-tombe either, not in Atala, The Natchez, or the letters for that matter.Two eminent colleagues, specialists of Chateaubriand, could not help me.
Any suggestion?