Sunday, August 16, 2009

Eastern Tiger Swallowtail

This male Eastern Tiger Swallowtail, Papilio glaucus, seemed to enjoy the Butterfly Bush in my yard. One coloration of the female has an area of blue in tail area between yellow and black. See the text below for more on this species' dimorphism.

From Every-Day Butterflies:

"This is, indeed, one of the most interesting examples of dimorphism known, since it is limited not only sexually, but geographically. It is found only where the insect develops more than one brood a year: at first, farther north, where there are but two annual broods, in a feeble way; but farther south, and apparently only where a third brood becomes common, to such an extent that nearly or quite all the females share it, and the species becomes completely antigenic, i. e., all the males are of one color and all the females of another. Yet though it appears to require the occurrence of a third, or at least of a second, brood to develop this antigenic quality, the feature is not at all confined to the later broods, but occurs to an equal extent in the spring brood. From its geographical limitation to regions where the species is more than single-brooded, we should naturally presume that this variation first arose in a summer brood ; that it should have extended so as to include the spring brood to an equal extent, and yet never to include the male, nor to have spread to regions where the species has but one brood, is certainly surprising. Weismann presumes this to be a case arising from sexual selection, but there seems to be not the slightest ground for such a belief. May it not be compared rather to those cases of mimicry, or of protective resemblance, often confined to the female sex, as the most needy object ? The black female must be a less conspicuous object than its gayly banded sister; and its restriction to the south is in keeping with the greater prevalence there of insectivorous creatures."

Scudder, Samuel Hubbard. Every-Day Butterflies. Boston, New York, 1899. 158-9. Web. Google Book Search. 15 Aug 2009.

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