Population Fluctuations of the Schaus Swallowtail (Lepidoptera: Papilionidae) on the Islands of Biscayne Bay, Florida, with Comments on the Bahaman Swallowtail

Abstract

Censuses of the Schaus swallowtail butterfly (Heraclides (= Papilio) aristodemus ponceanus (Schaus)), a federally listed threatened species, were conducted from 1979 to 1982 on islands in Biscayne Bay, southern Florida. The population size was small during 1979 and 1980, but adults were widely distributed in suitable habitat. Emergence season was similar in both years, from late April to late June. Numbers of the Schaus swallowtail were lower in 1981, and the emergence period seemed to be retarded, probably due to the very dry winter and spring. Following the wet winter of 1981-1982, the largest numbers of adult Schaus swallowtails since 1972 were recorded. It appears that the severity of the winter dry season may determine the population size of this species in southern Florida. In combination with results of previous censuses, these data provide a continuous eleven-year record of Schaus swallowtail population fluctuations on the Biscayne Bay islands. Human disturbances, especially habitat destruction, have reduced the numbers and range of the Schaus swallowtail, so the butterflies on these islands presently form the nucleus of its population in the United States. The Bahaman swallowtail (Heraclides (= Papilio) andraemon bonhotei (Sharpe)) was not observed during the censuses, and we conclude that it is not presently established on the islands we studied.