Half-moon hairstreak (Satyrium semiluna) COSEWIC assessment and status report: chapter 5
Species information
Name and classification
Satyrium semiluna Klots, known until recently as S. fuliginosum (W.H. Edwards, 1861), is a hairstreak butterfly of the family Lycaenidae. Mattoon and Austin (1998) provide a recent taxonomic review and recognize five subspecies in two phenotypically distinct groups. The ‘fuliginosum’ group was considered to consist of subspecies albolineatum Mattoon and Austin, 1998; fuliginosum, and tildeni Mattoon & Austin, 1998. The ‘semiluna’ group was considered to consist of subspecies maculadistinctum Mattoon & Austin, 1998 and semiluna Klots, 1930.
Recent Canadian literature (Bird et al. 1995, Layberry et al. 1998, Guppy and Shepard 2001) consistently places the Alberta population in the subspecies semiluna. This interpretation is also advanced by Kondla (2003a, 2004b), although the adults are noticeably smaller than individuals from Idaho, southern Montana and Wyoming. Taxonomic placement of the British Columbia populations at the subspecies level is variable in the literature. Layberry et al. (1998) treat these as subspecies fuliginosum while Guppy and Shepard (2001) treat these as subspecies semiluna. Pyle (2002) quotes A. Warren as considering them as a “probably undescribed” subspecies. Kondla (2003b) also considers the British Columbia populations to be an undescribed entity.
Recent work by Warren (2005) resulted in the separation of S. semiluna from S. fuliginosa, with S. semiluna being given formal species status. This split is based on the fact that “males from all populations of S. semiluna have forewing stigmata, which vary from being vestigial to well-developed, while males of S. fuliginosa lack any trace of forewing stigmata” (Warren, 2005). The stigmata are patches of specialized scent scales that have recently been shown to be important in mating (D. Lafontaine, pers. comm.). Consequently, the former S. fuliginosa has been divided into two species (Warren, 2005) with true S. fuliginosa restricted to California and S. semiluna found everywhere else (D. Lafontaine, pers. comm.). Both populations in Canada are now recognized as being S. semiluna (A. Warren, pers. comm.). The British Columbia population may be a separate subspecies from typical S. semiluna which was described from northern Wyoming, but there is no subspecific name applied to the British Columbia form (D. Lafontaine, pers. comm.).
The English common name, Half-moon Hairstreak, is used in this report as the species is named for the type locality, Half-Moon Ranch in Teton County, Wyoming (A. Warren, pers. comm.). The French common name ‘Porte-queue demi-lune’ is recommended (J.-F. Landry, pers. comm.).
Morphological description
The Half-moon Hairstreak is a small, drab butterfly that looks predominantly brownish or blackish brown on the dorsal wing surfaces. The colour depends on sex, subspecies, amount of flight wear and age of museum specimens. Unlike many other species of hairstreaks, there are no tails on the hindwings.
Figure 1. Dorsal and ventral views of the Alberta (Waterton Lakes National Park) and British Columbia (vicinity of White lake) entities in comparison to each other.
Scale is lifesize.
Description of Figure 1
Figure 1 illustrates Alberta and British Columbia males. Comparative illustrations showing S. fuliginosa and Canadian females are provided in Kondla (2003b).
Males of the Alberta population are very small, with a wingspan of 25 mm or less. The dorsal wing surface is dark brown which fades to lighter brown with age. Males have a conspicuous dark stigma (patch with androconial scales) on the dorsal surface of the forewing. The undersides of males are medium brown with grey overscaling along the distal wing margins. Large black spots, slightly edged with white scaling, are present in the postmedial area of the ventral surface of the forewing. The black postmedial spotting on the dorsal side of the hindwings is much reduced. The submarginal areas of the undersides of the wings are featureless or have very faint markings. Females are larger and are paler and greyer on the ventral side than males
Males of the British Columbia population of the Half-moon Hairstreak have a wingspan of 30 mm or more and are conspicuously larger than their Alberta counterparts. The dorsal wing colour is a dark grey-brown that appears blackish when fresh. The dorsal colour fades to brown with age. The stigma on the dorsal surface of the forewing of most individuals is inconspicuous and less cleanly defined than in individuals of the Alberta population. Male undersides are more conspicuously spotted than in the Alberta population. This increased maculation includes more distinct marginal spotting and a more conspicuous dark bar at the forewing cell end. Females differ from males in the same manner as their Alberta counterparts.
Adult Half-moon Hairstreaks can be confused with another lycaenid butterfly that flies in the same areas and overlaps in flight period. This butterfly is Aricia icarioides, Icarioides Blue or Boisduval’s Blue (also placed in the genera Icaricia or Plebejus by various authors). This identification confusion is limited to ventral views because males of Aricia icarioides are blue on the dorsal wing surface and even female A. icarioides normally have at least some basal blue on the dorsal surfaces of the wings.
The eggs of S. fuliginosa, which may actually refer to S. semiluna, are described by Scott (1986a) as greenish white. Scott (1992) provides further details on the appearance of the egg and notes that some eggs are tan coloured, possibly as a consequence of age. Last-instar larvae are described by Ballmer and Pratt (1988). They note that the larva superficially resembles that of Aricia icarioides. The larva is reported as having a light green ground colour with whitish lateral chevrons and a dark brown head.
Genetic description
Gene flow between the British Columbia and Waterton Lakes populations is highly unlikely because of substantial geographical separation and ecological barriers. The Guelph Centre for DNA Barcoding has assembled a segment of the mitochondrial DNA sequences of cytochrome C oxidase from ten specimens of S. semiluna (four from the White Lake basin in British Columbia, two from Waterton Lakes National Park in Alberta and four from Kittitas County in Washington State). The nucleotide sequence for all ten specimens was identical. This result does not support, but neither does it refute, the hypothesis that differences in the appearance of adults and structural differences in the male androconial patch may be indicative of differences in genetic structure between the Alberta and the British Columbia populations, because the analysis does not resolve recent divergences (F. Sperling, pers. comm.).
Designatable units
There is some evidence that the two Canadian populations may be taxonomically distinct, but there are no subspecies level names for the populations, and more work needs to be done on this aspect. The observed morphological differences may be indicative of two different entities, or they may reflect plasticity of certain characteristics when the species occupies different habitats.
There is a significant geographical disjunction between the two populations in Canada, which also extends well south of the Canadian border. There is no opportunity for exchange of individuals between the Alberta and British Columbia populations. The populations are separated by a linear distance of approximately 400 km, most of which consists of habitats that are not suitable for the species. These populations may not appear to be biogeographically distinct if one considers all of the cordilleran area in southwestern Canada to be homogeneous, but the biogeographic and ecological environments of the south Okanagan area of British Columbia and southwestern Alberta are different. In addition, there are large areas of unsuitable high elevation habitat west and east of the Rocky Mountains both in Canada and in the United States. Although the Alberta and British Columbia populations occur in different ecological situations and are isolated from each other, they occur within the Southern Mountain ecozone.
The Alberta and British Columbia populations are subject to different land use regimes and threats. The Alberta population is located in a national park where anthropogenic threats are limited, although the population is exposed to stochastic natural processes and is subject to the effects of knapweed invasion and control. The British Columbia population occurs at a number of sites which are subject to a range of land uses that may threaten the persistence of the butterfly at these sites. Its habitat is also subject to invasion by alien plant species.
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