Scientific Name: Satyrium semiluna
Taxonomy Group: Arthropods
Range: British Columbia, Alberta
Last COSEWIC Assessment: April 2006
Last COSEWIC Designation: Endangered
SARA Status: Schedule 1, Endangered
Image of Half-moon Hairstreak
The two Canadian populations may belong to separate subspecies, but at present these populations are not named at the subspecies level.
The Half-moon Hairstreak is a small, drab butterfly. The individuals of the two Canadian populations have several different physical characteristics. For instance, males of the British Columbia population have a wingspan of 30 mm or more and are conspicuously larger than their counterparts from Alberta, where males have a wingspan of 25 mm. Predominantly brown or blackish brown on the dorsal wing surfaces, with varying quantities of black spots, slightly edged with white scaling, the colour of Half-moon Hairstreak depends on sex, subspecies, amount of flight wear, and age of museum specimens. Unlike many other species of hairstreaks, the Half-moon Hairstreak has no “tail” on the hindwing. In both Alberta and British Columbia, females are larger and are paler and greyer on the ventral side than the males. The eggs are greenish white, but some are tan coloured, possibly as a consequence of age. The caterpillar has a light green ground colour with whitish lateral chevrons and a dark brown head. Adult Half-moon Hairstreaks can be confused with Boisduval’s blue, a related butterfly that flies in the same areas and overlaps in flight period. Male Boisduval’s blues are blue on the dorsal wing surface and the females also normally have at least some basal blue on the dorsal surfaces of the wings.
Distribution and Population
The range of the Half-moon Hairstreak extends from extreme southern interior British Columbia south to central California and east to eastern Wyoming and northern Texas. In Canada, the species, which is restricted to the southwestern part of the country, occurs as two disjunct populations. The British Columbia population is known from six locations in the southern Okanagan Valley, from the Canada-United States border north to White Lake. This population is contiguous with populations in Washington. On the east side of the Rocky Mountains, Alberta has one known population, in Waterton Lakes National Park of Canada. This population is disjunct from the nearest known populations in the United States. In 2003, the Alberta population of the Half-moon Hairstreak was thought to be anywhere from several thousand to fewer than 10 000 adults. In 2004, only 250 adults were observed in this population. The reasons for this dramatic population decline are unknown, but it may have been caused by an unusually late killing frost in the area in the spring of 2004. The size of the British Columbia population is unknown, but could include 5000 to 15 000 adults, although this is a very approximate estimate. Population trends are unknown. The likelihood of a rescue effect from the United States to the Alberta population is very low because there are no known locations nearby. However, there is a possibility of a rescue effect to the British Columbia population. There are Half-moon Hairstreak populations in Washington a short distance from the British Columbia population.
In British Columbia, populations of Half-moon Hairstreak have been found at elevations of 600 to 1100 m in sagebrush/bluebunch wheatgrass habitat where silky lupine is present. The butterflies were found in areas that had reduced relief in comparison to surrounding steeper areas. The single Alberta population is restricted to grassland habitat with abundant lupines at 1300 m elevation in Waterton Lakes National Park.
The food plants used by Half-moon Hairstreak caterpillars (larvae) have not been confirmed in Canada, but lupines are thought to be used because of the association of the butterfly with lupines at all known sites in Canada and the confirmed use of lupines as the host plant in the United States. This species has one annual brood. Eggs are laid on lupines or in the leaf litter at the base of the plants, and the species overwinters in this form. The larval stage therefore occurs in spring, and adults emerge in the late spring or early summer. Adults of the British Columbia population have been found from late May to early July, and adults have been found in Alberta mainly in the last two weeks of July. In both provinces, adults were active during much of the daylight period. The likely association of the caterpillars with ants may be a significant factor in the biology of this species. Many of the caterpillars in this family of butterflies secrete a nutritious liquid that is consumed by attendant ants. In return, the ants guard the caterpillars from attacks by predators and parasites. This mutual assistance relationship could be a decisive factor in the distribution of the species, and it may partially determine the butterfly’s habitat requirements, since ants have specific habitat requirements that may differ from the butterfly’s habitat requirements. Thus two interacting sets of requirements may determine the suitability of an area for the Half-moon Hairstreak.
Both of the Canadian populations of the Half-moon Hairstreak are threatened by habitat loss and degradation. In British Columbia, the species occurs in an area that is under severe development pressure. In fact, its populations are subject to a wide variety of human activities that could reduce or extirpate local populations. Intensive livestock grazing is one of the most serious threats, particularly on private land where there are no restrictions to prevent overgrazing. Conversion of sagebrush grasslands to agriculture and habitat loss to development are considered to be other serious threats to these populations. For example, the amount of habitat at one of the Richter Pass locations may be reduced in the future through the expansion of an aggregate pit. In addition, the human population is growing at a rapid rate in the area and this is expected to continue. In parallel with increases in the human population, residential housing and road construction continue to consume habitat on Anarchist Mountain and housing expansion is very much an ongoing threat in the south Okanagan area. Finally, native grassland habitat is also being converted to intensive agricultural uses, including vineyards, which are undergoing rapid expansion in the area. In Alberta, the population is located in a national park where human threats are limited. However, the population may be limited primarily by flooding and possibly by severe spring frosts. This population is also threatened by an invasion of spotted knapweed. Continuation of the spread of spotted knapweed will alter the habitat either directly through competition for resources or as a consequence of weed control measures. Invasive weeds also pose a threat in British Columbia.
Federal ProtectionThe Half-moon Hairstreak is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.
The population of this species that occurs in Waterton Lakes National Park of Canada, in Alberta, is protected under the Canada National Parks Act. The British Colombia population is not protected by any provincial law in British Columbia.
Provincial and Territorial Protection
Status of Recovery Planning
Recovery Strategies :
Name Recovery Strategy for the Half-moon Hairstreak (Satyrium semiluna) in Canada
Status Final posting on SAR registry
South Okanagan Invertebrates at Risk Recovery Team
Orville Dyer - Chair/Contact - Government of BC
Phone: 250-490-8244 Send Email
Jennifer Heron - Chair/Contact - Government of BC
Phone: 604-222-6759 Fax: 604-660-1849 Send Email
PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.
11 record(s) found.
- COSEWIC Status Reports (1 record(s) found.)
- COSEWIC Assessments (1 record(s) found.)
- Response Statements (1 record(s) found.)
- Recovery Strategies (1 record(s) found.)
- Action Plans (1 record(s) found.)
- Orders (2 record(s) found.)
- COSEWIC Annual Reports (1 record(s) found.)
- Consultation Documents (1 record(s) found.)
- Critical Habitat Descriptions in the Canada Gazette (1 record(s) found.)
- Recovery Document Posting Plans (1 record(s) found.)
COSEWIC Status Reports
COSEWIC Annual Reports
COSEWIC Annual Report - 2006 (2006)2006 Annual Report to the The Minister of the Environment and the Canadian Endangered Species Conservation Council (CESCC) from the Committee on the Status of Endangered Wildlife in Canada.
Critical Habitat Descriptions in the Canada Gazette
Recovery Document Posting Plans
- Date modified: