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Recovery Strategy for Multi-Species at Risk in Maritime Meadows associated with Garry Oak Ecosystems in Canada (Proposed)


Species Descriptions

1.11 Taylor's checkerspot Euphydryas editha taylori

Common Name: Taylor's checkerspot

Scientific Name: Euphydryas editha taylori (W. H. Edwards)

Status: Endangered

Reason for designation: This butterfly has undergone significant range-wide reductions in population size. Until recently, it persisted at one site in Canada in coastal grasslands. Much of its habitat has been destroyed, and introduced invasive plants have eliminated its larval host plant in most of the remaining site.

Canadian Occurrence: British Columbia

Status history: Designated Endangered in November 2000. Assessment based on a new status report.

1.11.1 The species

Taylor's checkerspot is a medium-size butterfly. The upper wing surfaces have distinct alternate black and orange bands. Wing undersides show a pattern of orange, white, red, pale cream and black-checkered bands outlined with black. Checkered bands are parallel to the black thorax and abdomen. The front wings have rounded tips. Males are slightly smaller than females.

Caterpillars are black with orange bands. Eggs are pale yellow and transparent. Euphydryas editha taylori is a well-delineated taxon as described in the COSEWIC Status report (Shepard 2000c).

1.11.2 Distribution

The current global range consists of fifteen known populations in Clallum County and the south Puget Sound (Washington) (S1), and the Willamette Valley (Oregon) (S1) (Figure 2).

In Canada, Taylor's checkerspot is known historically from 22 naturally fragmented populations: fifteen sites in the greater Victoria area, three sites from Mill Bay to Duncan, three sites on Hornby Island and one near Courtenay (Figure 2). Records date from 1887 to 1995. The species is currently listed as Endangered (2000), although recent surveys in 2001 and 2003 of the last known sites confirmed the species is likely extirpated from Canada (Miskelly 2003). However, in 2005, 15 individuals were found on Denman Island, near Courtenay on Vancouver Island (Jennifer Heron, pers. comm., 2005).

Figure 2. Global and Canadian distribution of Taylor's checkerspot
(Extirpated populations shown as triangles)
Figure 2. Global and Canadian distribution of Taylor's checkerspot Extirpated populations shown as triangles)

1.11.3 Population and distribution trend

Many of the populations in the Victoria area persisted until the 1950s except the Beacon Hill Park population, which was likely extirpated by the early 1930s. In 1989, only one population remained, which was in a powerline right-of-way 3 km southwest of Mill Bay (Shepard 2000c), which was also extirpated by 1995 (Shepard 2000a). In 1995, several populations were found on Hornby Island, were known to be extant in 1996 (Shepard 1995; Shepard 2000b; 2000c), but were thought to be extirpated by 2001 (Guppy and Fischer 2001).

Although trends are not documented specifically for Taylor's checkerspot habitat, Garry oak and associated ecosystems have declined substantially. Fire suppression and conifer encroachment into areas of water seepage and deeper soil, coupled with drought, may have extirpated the Helliwell Park population on Hornby Island.

In Washington State, population sizes are unknown. The two populations in Oregon state are estimated at 1000 (Vaughan and Black 2002b) and 500 (Black pers. comm. 2004). Historic Canadian populations numbered 1100 at Hornby Island (1996) and 1000 at Mill Bay (1989) (Shepard 2000c) but there is no indication of the former total number of individuals in Canada.

1.11.4 Biotic and abiotic features of habitat

Habitat descriptions for the Taylor's checkerspot are based on observations of the last known occupied locations cccc and current descriptions of sites with historic records. There are no completed habitat studies for this butterfly in Canada, although research is underway at the University of Victoria (Eastman et al. 2002).

Taylor's checkerspot requires non-forested habitats (Shepard 2000b; 2000c). Native ecosystem habitats are not necessarily required; areas cleared by human activities, such as powerline rights-of-way, can be suitable habitat (Vaughan and Black 2002b; Shepard 2000b; 2000c). Recent surveys in Washington have found thriving populations in new locations uncharacteristic of historic populations, including a site at 600m elevation in habitat that was formerly logged and burned with sheer cliffs interspersed with the native species oceanspray (Holodiscus discolor), ceanothus (Ceanothus sp.) and currants (Ribes spp.) (Miskelly pers. comm. 2004).

Foodplants of extant populations in the United States are ribwort plantain (Plantago lanceolata), harsh paintbrush (Castilleja hispida), large-flowered blue-eyed Mary (Collinsia grandiflora), sea blush (Plectritis congesta) and one record of dwarf owl-clover (Triphysaria pusilla) (Grosboll pers.comm. 2004, Potter pers. comm. 2003;2005). Taylor's checkerspot larvae may also use sea plantian (Plantago maritima), golden paintbrush (Castilleja levisecta), and possibly other owl-clover species (Murphy et al. 1983; Pelham, pers. comm. 2003).

It is unknown whether any populations in British Columbia used anything other than ribwort plantain (Plantago lanceolata) as a primary or secondary foodplant (Shepard 2000b; 2000c; Danby 1890). It is speculated that Taylor's checkerspot populations in British Columbia could have used the same, additional foodplants as those used by butterflies in Washington.

Nectar is not required for reproduction, but egg production in subspecies E. editha bayensis is dependent on available nectar sources, with up to double the number of eggs laid when nectar was abundant (Murphy et al. 1983). Important nectar sources for extant populations of Taylor's checkerspot in the United Statesinclude common camas (Camassia quamash), strawberries (Fragaria spp.), spring gold (Lomatium utriculatum), and sea blush (Plectritis congesta) (Potter pers. comm. 2003; Grosboll pers. comm. 2003; Ross pers. comm. 2003). Nectar plants for former British Columbia populations are not known.

This species is particularly vulnerable to invasion by exotic shrubs, which decreases the availability and amount of foodplants. Scotch broom (Cytisus scoparius) invasion of human-cleared habitat resulted in the extirpation of the population near Mill Bay, BC (Shepard 2000b; 2000c). Invasion was implicated in the extirpation of at least one Washington population, and may threaten one remaining population in Oregon (Vaughan and Black 2002b). The Bright Angel Provincial Park population, south of Duncan, British Columbia, was extirpated by subdivision development adjacent to the park, combined with increased native shrub growth within the park (Guppy, pers. comm. 2003).

1.11.5 Spatial requirements

In order to ensure long-term survival of a population, the required patch size is estimated to be 5 to 20 hectares of high quality habitat (abundant ribwort plantain [Plantago lanceolata] or harsh paintbrush [Castilleja hispida] and nectar sources). These figures are based on estimates of the areas occupied by historic populations (Guppy pers. comm. 2003). Several extant populations occupy areas of less than one hectare (Miskelly pers. obs. 2004).

1.11.6 Annual cycle

The related subspecies, Euphydryas editha bayensis, typically lays an initial mass of 130-180 eggs, with each female laying several batches of eggs of successively smaller numbers (Murphy et al. 1983). This is consistent with the size of clusters of first instar larvae observed at the Taylor's checkerspot site southwest of Mill Bay (Guppy pers. comm. 2003). The larvae hatch from eggs in May or early June and feed until they are in the late third instar and enter diapause.

Techniques of captive oviposition of checkerspots, with or without captive mating, are well known and easily implemented (eg. Murphy et al. 1983). In 1988/89, Guppy (pers. comm. 2003) successfully reared Taylor's checkerspot larvae, collected as second instar from near Mill Bay, BC. In 2004, Taylor's checkerspot rearing experiments were conducted using 20-40 larvae collected in Thurston and Clallum County, Oregon. A more rigorous rearing program for Taylor's checkerspot is scheduled to begin in 2005 (Potter pers. comm. 2005). There may be significant phenological differences between populations in Canada and the United States that suggest some degree of genetic divergence (Guppy pers. comm. to Miskelly 2004).

1.11.7 Ecological niche

There has been no research on the ecological role of this butterfly. The adults, when at high densities, may be significant pollinators of native spring flowers. The larvae are major herbivores of ribwort plantain when at high densities, and can completely strip off all leaves on plants in some patches (Guppy pers. comm. 2003). There is no evidence that this herbivory adversely affects the viability of plantain populations. Adults, larvae and pupae may serve as prey for insectivorous birds, small mammals, and predatory insects. However they contain iridoid glycosides (sequestered from their larval foodplants), and hence are not palatable to most predators. Eggs, larvae and pupae are likely to also function as hosts for insect parasitoids (van Nouhys and Hanski 2004).

1.11.8 Biologically limiting factors

Dispersal capabilities of Taylor's checkerspot have not been studied. Adults of subspecies E. editha bayensis and E. editha wrighti only move 200 to 300 feet under favourable environmental conditions even within patches of suitable habitat, but may disperse more widely under stress of drought or high densities, and have difficulty establishing new populations even when transplanted (Ehrlich 1961; Ehrlich et al. 1980; Harrison 1989; Murphy and White 1984). E. editha taylori appears to be less limited in dispersal abilities, and has been observed crossing forested areas and other barriers (Potter pers.comm. 2003; Vaughn pers. comm. 2003; Black pers. comm. 2004). Metapopulations of subspecies bayensis rely on a large, stable central population as a source to establish and stabilize peripheral populations (Harrison 1989). If new populations are re-established in Canada, distance between patches of suitable habitat may have a strong influence on dispersal potential. In some instances, populations of subspecies bayensis are very close to another and share very few individuals and did not rescue one another from extirpation (Hellmann et al. 2003, McLaughlin et al. 2002).

Larval starvation results when the foodplants, especially plantain, desiccate due to summer drought prior to the larvae entering diapause (Vaughan and Black 2002b). This is believed to be the main cause of mortality in this species. The effects of weather on larval success in reaching diapause, and on survival through diapause, has been demonstrated to be a key variable in determining adult population size and population persistence in the Californian subspecies bayensis (McLaughlin et al. 2002). Viable populations of other subspecies in California are around 1000 individuals (Ehrlich 1961; Hellmann et al. 2003) with smaller populations having greater susceptibility to extirpation by droughts or other stochastic events. However, even populations that numbered around 1000 individuals have become extirpated (Hellman pers. comm. 2005). Climate change is expected to increase rates of extinction for Taylor's checkerspot (McLaughlin et al. 2002) by limiting the variability of foodplants phenology.

Taylor's checkerspot larvae are actively feeding during the early spring when Btk is normally applied to control forest pests (Wagner and Miller 1995; Nealis pers. comm. 2003).