Status, Distribution & Conservation

The Monarch Butterfly, Danaus plexippus L., in Canada


The Monarch butterfly, Danaus plexippus (L.), is the only species of the family Danaidae found in Canada (Monroe 1978; Scott 1986). The distribution of both the obligate larval hostplants, the Milkweeds (genus Asclepias), and the breeding range of the Monarch butterfly in Canada correspond quite closely to the Dfb zone (Humid microthermal climatic zone) of the Köppen climate and vegetation classification scheme described by Ackerman (1941; see also Fig. 3.1, pp. 89 of Scudder 1978; Appendix A). Monarch butterfly populations that enter Canada are distinct, with the large, expansive eastern population found everywhere east of the Rockies, and the small western population found only in the interior of British Columbia. The breeding distribution, and the distribution of known strays that range far beyond the range of the obligate hostplants, is given in Figure 1.

Eastern Population

Monarchs are casual non-breeding strays along the south coast of Newfoundland but have not been recorded from Labrador (Morris 1985; H. Clase and C. Majka, pers. comm.). In New Brunswick, the Monarch is recorded as having two broods but is considered a rare migrant which is not found every year (Thomas 1995). C. Majka (pers. comm.) suggests that the Monarch breeds in Nova Scotia as they can be quite common along the Bay of Fundy, especially during the fall migration, however, there are no published breeding records. Ferguson (1955) states that Monarchs were seen daily in the spring and again in the fall of 1949 and that 236 fall migrants were recorded over a six day period at Lunenburg Co. in that same year which also suggests that Monarchs do breed in Nova Scotia in some years. The Monarch is recorded from Prince Edward Island but is considered to be very rare (C. Majka, pers. comm.).

Monarchs from the eastern North American population are most common in southern Ontario and possibly southwestern Quebec where the larval hostplants are most abundant. Across the prairies from northwestern Ontario through to Alberta, the Monarch breeds in a relatively thin band between the Canada-U. S. border (49° N) and approximately 52° N. In the prairie provinces, the Monarch is most common in Manitoba where it occurs every year (Klassen et al. 1989), is uncommon to rare in Saskatchewan although relatively common in some years (Hooper 1973), relatively uncommon in southeast Alberta (Bird et al. 1995) but rare elsewhere in the province (N. Kondla, pers. comm.). Urquhart & Urquhart (1977; 1979a) report the Monarch as rare from Alberta with only scattered records for the prairies.

Western Population

The western population of Monarchs breeds in Canada only in the interior of British Columbia between the Rocky and Coastal mountain ranges up to about 52° N latitude with occasional strays being recorded from further north and from the Victoria/Vancouver area where they've been reported to breed on garden milkweeds (C. Guppy, pers. comm.). Guppy has recorded larvae in late June in the Similkamen Valley (49° N), Okanagan Valley (49-50° N), and Thompson River Valley (51.5° N) and considers it to be relatively common in the Okanagan Valley, rare elsewhere and very rare on the coast (C. Guppy, pers. comm.). Urquhart & Urquhart (1977; 1979a) report few butterflies in B.C. C. Guppy suggests that less than 1% of the Monarchs found at California overwintering roosts are Canadian in origin (pers. comm.).