Monarch Butterfly, the only butterfly of the family Danaidae (order Lepidoptera) found in Canada. Because of its migratory habits, it is possibly the best-known, most publicized migratory butterfly. Found in every province and territory, it is only numerous where the host plant milkweed (Asclepias spp.) grows. Its large size, orange and black coloration and slow, sailing flight make it a familiar butterfly of such areas.
The spring migration northwards into Canada is accomplished by the progressive advancement of individuals of successive generations. The legendary fall migration southwards is undertaken by adults of the final summer brood. Monarchs born W of the Rockies overwinter in California; those from central and eastern N America in central Mexico. After 40 years of research, the first Mexican wintering site was discovered in 1974 by Frederick Urquhart of U of T.
All monarchs were originally thought to contain a poison absorbed from their caterpillars' host plant. Recent research on monarchs suggests that since only certain species of milkweed contain these deadly cardiac glycosides, butterflies originating from caterpillars reared on such nonpoisonous milkweeds, eg, common milkweed (A. syriaca) and showy milkweed (A. speciosa) are no longer thought toxic.