Linked from
The 15 pages that link to Monarch butterfly, each with the reason it gives.
HerbivoreBroader topic: Its larvae tolerate milkweed toxins and retain them as a defense.
LepidopteraBroader topic: Its migration and chemical defense make it a prominent butterfly case.
Chemical defenseBroader topic: Its acquired toxins make it distasteful or harmful to many predators.
Diurnal animalBroader topic: Monarchs fly and feed during daylight, including during migration.