monarch vs Danaus plexippus

monarch and Danaus plexippus both are nouns.

Word	Noun	Adjective	Verb	Adverb
monarch	Yes	No	No	No
Danaus plexippus	Yes	No	No	No

As nouns, monarch and Danaus plexippus are synonyms defined as:

monarch and Danaus plexippus: large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed

Other synonyms of monarch include milkweed butterfly, monarch butterfly.

monarch (noun)	Danaus plexippus (noun)
large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed	large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed
a nation's ruler or head of state usually by hereditary right