Japanese beetle vs scarabaean

Japanese beetle and scarabaean both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese beetle	Yes	No	No	No
scarabaean	Yes	No	No	No

As nouns, scarabaean is a hypernym of Japanese beetle; that is, scarabaean is a word with a broader meaning than Japanese beetle:

Japanese beetle: small metallic green and brown beetle native to eastern Asia; serious plant pest in North America
scarabaean: any of numerous species of stout-bodied beetles having heads with horny spikes

Other hypernyms of Japanese beetle include scarabaeid, scarabaeid beetle.

Japanese beetle (noun)	scarabaean (noun)
small metallic green and brown beetle native to eastern Asia; serious plant pest in North America	any of numerous species of stout-bodied beetles having heads with horny spikes