June bug vs scarabaean

June bug and scarabaean both are nouns.

Word	Noun	Adjective	Verb	Adverb
June bug	Yes	No	No	No
scarabaean	Yes	No	No	No

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

June bug: any of various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.
scarabaean: any of numerous species of stout-bodied beetles having heads with horny spikes

Other hypernyms of June bug include scarabaeid, scarabaeid beetle.

June bug (noun)	scarabaean (noun)
any of various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.	any of numerous species of stout-bodied beetles having heads with horny spikes