June beetle vs June bug

June beetle and June bug both are nouns.

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

As nouns, June beetle and June bug are synonyms defined as:

June beetle and 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.

Other synonyms of June beetle include May beetle, May bug.

June beetle (noun)	June bug (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 various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.