May bug vs melolonthid beetle

May bug and melolonthid beetle both are nouns.

Word	Noun	Adjective	Verb	Adverb
May bug	Yes	No	No	No
melolonthid beetle	Yes	No	No	No

As nouns, melolonthid beetle is a hypernym of May bug; that is, melolonthid beetle is a word with a broader meaning than May bug:

May bug: any of various large European beetles destructive to vegetation as both larvae and adult
melolonthid beetle: any of various beetles of the family (or subfamily) Melolonthidae

May bug (noun)	melolonthid beetle (noun)
any of various large European beetles destructive to vegetation as both larvae and adult	any of various beetles of the family (or subfamily) Melolonthidae
any of various large usually brown North American leaf-eating beetles common in late spring; the larvae feed on roots of grasses etc.