ladybird beetle vs ladybug

ladybird beetle and ladybug both are nouns.

Word	Noun	Adjective	Verb	Adverb
ladybird beetle	Yes	No	No	No
ladybug	Yes	No	No	No

As nouns, ladybird beetle and ladybug are synonyms defined as:

ladybird beetle and ladybug: small round bright-colored and spotted beetle that usually feeds on aphids and other insect pests

Other synonyms of ladybird beetle include lady beetle, ladybeetle, ladybird.

ladybird beetle (noun)	ladybug (noun)
small round bright-colored and spotted beetle that usually feeds on aphids and other insect pests	small round bright-colored and spotted beetle that usually feeds on aphids and other insect pests