lady beetle vs ladybird

lady beetle and ladybird both are nouns.

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

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

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

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

lady beetle (noun)	ladybird (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