butterflies in one's stomach

Fluttering sensations caused by a feeling of nervous anticipation. For example, I always get butterflies in my stomach before making a speech. This term likens a nervous feeling to that resulting from swallowing live butterflies that fly about inside one. [c. 1900]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.