The term 'insect-eating songbird' can be summarized by two crossword solutions: WREN (4 letters) and Vireo (5 letters). Wrens are small, brown birds that are found in many parts of the world. They have a loud, melodious song and feed mainly on insects. Vireos are a family of small passerine birds found in North and South America. They are typically greenish in color and have a distinctive song. Both wrens and vireos are insectivorous songbirds.