Incorporating the qualities of an insect, often negative, into an adjective is an effective way to emphasize a point. Numerous figures of speech stem from our relationships to insects. He was so gentle he would never hurt a fly. She has a bee in her bonnet. I feel lousy.
Some expressions use an insect for no apparent reason or for contrived implication.
I had butterflies in my stomach. Shop at a flea market. Put a bug in his ear. Since I was knee high to a grasshopper. She's cute as a bug's ear.