Chlorophyll breaks down, so other pigments visible. Stem side of abscission zone gets cork cells to seal stem after leaf falls. Wind breaks connections of few xylem cells and leaves fall. Leaves attract, capture, digest prey Passive trap in pitcher plant. Bug can't crawl back out.
Body disintegrates in water at bottom.
Some insect larvae can live in bottom water of pitcher plant, though. Active trap on Venus flytrap. 3 trigger hairs cause leaves to snap shut.