Adaptation

Venus fly traps adapted to be able to ingest insects as an adaptation to environments where there was a poor nutrient supply in the soil.  Natural selection favored venus fly traps with a quicker reaction time and wide leaves that move their trap and stalks in ways that make it hard for the insect to escape.  They've acquired trigger hairs on the inside of their leaves that help them differentiate between insects and other things such as rain droplets.  Their digestive glands allow them to digest the insect once they've trapped it.

image: http://www.carnivorous--plants.com/graphics/venus-fly-trap.jpg

info: http://en.wikipedia.org/wiki/Venus_fly_trap