A food web is a way of seeing how energy is transferred from organism to organism. All living things need energy. They use it to move, to grow, to reproduce. That energy has to come from someplace. Drawing a food web is a great way to get an idea of how that energy is captured by producers, and passed from organism to organism. It helps us see that even things that we usually don't like, such as weeds and mosquitos, play an important role in the ecosystem.