Without insects, our world would be a very different place

Imagine for a moment, a world without insects... "Wonderful!", you say, "Finally I can explore the great outdoors unbothered by all those nasty creepy-crawlies! Picnics without ants! Apples without worms! Camping without mosquito bites! Paradise! Where do I sign up?" Before you get too excited, consider this. Without insects, our world would be a very different place. If insects didn't play their roles as pollinators and as food sources for other animals, our food supply and selection would be drastically reduced. As a result, you might have trouble putting together that "ant-free picnic" you were so looking forward to. Likewise, a pleasant camping spot might be difficult to come by in a world full of animal waste and dead plants and animals that would exist without insects to help break them down.

While it's true that some insects - like those bloodsucking mosquitoes or plant-eating pests - directly harm humans, the vast majority don't. Rather, they're all a vital part of this planet's ecology. They provide food for other animals (including humans in some cultures), recycle natural materials, and help plants to reproduce. They even create products we use every day, such as silk and honey. On a scientific level, insects provide systems for exploring and modeling human body processes. So, you see, insects help us to better understand ourselves and the world around us.

Source: The Manduca Project
http://insected.arizona.edu/manduca/Insects.html