From Nature:
Next time you dismiss insects as mere creepy-crawlies, ponder for a while on what life would be like without them. Our six-legged friends might be more valuable than you think — research estimates that they’re worth at least a staggering $57 billion to the US economy every year. By far the greatest direct contribution of insects comes from their role as food for birds, game and fish. Given the overall value to the US economy of the recreation industries of hunting, fishing and birdwatching, and the proportion of species involved that eat insects, these industries would be almost $50 billion worse off each year without them. Insects also save farmers some $4.5 billion each year by gobbling up pests on dozens of different crops, and a cool $3 billion by pollinating many different fruits and vegetables. The humble dung beetle chips in with savings worth $380 million, by keeping cowpats out of the way of parasitic flies and saving valuable cattle from infections.
More here.