"The corn rootworm is a pest that lays eggs in cornfields so its larvae will come up the next year and feast on the roots. Farmers have evaded it by rotating crops so what was a cornfield one year will be soybeans the next. By the 1990s, however, the strategy wasn’t working: rootworms had changed—instead of hatching every year, one species was hatching every other year, to be there when the corn returned. Another was now laying eggs in soybean fields, so the larvae would hatch under corn."