If your carefully tended crop of beans ever comes under attack from caterpillars, you should know it's not totally helpless. In fact, a cavalry of caterpillar-munching wasps may already be on their way. Bean plants have a remarkable ability to summon wasps from thin air when caterpillars attack, and now, scientists have figured out exactly how they do it. Humans have cultivated the common bean plant species, Phaseolus vulgaris , to give us much-loved varieties such as kidney beans, black beans,