阅读理解 Ants have a reputation for strength, organization and teamwork．But researchers have now discovered that a key secret to the success of ants is their ability to identify the importance of age in the work place． A study of Central American leaf-cutter ants has shown that the younger and stronger members are given the toughest job of cutting through the; leaves they harvest．Their sharp young teeth do this job effectively, but as they get older their teeth become relatively worn and blunt． But rather than being retired or abandoned by the group, the ageing ants are given a new role more suited to their physical abilities．They become carriers and transport the leaves back to the kingdom where they are harvested for food． The findings by researchers from the University of Oregon and the Oregon State University support previous research showing the survival of a leaf-cutter kingdom depends on the efficiency(效率)of its workers． "Cutting leaves is hard work," said Dr．Robert Schofield, who led the research team．"Much of the cutting is done with a V-shaped blade(刀片)between teeth on their jaws．This blade starts out as sharp as the sharpest razor blade that humans have developed．" But over time the teeth become blunter and the cutting job slows down．The team estimated that, because of this age-related wear, a colony(蚁群)spent twice the energy cutting leaves than it would if all the ants had sharp blades．Its findings support the idea that wear and break can be significant problems for insects as well as larger animals． Like humans, leaf-cutter ants recognize that older members of the group can still make a worthwhile contribution to society．"This study shows an advantage of social living that we are familiar with," said Dr．Schofield． | 
