Exercise protects mosquitofish from UV-B rays.

Since the invention of the internal combustion engine, traffic jams have become an inevitable part of life. ‘One of the problems faced by any transportation system is dealing with changes in traffic congestion’, says Tanya Latty, from the University of Sydney, Australia. ‘Sometimes there are simply more cars on the road than the system can handle’, she explains.And ants frequently face the same dilemma as they scurry along wellestablished odour superhighways that are continually reinforced by use as they forage. However, Latty explains, ‘Food resources can change in quality’, causing congestion as the determined insects have to respond to a change in circumstances. Knowing that the creatures of habit are almost as wedded to their tried and tested routes as we are to tarmac, Latty and Madeleine Beekman wondered whether Argentine ants can track changes in food quality and, if so,whether they could adjust their transport networks to make the most of changes in their circumstances.