Researchers have discovered more about a world of selfless "soldier" aphids who risk their lives to defend nests from invaders. The insects also clean and mend the nests using a sticky secretion. But the substance comprises two thirds of their body mass, and many of them die from significant weight loss when carrying out their duties. John Bryden, research associate in the School of Biological Sciences at Royal Holloway, University of London, said: "We are interested in why animals are nice to each other - why they show social behaviour. This is puzzling because, in a fiercely competitive fight for resources, helping others seems like a fool's game."