Scientists have developed a fast, cheap and reliable technique that vastly improves the chances of successfully reintroducing the endangered large blue butterfly to the UK. The test can tell the difference between two ant species that look virtually identical to us, but which are far from it — at least from the rare butterfly\'s point of view.          One type of ant is essential for the large blue\'s survival, while the other spells almost certain death. \'The ants in question — two species of Myrmica red ants — look very similar and even trained ant taxonomists have trouble distinguishing between the two,\' says Rhian Guillem from the University of Sheffield, who led the study. \'And there are only a handful of people who can do this in the UK.\' But scientists are discovering that even if two ant species look alike, the chemical compounds on their bodies can be very different. It\'s this difference that can be used to tell the two species of red ant apart.