What are 'Nairobi flies', the skin-burning insects infecting students in Sikkim?

Over a hundred students of a Sikkim engineering college recently suffered severe skin infections due to 'Nairobi flies'. The small, beetle-like insects, which are orange and black in colour, thrive in areas with high rainfall. Health officials said these flies don't bite, but if disturbed while sitting on anyone's skin, they release potent acidic substance 'pederin' that causes burns.