Viability selection by invertebrate predators in the polyphenic black scavenger fly Sepsis thoracica

Males of the black scavenger fly Sepsis thoracica, which breeds in livestock dung, are either small and black or large and amber. In trying to understand the evolution of this rare phenomenon, we confronted flies of different sizes and colors with invertebrate predators in different backgrounds. We found that generally larger individuals survived better and that their coloration played a secondary role. Predation cannot be the primary cause of the male dimorphism.