Myrmarachne bakeri Banks 1930 is a polymorphic, generalized ant-mimicking jumping spider. In this study, variation in its polymorphic characters was observed and described. Myrmarachne bakeri varies in color, glossiness and patterns; and differs from other polymorphic ant-like spiders because it becomes polymorphic before adulthood. Morphological changes appear to have no set archetype, and few spiders revert to morphs previously observed. Polymorphism is widespread in Myrmarachne, but to date no species has been shown to exhibit the type of variation found in M. bakeri. © 2010 The American Arachnological Society.