Three species of butterflies are known to hybridize within the Niobrara River Valley. They are the Red Spotted Purple (Limenitis arthemis astyanax), Eastern Viceroy (Limenitis [Basilarchia] archippus), and Weidemeyer’s Admiral (Limenitis (Basilarchia) weidemeyer). Another species, White Admiral (Limenitis arthemis arthemis) is known to interbreed with the Red Spotted Purple although none have been documented in the Niobrara River Valley.
Their offspring include Rubidus, a cross between the Red Spotted Purple and Eastern Viceroy and a cross between Weidemeyer’s Admiral and the Red Spotted Purple. There is a possibility that a hybrid between the Red Spotted Purple and White Admiral exists within the valley, though none have been documented.