G.B. Edwards paper (1980) describes the resemblance of red jumpers to wingless mutillid (velvet ants) wasp females. P. cardinalis females mature in autumn and it is striking how many natural objects in their sandy, xeric habitat are also red. The list includes the basal portion of the andropogon grasses on which the spiders are often found, blueberry foliage, maple leaves scattered on the ground and even a dark red fungus. Perhaps the most strikingly red inhabitants are the British Soldier lichens (Cladonia cristatella). So the cardinal jumper's seemingly high profile color is right at home in their chosen habitat.

Images from video at::
Natural History Services - Jumping Spiders