Poecilognathus relativitae, originally known as Phthiria relativitae, is a species of fly of the family Bombyliidae, subfamily Phthiriinae, that is found in California. It was discovered by Neal Evenhuis, who named it as a pun on the "theory of relativity".
Subsequent analysis revealed that the insect is not of the genus Phthiria, and it was renamed.