Martialis heureka is a species of ant that was discovered in 2000 from the Amazon rainforest near Manaus, Brazil. It was described as a new species and placed as the sole member of a new subfamily, Martialinae. The generic name means "from Mars" and was given due to its unusual morphology, and the species epithet heureka indicates the surprising discovery. It belongs to the oldest known distinct lineage to have diverged from the ancestors of all other ants.
Like all members of the family Formicidae these ants have the distinctive elbowed antennae, prominent metapleural glands and a distinctive petiole. The ants however lack compound eyes, are pale in colour, and lead a subterranean life preying on small litter organisms. The workers have unusual, elongated mandibles that are distinctly basal in their features.
Based on the morphology the authors suggest that the ants lead an underground life, possibly foraging on the surface during the night. The first two specimens were found in soil core samples while another was found in leaf litter. They probably make use of pre-existing underground cavities as the legs do not show adaptations for digging.
Two specimens were first discovered by Manfred Verhaagh of the Staatliches Museum für Naturkunde in Karlsruhe, Germany in 2000, but they were damaged and it was only in 2003 that a new specimen was collected by Christian Rabeling, a graduate student of the University of Texas at Austin.
The aberrant features of this ant led Stefan P. Cover and Edward O. Wilson to comment that it was an ant that had to be from Mars. The genus name therefore refers to the planet Mars, alluding to the strange characteristics that seem to come out of nowhere, the species epithet is from Ancient Greek ηὕρηκα "I found it", echoing Archimedes' famous exclamation was meant to epitomize the troubles involved in the rediscovery of the species after the first specimen discovered in a soil sample was lost.