Linepithema iniquum (Mayr 1870)
on Hymenoptera Name Server
Mesonotal dorsum with deep, step-like mesal impression; dorsum of head posterior of clypeus with > 5 erect setae; mesopleura and metapleural bulla lacking pubescence and strongly shining.
According to Wild (2007) L. iniquum exhibits considerable variation in size, color, propodeal form, pilosity, and pubescence. Characteristic for this species is the step-like impression in the dorsal outline of the mesosoma as e.g. this specimen on AntWeb. All specimens below key out to L. iniquum but there is quite some variation in the strength of the "step". The mesothorax at the constriction is always narrower (in lateral view) than the diameter of the fore coxa.
For L. iniquum in the Mata Atlântica Wild (2007) notes that: "Atlantic forest material from Brazil presents a more confusing array of variation, as specimens can be small to large, with scapes of varying length, pale yellow to black or bicolored, and sparsely to densely pubescent, with little apparent geographic pattern to the variation and occasional local sympatry of more than one form. A dark densely pubescent form, a yellow sparsely pubescent form, and intermediates have been recorded in sympatry at Nova Teutônia, Santa Catarina. A dark sparsely pubescent form, a yellow densely pubescent form, and a bicolored form are all recorded from Rio de Janeiro and São Paulo states, sometimes in local sympatry. Many specimens from Paraná state are bicolored."
At Cachoeira reserve I have collected a light brown, a dark brown and a bicolored form of L. iniquum. I have only few specimens available but these can be separated quite easily. I treat them all as L. iniquum at this time. One might speculate that more than one species is hidden under iniquum; at least in the population of the the Southern Mata Atlântica. Below, I present pictures and some notes on all forms to show the variation among individuals of this species.
L. iniquum is primarily an arboreal ant. My records are all from leaf-litter samples or baiting on the ground but this probalbly reflects occasional ground foraging. It has been recorded from sea level to over 2000m asl and ranges from Central America to Paraguay and Southeastern Brazil. I have collected this species in pastures, secondary forests and primary forests (though different forms in each habitat).