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Color & shape are wrong for Formica exsectoides. This is another Formica in the rufa species group, not sure which one.
This is not the army ants' larva, but a captured pupa of another ant species in the genus Camponotus. Army ants eat the brood of other species, so immature ants captured in the columns are not necessarily those of the army ants.
Brown & black Odontomachus are probably different species. This red one is likely related to true O. brunneus but may actually be undescribed. The black one might be O. haematodus or O. bauri, both are common in Brazil.