A stable source of carbohydrates is essential for the longevity of ant colonies. Foraging ants must select among carbohydrate resources, such as aphid honeydew, that vary based on sugar type, volume and concentration. Using Western carpenter ants, Camponotus modoc, and European fire ants, Myrmica rubra as model species, we tested the hypothesis that ant foraging on aphid honeydew is driven by aphid-specific sugars (unique sugars biosynthesized by aphids) and that ants will selectively consume particular mono,- di-, and tri-saccharides. In choice bioassays, we offered whole ant colonies with aqueous sugar solutions and measured their consumption. In C. modoc, common sugar constituents (rather than aphid-specific sugars) and sugar concentration affected consumption by ants. Colonies of C. modoc and M. rubra preferred fructose to other monosaccharides (xylose, glucose) and sucrose to other disaccharides (maltose, melibiose, trehalose). Conversely, when offered a choice between the aphid-specific trisaccharides raffinose and melezitose, C. modoc and M. rubra favored raffinose and melezitose, respectively.