Cornfield Ant

Small (2.5–3 mm), light brown, single petiole node, 12-segmented antenna. Mounds are loose piles of fine soil pushed up between pavers, around fence posts, and along sidewalk edges, especially after summer rain. Easily confused with other small brown lawn ants, confirm with hand lens.

Polygyne or monogyne depending on population; large interconnected colonies under turf. Famous for an obligate mutualism with the corn root aphid (Anuraphis maidiradicis), workers carry aphid eggs into the nest, store them through winter, and place hatchlings on corn roots in spring, a remarkable behavior with real economic cost in corn.

Cosmetic in lawns and athletic fields, mounds damage mower reels and ruin putting greens. Real economic pest in corn through root aphid farming. Rarely enters homes.

Granular turf insecticides applied broadcast in late spring control both ants and aphid mutualism. In agricultural fields, neonicotinoid seed treatments (clothianidin, thiamethoxam) on corn provide indirect control by killing the root aphids the ants tend.

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