MMPC Field Guide: Ants

Ants are social insects in the family Formicidae, instantly recognizable by their slender “wasp-waist” body and elbowed antennae.

Of the 792 ant species documented in the U.S., only about 50 consistently invade structures. Outside, they’re ecosystem architects—tunneling soil, dispersing seeds and preying on other pests. Indoors, they’re opportunists: sugar-craving pavement ants scour kitchens, while carpenter ants exploit damp wood in wall voids and subfloors.

Biology

Colonies house one or more egg-laying queens and thousands of sterile female workers. Many species bud off sub-colonies under stress (notably pharaoh and odorous house ants), creating sprawling supercolonies without ever flying. Others (pavement, carpenter ants) rely on mass swarms in late spring or early summer, after which fertilized queens shed wings and establish fresh nests.

Foraging follows pheromone highways: scouts blaze the trail to a spill, nestmates reinforce it into bustling traffic. In spring and early summer, workers target proteins and fats to fuel brood development; later they switch to carbohydrate-rich sweets for adult energy. Because adult ants can only ingest liquids, solid food is carried back to larvae, liquefied by digestive enzymes, then shared mouth-to-mouth (trophallaxis) throughout the colony.

On warm, humid days—often after rain—mature colonies flood the air with winged males and females. After a mid-air mating flight, queens drop their wings and burrow to launch new colonies that, in some carpenter species, take 3–6 years to amass thousands of workers.

Risks

Ant infestations pose several threats. Carpenter ants hollow out damp or decayed wood to build galleries, discarding clean, coarse‐sawdust frass and weakening structural beams over time.

Sugar‐ and grease‐seeking species such as pavement, odorous house and pharaoh ants infiltrate pantries and food‐prep areas, spoiling products and potentially spreading pathogens—pharaoh ants have even been documented traversing IV lines in hospitals in search of moisture.

Although bites from common household ants are uncommon, species that inject formic acid can cause sharp pain or a burning sensation; most encounters result in only transient welts, but individual sensitivity varies and rare allergic responses can occur.

Identification

Most household ants wear drab browns, blacks or reds but sport the same three-part, six-legged build with strong mandibles and geniculate (elbowed) antennae.

Their bodies split into three segments—head, mesosoma (thorax + propodeum) and gaster—linked by a narrow petiole that may bear either one or two bead-like nodes, a key ID feature in the field.

Worker sizes run the gamut from diminutive pharaoh and ghost ants at roughly 1.5 mm (1/16″) up to hefty carpenter ants reaching 13 mm (1/2″).

Odorous House Ant

Tapinoma sessile

Odorous house ants are tiny—workers clock in at just 2.4–3.3 mm (1/16″–1/8″) and remain uniform in size (monomorphic). Their single petiole node hides beneath the gaster, and the uneven thoracic profile gives the side view a slight dip.

When crushed or disturbed, they release a rotten-coconut odor, a trademark field cue. Colonies form supercolonies with multiple queens and interconnected nests in both outdoor and indoor harborage, wherever moisture and heat persist.