The Argentine ant, Linepithema humile, is an invasive species of significant ecological and economic concern known for creating enormous supercolonies across the globe. Originating in South America, these small, highly adaptable insects have spread worldwide, often thriving in urban and suburban environments. The primary question for most people encountering this prolific pest is whether they bite or sting.
The Direct Answer: Biting vs. Chemical Defense
Argentine ants do not possess a functional stinger and are not considered to bite humans in a painful or medically significant manner, unlike species such as fire ants. Worker ants may attempt to pinch the skin with their small mandibles if threatened, but this action is usually too weak to be felt or to break the skin. Their primary defense mechanism is chemical rather than physical.
Instead of injecting venom, they spray a defensive compound known as formic acid from an opening at the tip of their abdomen called an acidopore. Formic acid, a corrosive substance also found in stinging nettles, can cause a mild, temporary burning or irritating sensation if sprayed onto a small wound or sensitive skin. For a human, the reaction is negligible and requires no medical treatment.
Identifying Argentine Ants
Worker ants are uniformly small, measuring about one-sixteenth to one-eighth of an inch in length, with a light to dark brown coloration. A distinguishing physical feature is their single-node waist, or pedicel, which connects the thorax and abdomen.
Beyond physical appearance, their behavior provides the most reliable field identification. They are notorious for forming massive, multi-lane trails, sometimes three or more ants wide, moving continuously between their multiple nest sites and a food source.
Furthermore, when an Argentine ant is crushed, it emits a specific, stale or musty odor, a characteristic that differentiates it from other species. This musty scent is crucial for identification because the similar-looking Odorous House Ant produces a distinctly different smell, often compared to rotten coconut, when disturbed.
Why Argentine Ants Are Considered Pests
Even though they do not pose a direct physical threat, the Argentine ant is classified as a major pest due to its unique social structure and massive population size. They form vast supercolonies, which are extensive networks of interconnected nests containing hundreds of queens and millions of workers that cooperate across large geographic areas. This lack of aggression between neighboring nests allows them to rapidly displace native ant species, fundamentally disrupting local ecosystems.
This invasive behavior extends into gardens and homes where they contaminate food, particularly sources of sugar, and can spread bacteria as they forage across surfaces. They also engage in a symbiotic relationship with plant pests, such as aphids and scale insects, protecting them from predators.
The ants actively “farm” these insects to harvest the sugary waste product they excrete, known as honeydew, thereby exacerbating existing issues with plant health and agricultural damage. Their tendency to enter structures in huge numbers, especially during periods of wet or dry weather, makes them a persistent and difficult nuisance to manage.
Addressing Infestations
Managing an Argentine ant infestation requires a strategic approach. The first line of defense involves exclusion and sanitation, focusing on eliminating access points and removing food and moisture sources. Sealing structural cracks, trimming back vegetation that provides a bridge to the home, and promptly cleaning food spills are effective initial steps.
The supercolony structure means that conventional repellent sprays are largely ineffective and can even be counterproductive, causing the colony to split into smaller, separate groups, a process known as budding.
The most effective control method involves using slow-acting, non-repellent liquid baits. This bait allows foraging workers to consume the toxic material and carry it back to the hidden nests to share with the queens and larvae before the poison takes effect, ultimately targeting the entire colony population. For severe infestations, professional pest management intervention is often necessary.