The presence of ants can be undesirable in places meant to be sterile. They can also come in the way of humans by their habit of raiding stored food, damaging indoor structures, causing damage to agricultural crops either directly or by aiding sucking pests or because of their stings and bites.

Soil and Ground-Nesting Ants

Argentine Ant

The Argentine ant, Linepithema humile (formerly Iridomyrmex humilis), is a dark ant native to northern Argentina, Uruguay, Paraguay, and southern Brazil. It is an invasive species that has been established in many Mediterranean climate areas, inadvertently introduced by humans to many places, including South Africa, New Zealand, Japan, Easter Island, Australia, Hawaii, Europe, and the United States.

Argentine ants are a common household pest, often entering structures in search of food or water (particularly during dry or hot weather), or to escape flooded nests during periods of heavy rainfall. When they invade a kitchen, it is not uncommon to see two or three queens foraging along with the workers. Eliminating a single queen does not stop the colony's ability to breed.

Crazy Ant

The crazy ant is an agricultural and household pest in most tropical and subtropical areas, and is a pervasive indoor pest in temperate areas. It has the ability to successfully survive in highly disturbed and artificial areas, including ships at sea and it can live indoors with humans.

In the United States, the crazy ant has widespread population from Florida to South Carolina and west to Texas. It commonly is found in residences and warehouses over much of the eastern United States and in California and Arizona. Populations are also reported from Hawaii, Missouri and Virginia, as well as Buffalo (New York) and Boston (Massachusetts).

The crazy ant worker is relatively small (2.3-3 mm). The head, thorax, petiole, and gaster are dark brown to blackish; the body often has faint bluish iridescence. The body has long, coarse, well scattered, suberect to erect, grayish or whitish setae. The antennae of the crazy ant have 12-segments without a club and are extremely long. The scape, the basal segment of the antenna, is extraordinarily long with the apex surpassing the posterior border of the head by at least one-half the scape length. Eyes are elliptical, strongly convex, and placed close to the posterior border of the head.

Odorous House Ant

When killed by crushing, these ants give off an unpleasant order, hence the name. They are one of the more common household invaders. They are brown to dark brown in color and about 1/10 of an inch long. Odorous ants prefer sweets as their food source, as well as insects and the honeydew insects produce.

Odorous ants nest in the soil, typically near or under objects laying on the ground such as rocks, boards, firewood, the base of patios or mulching plastic. They might also nest inside the home in wall voids or under the floor. Their mating season is during June and July.

Bigheaded Ant

Pheidole megacephala is a species of ant in the family Formicidae. It is commonly known as the bigheaded ant in the USA and the coastal brown ant in Australia. It is a very successful invasive species and is considered a danger to native ants in Australia and other places. It has been nominated as one of the hundred "World's Worst" invaders.

There are two types of worker ants, the major or soldier ant and the minor worker. The common name of bigheaded ant derives from the soldier's disproportionately large head. This has large mandibles which may be used to crush seeds. The soldiers are about four millimetres in length, twice as long as the minor workers. The colour of both types varies from yellowish-brown or reddish-brown to nearly black. The rear half of the head is smooth and glossy and the front half sculptured. The twelve-segmented antennae are curved and have club-like tips. The waist or petiole is two-segmented with the node immediately behind conspicuously swollen. There are a pair of short, upward-facing spines on the waist. The body has sparse, long hairs.

Red Imported Fire Ant

The red imported fire ant (Solenopsis invicta), or simply RIFA, is one of over 280 species in the widespread genus Solenopsis. Although the red imported fire ant is native to South America, it has become a pest in the southern United States, and many other countries. RIFA are known to have a painful, persistently irritating sting that often leaves a pustule on the skin.

The Red Imported Fire Ant is a very aggressive eusocial species. They are far more aggressive than most ant species, and have a painful sting. Animals, including humans, often encounter them by inadvertently stepping on one of their mounds, which causes the ants to swarm up the legs, attacking en masse. The ants respond to pheromones released by the first ant that attacks, thereafter stinging in concert.

Arial and Ground-Nesting Ants

Whitefooted Ant

Technomyrmex albipes (White footed ant) is a species of ant first described from Indonesia in 1861, the white footed ant neither bites nor causes structural damage. Yet it is considered a nuisance due to their explosive population growth.

Although not native to North America, the insects were accidentally imported into Florida where they were first collected and identified in 1986. New information from Bolton indicates that the white-footed ant in Florida is Technomyrmex difficilis.

Ghost Ant

Tapinoma melanocephalum is a species of ant that goes by the common name ghost ant. They are recognized by their dark head and pale or translucent legs and gaster (abdomen). This coloring makes this tiny ant (1⁄16 of an inch) seem even smaller.

The ghost ant's diet consists mainly of sweets but they will also feed on grease and occasionally living or dead insects. They exhibit a high need for moisture, and although colonies are usually established outside, they can readily "set up camp" inside domestic houses during dry conditions.

This is a widespread tropical species, found throughout the world. Its native range is unknown. The ghost ant is thought to be so named because the legs and abdomen of the insect look transparent, with only the head and thorax being dark brown in colour. Observed in infested buildings with the naked eye they are quite difficult to distinguish from pharaoh ants, being virtually of the same size.

Black Carpenter Ant

The black carpenter ant (Camponotus pennsylvanicus) is a species of carpenter ant. It is the most common carpenter ant pest in the United States.

Black carpenter ants are known to forage up to 100 yards in search of food. Workers are most active at night, traveling from their nest to a food source following trails. They do establish chemical (pheromone) trails. The ants produce crackling sounds that can often be heard near a large nest. A large colony can have thousands of individuals. The black carpenter ant does not sting, but the larger workers can administer a sharp bite, which can become further irritated by the injection of formic acid, which they produce. Black carpenter ants are fiercely territorial with regard to other ants. Black carpenter ants do not eat or digest wood, but they tunnel through wood, which can cause structural damage.

Florida Carpenter Ant

The Florida carpenter ant complex is comprised of several species, two of which are common around structures: Camponotus floridanus (Buckley) and Camponotus tortuganus (Emery). These bicolored arboreal ants are among the largest ants found in Florida, making them apparent as they forage or fly indoors and out.

During the flight season, carpenter ants can often be found in alarming numbers. Sometimes homeowners are concerned about damage to the structural integrity of their homes, which they sometimes incorrectly learn, is caused by Florida carpenter ants. However, unlike the wood-damaging black carpenter ant, found in Florida's panhandle and a few other western U.S. species, Florida carpenter ants seek either existing voids in which to nest or excavate only soft materials such as rotten or pithy wood and Styrofoam.

Interior-Nesting Ants

Theif Ant

Thief ants tend to be the most common household invader of the ant kind. They are called thief ants because they often nest near other ant colonies and steal their larvae for food. They resemble Pharaoh ants (see below) in appearance, so you may need a pest control specialist to identify them correctly. Generally, however, they are yellow to light brown in color and the worker ants are approximately 1/20 of an inch long. Another distinct characteristic is their tendency to curl up when dead. Their mating season is July through September.

Pharaoh Ant

The Pharaoh Ant (Monomorium pharaonis) is a small yellow or light brown, almost transparent ant notorious for being a major indoor nuisance pest, especially in hospitals. The pharaoh ant, whose origins are widely unknown, has now been introduced to virtually every area of the world, including Europe, the Americas, Australasia and Southeast Asia. This species is polygynous, meaning each colony contains many queens, leading to unique caste interactions and colony dynamics. This also allows the colony to fragment into bud colonies quickly. Colonies do not display aggression toward each other; this is known as unicoloniality. Monomorium pharaonis is also notable for its complex foraging system, involving intricate trail routes maintained with several pheromones. It was the first ant species discovered to use a negative (repellant) pheromone. These chemicals are integral for communication in this species. Pharaoh ants are a tropical species, but they thrive in buildings almost anywhere, even in temperate regions provided central heating is present.