The pharaoh ant, monomorium pharaonis (linnaeus), is a species that is considered to be a serious pest in many parts of the world. Carolus Linnaeus (1707 - 1778), the Swedish botanist and taxonomist, thought that this species of ant originated in Egypt. He mistakenly believed that this small, yellow ant was one of the plagues in the time of the pharaohs and having come to this conclusion on very little evidence, he named them pharaoh ants. In fact they are thought to have evolved from wasps in North or Tropical Africa and no link with Egypt has ever been proven.
They have since established a worldwide population, having been spread as an unintentional result of the commercial activity of humans, and are now a particularly common pest in the USA and Japan. They cannot survive extreme cold but they have adapted to living indoors alongside human beings.
Pharaoh ants are very small (2mm long) and yellow to reddish brown; but queens are longer (4mm), darker and sometimes have wings. Like all insects they have three segments to their bodies (head, thorax, and abdomen) and six legs. Their antennae have 11 or 12 segments, ending in clubs with three segments, and this distinguishes them from thief ants, which they closely resemble1. The antennae of the males are not elbowed.
Pharaoh ants are commonly found in kitchens and storerooms. They like places that are warm and humid. They will nest in any crack or crevice in any structure such as between bricks and also folded bags or newspapers. Pharaoh ants will also nest in and around appliances such as refrigerators or stoves that have food or water around them. In subtropical areas, they will nest outside in leaf litter, piles of bricks, potted plants, under roof shingles, and in debris on flat roofs.
Colonies of pharaoh ants can become very large. They often contain as many as 300,000 workers with several hundred queens. There is no swarming and new colonies are formed by budding2. In warm climates, where the ants can survive outdoors, they will move from building to building. New nests can be formed with as few as five workers, ten pre-adults, and one queen.
Pharaoh ants are omnivorous. They feed on a variety of foods including fats, proteins and carbohydrates (particularly sugars), and will also take and kill small insects. They use carbohydrates primarily for maintenance; protein is required for larval development and egg production by the queens. They need moisture and, in modern houses with very dry interiors, they may sometimes be seen drinking from the water taps. The workers forage some distance from the nest, and establish pheromone3 trails to food and water sources. Once a worker ant locates a food source during a foraging expedition, it lays a chemical trail from the food to the nest. When workers return to the nest, they excite other workers to follow the trail to the food source. The chemical trails are often many metres long. Workers sometimes use electrical and telephone wires as routes to travel through walls and between floors.
Love and War
Mating takes place inside the nest. The development of eggs into adult takes about 38 days, provided that the temperature is warm. Workers live about nine or ten weeks, with only ten percent going out to feed at one time; queens live much longer (from four to 12 months); and males die about three to five weeks after mating. Nests spread by budding when food supplies are threatened, thus interference with workers fetching food may well actually increase the number of ant colonies in an area.
Pharaoh ants are not warrior ants. Their stinger is present but not significant, and is used primarily to capture small prey insects rather than for defence. They do not cause noticeable stings to humans. Their principle form of defence against attack is the ability of the colony to bud, and it is this ability that makes them such formidable pests.
Control of pharaoh ants is necessary because they spread diseases. They are a common problem in hotels, grocery stores, hospitals, and apartments. More than a dozen pathogenetic bacteria have been found on pharaoh ants collected in hospitals. Many of these bacteria are of medically important, opportunistic kinds including streptococcus pyogenes (which can cause can scarlet fever and rheumatic fever), and pseudomonas aeruginosa. Pharaoh ants will infest wounds, enter IV bottles while they are in use, and seek moisture from the mouths of sleeping infants.
Where pesticide controls are prohibited or unwelcome, physical barriers, such as sticky tape, petroleum jelly, or non-hardening glue are recommended to keep foraging workers away from sensitive areas.