Pharaoh ant workers are about one-sixteenth of an inch long, or 2mm in length. They are light yellow to reddish brown in colour with a darker abdomen (hind portion of body). There is a stinger. The petiole (narrow waist between the thorax and abdomen) has two nodes and the thorax has no spines. Eyes are poor and possess on average 32 ommatidia. The antennal segments end in a distinct club with three progressively longer segments.
Life Cycle and Habits
The pharaoh ant queen can lay hundreds of eggs in her lifetime. Most lay 10 to 12 eggs per batch in the early days of egg production and only four to seven eggs per batch later. At 27 °C (80 °F) and 80 percent relative humidity, eggs hatch in five to seven days. The larval period is 18 to 19 days, prepupal period three days and pupal period nine days. About four more days are required to produce sexual female and male forms. From egg to maturity takes about 38 to 45 days depending on temperature and relative humidity. They breed continuously throughout the year in heated buildings and mating occurs in the nest. Mature colonies contain several queens, winged males, workers, eggs, larvae, prepupae and pupae.
Pharaoh ants use pheromones as the primary means of communication. Part of the colony migrates to a new location. Nests can be very small, located between sheets of paper, in clothing or laundry, furniture, foods, etc. Nests usually occur in wall voids, under floors, behind baseboards, in trash containers, under stones, in cement or stone wall voids, in linens, light fixtures, etc. They prefer dark, warm areas near hot water pipes and heating tapes, in bathrooms, kitchens, intensive care units, operating rooms, etc. They are “trail-making” ants and often are found foraging in drains, toilets, washbasins, bedpans and other unsanitary sites as well as in sealed packs of sterile dressing, intravenous drip systems, on surgical wounds, food and medical equipment.
In some areas, this ant has become a major pest of residences, food plants, factories, office buildings, apartments and hospitals. Infestations in hospitals have become a chronic problem in Europe and the United States where burn victims and newborns are subjected to increased risk because the pharaoh ant can transmit over a dozen pathogenic pathogens. Pharaoh ants have been observed seeking moisture from the mouths of sleeping infants and from in-use IV bottles.
Control of pharaoh ants is difficult, due to their nesting in inaccessible areas. Treatment must be thorough and complete at all nesting sites, as well as the foraging area. Thus, treatment must include walls, ceilings, floor voids, and electrical wall outlets. Baits are now the preferred method of control for pharaoh ants and several baits (insecticides) are labelled for indoor ant control. A pharaoh ant infestation of a multifamily building requires treatment of the entire building to control the infestation. Ants nesting on the outside may be controlled by also using a perimeter barrier treatment.
Baits cannot be placed in just any location and be expected to work. Pharaoh ant trails and their resources (both food and water) must be located for proper placement of baits and effective control. Non-repellent baits (such as boric acid, hydramethylon or sulfonamide) should be used, as repellent baits can worsen the situation by causing the colony to fracture and bud. As a result, ant activity will briefly diminish as the new colonies establish themselves, then again become a problem as the foragers resume activity in a new location. It is recommended not to exterminate using sprays and dusts because they will cause the pharaoh ants to scatter.