Pharaoh ants have become a serious nuisance pest in hospitals, rest homes, apartment dwellings, hotels, grocery stores, food establishments and other buildings. They feed on a wide variety of foods including jellies, honey, shortening, peanut butter, corn syrup, fruit juices, baked goods, soft drinks, greases, dead insects and even shoe polish. Also, these ants gnaw holes in silk, rayon and rubber goods. In hospitals, foraging ants have been found in surgical wounds, I.V. glucose solutions, sealed packs of sterile dressing, soft drinks, water in flower displays and water pitchers. These ants are capable of mechanically transmitting diseases and contaminating sterile materials. Some feel Staphylococcus and Psuedomonas infections, occurring from time to time in hospitals, are associated with these ants.

Identification

Pharaoh workers are very small (about 1/16-inch long), light yellow to reddish brown in color with the abdomen (hind portion of body) somewhat darker. There is no stinger. The petiole (narrow waist between the thorax and abdomen) has two nodes and the thorax has no spines. Eyes are well-developed. The antennal segments end in a distinct club with three progressively longer segments. This is in contrast to the thief ant's two-segmented club.

Life Cycle and Habits

Female Pharaoh ants can lay 400 or more 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 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. The entire life cycle takes about 38 to 45 days depending on temperature and relative humidity. Unlike most ants, they breed continuously throughout the year in heated buildings and mating occurs in the nest. A single queen can produce many hundreds of workers in a few months. Mature colonies contain several queens, winged males, sterile females or workers, eggs, larvae, prepupae and pupae growing to as large as 300,000 or more members.

Periodically a queen, together with a few workers carrying immatures (eggs, larvae and pupae), leaves the nest and sets up a new colony elsewhere, quickly spreading an infestation. This behavior pattern is known as "satelliting," "fractionating" or "budding" where part of the colony migrates to a new location rather than by single females dispersing after a reproductive swarm. Budding may occur due to overcrowding, seasonal changes in the building's central heating and cooling system or application of a repellent pesticide.

Nests are often so small it can be contained in a thimble, 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.

Control Measures

Pharaoh ants are usually much harder to control than other ants because of their ability to disperse. There may be dozens or hundreds of colonies in a single hospital and when a few colonies are missed during control, populations will quickly rebound. About 90 percent of the colony remains hidden in the nest so even if 10 percent of the colony is killed by a residual pesticide, the remaining reservoir of ants is enormous. Conventional contact pesticide applications especially repellent products such as pyrethrins may spread infestations to new areas with multiple colonies blossoming within the structure. These ants will avoid certain pesticides. Control is difficult and often long term (months to years), depending on the building size, wall voids, etc., especially in hospitals and food plants. Complete cooperation from the property manager and residents is essential for a successful control program.