"The Pharaoh Ants" (Monomorium pharaonis)

The pharaoh ant is distributed worldwide and is established throughout the United States and Canada. It is believed to have come to the United States from Europe and may have originated in the Old World tropics. Riley (1889) is of the opinion it received the "scientific name of 'Pharaoh ant' on account of a defective knowledge of Scripture on the part of its describer, who doubtless imagined that ants formed one of the plagues of Egypt in the time of Pharaoh, whereas the only entomological plagues mentioned were lice, fleas and locusts."

Outside the tropics, M. pharaonis is dependent on artificial heating and is invariably associated with human habitation. Infestations commonly occur where food is stored or handled (i.e. apartment buildings, bakeries, health care facilities, homes, office buildings, pet shops, restaurants and zoos).

Riley (1889) found this ant is not a nuisance "from the actual loss which it causes by consuming food products, but from its inordinate faculty of getting into things." This ant has been observed feeding on such sweets as sugar syrups, fruit juices, jellies, cakes and fruit pies, as well as greases, shoe polish, bath sponges, insect collections and on the juices of recently deceased cockroaches. Lintner observed them running all over the dining table and getting in the food, and he made the interesting note that "a large number of these insects in food can impart an agreeable acid flavor." Although this ant feeds on sweets, it is believed by some to prefer fatty foods. It is known to be predacious on a wide variety of insects among which are bed bugs, crickets, white grubs and cotton boll weevils. Martini (1934) saw ants of the same genus attack children in a hospital. Ploschke (1943) found these ants to be serious pests on a hospital ship, where the ants frequently entered the wounds, and were suspected of transmitting germs by contact.

Beatson (1972) reported more than a dozen pathogenic bacteria found on Pharaoh ants collected from hospitals. These included Streptococcus pyogenes, Pseudomonas aeruginosa and Staphylococcus epidermidis. Keith Story (personal communication) reported particular problems of Pharaoh ant infestations in operating theaters and intensive care units where pest control measures often are discouraged by medical staff who are unaware of the disease transmitting potential of these ants. Story further reported pharaoh ants have penetrated the security of recombinant DNA laboratories. Rachesky (1974) incriminated this pest with the death of baby reptiles in a zoo. Granovsky and Howell (1983) reported this ant infested around 25 percent of 57 randomly selected hospitals throughout Texas. Granovsky indicates there are more than 20 types of bacteria which have been isolated from Pharaoh ants, many of which are medically important, opportunistic bacteria.

In domestic situations, nest of Pharaoh ants are unstructured, i.e. this ant tends to occupy nearly any crack or crevice which has suitable microclimate, rather than the physical construction of a nest with tunnels and chambers. In infested buildings, ants are often most numerous around areas where high temperature and humidity prevail (i.e. air conditioning units, boiler houses, heating ducts, kitchens, laundries and window ledges). Outside these areas, the ants are most often found near heating pipes and radiators, sinks, drains and toilets. New nests often remain in contact with their parent colony within the same structure. Thus brood, workers and food can be shared between several nests (polydomic). The nests were observed by Riley to occur "in almost any secluded spot, between the walls or under the floors or behind the baseboards, or among trash in some old box or trunk, or in lawn or garden walk just outside the door." Zappe (1917) observed their apparent affinity for the bathroom or kitchen, where they were seen drinking water. Since these ants may nest in relatively dry situations in the house, the popularity of the kitchen and bathroom faucets may be accounted for by their need for moisture, especially for rearing their young.

Peacock et al. (1959) have published the results of an extensive study on the life history and control of this ant. Under laboratory conditions of approximately 80 degrees F and a relative humidity of 80 percent, the life history of the Pharaoh ant worker is approximately as follows:

Regarding females and males, there is evidence that the life history period is about four days more, presumably because their larger size as larvae necessitates a longer period of feeding and growth.

Pharaoh ants are omnivorous. They feed on a wide variety of foods including fats, proteins and carbohydrates and will also take and kill small insects. Once a foraging worker locates a food source, it lays a chemical trail from the food to the nest. Returning workers enter the nest and "excite" other workers to follow the trail to the food source. These chemical trails are often many meters long.