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The pharaoh ant Monomorium pharaonis

The pharaoh ant - Monomorium pharaonis - is a small yellow, almost transparent pest ant. It has been introduced almost into every area of the world and is particularly bothersome pest in hotels, grocery stores, hospitals or multifamily buildings. Being tropical species by origin, pharaoh ants also thrive in buildings of temperate regions with central heating present.

It is thought that Monomorium pharaonis came from West Africa somewhere at the beginning of XX century and was spread by the help of a man to Europe, Americas, Australasia and Southeast Asia. M. pharaonis is known as a “tramp” species, which means it is particularly reliant on human-mediated dispersal and has a close association with humans.

The workers of pharaoh ants are nearly the same size, around 1/13 inch (2 mm) long and are yellow or light brown with the tip of abdomen being little darker. The males are the same size as the workers but are black in color. The queens are 1/6inch (4 mm) in length and slightly darker than the workers. Antennae of pharaoh ants have 12 segments and this feature (together with the size) separates them from other quite similar species – thief ants, Solenopsis molesta which have only 10 segments.

Pharaoh ants are omnivorous, that is they feed on a wide variety of food. These ants are primarily nocturnal and prefer grease, meat and fat, but also feed on sugar, honey, cake, bread, butter and other products. Because of such taste they are a nuisance particularly in warehouses, grocery stores and other areas where food is kept and also pose a serious health treat in hospitals or clinics where they are attracted to medical preparations or even open wounds. Pharaoh ant presence in hospitals is of particular concern as they are vectors for the transmission of certain human bacterial pathogens, including Streptococcus pyogenes, Pseudomonas aeruginosa and Staphylococcus epidermidis, which commonly infect hospitalised patients.

Pharaoh ants choose nesting areas where the temperature is about 80°F and the humidity around 80% with proximity to food being of lesser importance as they forage quite long distances in search for food. Nests are found rarely outdoors but can be found almost anywhere indoors (including light sockets, potted plants, stored clothing and wall cracks or crevices).

It is hard to detect the nests of pharaoh ants because these ants live a quiet way of life. They do not exhibit territorial behavior and do not have nuptial flights. As colonies contain many queens, a part of older colony with several queens just moves away to establish a new one. Pharaoh ants breed throughout the year and it takes around 38-42 days to develop from egg to adult. A queen can lay up to 400 eggs in her lifetime and produces about 10 to 12 eggs per reproductive event. Queens can live a year or even more, while males last only around 3 weeks and workers reach about 9 or 10 weeks of age. A colony of pharaoh ants can have a population of several hundred thousand individuals.