Pharaoh ant

queen
Monomorium pharaonis, Queen surrounded by workers and eggs

Pharaoh ant (Monomorium pharaonis) is a very small species of ants. The worker ants reach a length of up to 3 mm, while the queens (the only fertile females in the colony) measure 5-6mm.

These insects live in polygynous societies, which means they contain a large number of fertile females called queens. These queens are sequentially reared from fertilized eggs in each healthy nest.

Males, known as drones, are only produced from unfertilized eggs when the colony needs them for division, budding, and mating with young queens. Mating occurs within the nest, and typical nuptial flights observed in most ant species do not take place.

Small, less populous colonies rear larger workers and queens. In these ant societies, the ratio of queens to workers varies between 1:3 and 1:12. A ratio of 1:3 is found in nests with approximately 300 workers, while a ratio of 1:12 is observed in nests with around 1500 individuals. The average colony consists of about 500-600 workers, larvae, eggs, pupae, and 50 queens.

Nests are typically established in warm habitats such as cracks in walls near heating systems or close to water sources, which the foragers actively bring to the nest, thereby increasing its humidity.

The workers of this species are completely sterile, and the tasks assigned to them are determined by their age. Every healthy nest contains all developmental stages, including eggs, larvae, and pupae. Periodically, the population density becomes too high, leading to swarming, colony division, or budding.

larvae
Monomorium pharaonis, Workers feeding larvae

Budding involves transferring a portion of the colony members, including larvae and eggs (excluding queens), to a location previously recognized by the workers as suitable for nest establishment. This “bud,” isolated from the influence of queen pheromones, rears future young queens from the provided young larvae. Colony division, on the other hand, involves the migration of half or a portion of the population, along with the queens, to a future nesting site.

During laboratory studies, it was discovered that offspring colonies were much more likely to be formed in locations similar to the original colony’s location unless the quality of the new site was significantly higher. In such cases, the ants would choose the better location.

Queens of Monomorium pharaonis live for only a year and need to be successively replaced, just like workers, which have a maximum lifespan of 60-90 days. When colonies reach maturity, they search for suitable locations to establish new nests.

Newly formed ant families cooperate and share food with others, creating a network of interconnected cities through ant trails.

At a temperature of 27°C, the entire developmental period from egg to adult (mature ant) lasts from 39 to 45 days. For queens, it takes 11 days for eggs, 22 days for larvae, and 12 days as pupae, totaling 45 days. For workers, it takes 11 days for eggs, 18 days for larvae, and 10 days as pupae, totaling 39 days. Development is halted at temperatures below 18°C, which is lethal to the ants. If it persists for too long, it leads to the extinction of workers due to the lack of generational replacement. The sum of degree-days for worker development is 351, while for queens, it is 405. Under ideal conditions, which are surprisingly difficult to achieve, the doubling time of the colony is approximately 70 days.

It is important to note that above 30°C, despite a shortened development period, there is a continuous increase in mortality among eggs and larvae. Above 40°C, mortality is high enough to cause colony death. The optimal temperature for development falls within the range of 27-28°C. Any decrease or increase in temperature increases mortality and limits colony productivity.

Monomorium pharaonis is an omnivorous ant, but for optimal colony growth, it requires animal proteins for rearing a large number of larvae and carbohydrates for adult ants. The best protein-to-carbohydrate ratio (P:C) ranges from 1:2 to 1:4, and the ants actively regulate this ratio by choosing suitable food sources.

Workers continuously transport water to the colony, increasing humidity levels and enabling survival in dry environments, as these ants originate from desert and semi-desert regions.

The species has a global distribution, with Monomorium pharaonis already occurring naturally in tropical and subtropical regions. In temperate climate areas, their presence is closely associated with human habitats and heated indoor spaces.

Although almost blind, these insects have retained their ability to perceive light. Their initial response to disturbance is to seek dark places for hiding, but over time, most colonies adapt to normal, non-overheating light conditions and carry out their tasks in a regular manner, allowing for easy observation of the superorganism behaviors they create.

Their ability to navigate their surroundings relies on a highly sensitive sense of smell. Ants lay down pheromone trails on the ground, which they follow. Some of these trails resemble highways, connecting individual ant cities or leading to water and food sources. Some trails are transient, while others persist for a long time.

On the right – video showing the Monomorium pharaonis life cycle.

See the similarity with honeybees – the genus Apis and other social insects.