The Pharaoh ant is omnivorous and their broad diet is reflective of their tolerance of diferent habitats. Pharaoh ants feed on sweets: jelly, sugar, honey, cakes, and breads. They also enjoy greasy or fatty foods such as pies, butter, liver, and bacon. Believe it or not, a preference of freshly used medical bandages attracts these ants to hospitals. These ants may find also their way into your shoe polish. In their natural environment, Pharaoh ants may be found enjoying a recently deceased insect such as a cockroach or a cricket. Pharoah ants use chemical trails laid down by other workers in order to find food.
Animal Foods: eggs; body fluids; carrion ; insects; terrestrial non-insect arthropods
Plant Foods: seeds, grains, and nuts; fruit; nectar; sap or other plant fluids
Other Foods: fungus; detritus
Foraging Behavior: stores or caches food
Primary Diet: omnivore
5 to 6 days after being laid, Monomorium pharaonis eggs hatch into larvae. Larvae grow and develop over 22 to 24 days, passing through several instars “growth phases which end with molting). When the larvae are ready, they enter the pupal stage to undergo complete metamorphosis that is complete 9 to 12 days later. The pupal stage is the most vulnerable to environment and predators. The pupae are relatively inactive, and do not eat. Therefore, adult ants take a total of 38-45 days to fully mature, while another 4-5 days are required for sexual forms to reach maturity.
As the larvae grow, they must molt to a larger stage or instar. Molting is regulated by the molting hormone, ecdysone. This hormone is released by a gland located in the thorax, which is stimulated by the "brain hormone" produced by neurosecretory cells. Another hormone called juvenile hormone is most abundant in immature stages of the ant, and decreases with the passing of each stage toward adulthood.
Development - Life Cycle: metamorphosis
There is no special status for this ant.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Pharaoh ants communicate through tough and chemical markers called pheremones. They are have very good eye sight and can sense vibrations of potential predators or movement from their own larvae.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: pheromones ; scent marks ; vibrations
Perception Channels: tactile ; chemical
The Pharoah ant may be confused wtih the Thief ant. This ant is similar in physical characteristics, except has a more yellow tint to its body. Also, the foods eaten by this ant are similar to those of the Pharoah ant. College campuses are excellent breeding grounds for the Pharoah ant, especially the kitchen or dormitories. (Klots and Klots 1959)
Because of their attraction to soiled bandages, hospitals must limit patient exposure to this pest. The microscopic bacteria that these ants can carry is sometimes pathogenic, including Salmonella, Pseudomonas, Clostridium, and Staphylococcus. Also Pharaoh ants can annoy home owners by congregating on food and dishes left unattended.
Negative Impacts: injures humans (causes disease in humans ); household pest
Monomorium pharaonis removes and feeds upon crumbs and bits of food left unattended. Living with humans, these insects do not swarm as other ants, and they limit other household pests such as cockroaches by eating the leftover, exposed food supply.
Positive Impacts: controls pest population
Little is known on the effects these ants have on their native environment. In areas where they have been introduced they are considered to be a household pest.
The Pharaoh ant is limited by cool climates, and relies upon humans for a suitable home in northern regions. This ant originates in the Old World tropics of Africa and has migrated to areas acrss the globe.
Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); oriental (Introduced ); ethiopian (Native ); neotropical (Introduced ); australian (Introduced )
The diversity of habitats the Pharaoh ant can live in is amazing! In Northern climates however, their nests often occur within households--the spaces in walls between the studs and insulation offer warm breeding grounds relatively hidden from our [human] eye (Howard, 1908). A major nuisance in the United States, the Pharoah ant is small, and difficult to gauge in population size. Their colonies are ruined by sealing cracks, and cutting off exposure to food. Kerosene has historically been used for this purpose (Klots and Klots 1959).
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Other Habitat Features: urban ; suburban ; agricultural
Definitely one of the smallest ants at a mere 1/12 or 1/16 of an inch, their bodies are reddish brown to slightly tan in nature (Drees and Jackman 1998). Each compound eye has 20 facets, and each mandible has four teeth. Paired longitudinal and metanotal grooves are definitely distinct. The prodpodeal dorsum has no "standing hairs" (Ogata, et al 1998).
Pharoah ants (like all insects) have three main body sections: thorax, head, and abdomen, and three pairs of jointed legs that are attached to the thorax. Pharaoh ants use their antennae to sense vibrations, and for aiding vision in non-lighted areas. Small hairs that may be present on the abdomen can aid in sensing the weather, or by processing touch. Finally, like all arthropods, they contain a hard exoskeleton and additionally have a waxy cuticle to prevent drying out. Arthorpod skeletons are made of chitin, a polymer derivative of starch similar to our fingernails (Raven and Johnson 1999).
Range length: 1 to 2 mm.
Sexual Dimorphism: female larger
Other Physical Features: ectothermic ; bilateral symmetry
Since these ants are so small, little is known about the predators of this species.
Pharaoh ants have copulatory organs for internal fertilzation. After the new queen has mated with at least one male (sometimes more) she will store the sperm in her spermatheca so that she can use it to fertilize all of her eggs throughout the rest of her life.
Like most ants, sexual castes (those capable of reproduction) copulate in a “nuptial flight”. This is when environmental conditions are favorable to encourage mating and males and virgin queens fly into the air at the same time in order to find mates. After a short while the males die, and the queens lose their wings and find a place to begin her colony.
Mating System: eusocial
After a queen mates, she will found a new colony. This means that she will lay eggs and care for the first brood herself. After the first generation mature, they will care for the queen and all future generations as the colony grows. In addition to the founding of a new colony by a newly mated queen, colonies may also “bud”. This is where part of an existing colony carries brood to another "new" nesting site along with a new queen --often a daughter of the parent colony’s queen.
Key Reproductive Features: iteroparous ; year-round breeding ; sexual ; fertilization (Internal ); sperm-storing ; delayed fertilization
After a queen mates, she will found a new colony. This means that she will lay eggs and care for the first brood herself. After the first generation mature, the new workers will care for the queen and all future generations as the colony grows.
Taxonomic history
Mayr, 1865 PDF: 90 (m.); André, 1883a: 338 (q.); Forel, 1891c PDF: 164 (w.q.m.); Wheeler & Wheeler, 1955c PDF: 121 (l.); Petralia & Vinson, 1980 PDF: 383 (l.); Imai, 1966b PDF: 119 (k.).Combination in Monomorium: Mayr, 1862 PDF: 752.Senior synonym of Monomorium antiguensis: Roger, 1862c PDF: 294.Senior synonym of Monomorium domestica: Roger, 1862c PDF: 294.Senior synonym of Monomorium fragilis: Mayr, 1886c PDF: 359.Senior synonym of Monomorium contigua: Mayr, 1886c PDF: 359.Senior synonym of Monomorium minuta: Emery, 1892c PDF: 165; Bolton, 1987 PDF: 288.Senior synonym of Monomorium vastator: Donisthorpe, 1932c PDF: 449.See also: Smith, 1979: 1383; Bolton, 1987 PDF: 356; Atanassov & Dlussky, 1992: 164; Heterick, 2006 PDF: 100.Cosmopolite grace a son introduction dans les maisons (commun a Paris notamment). Cite de toute l'Afrique occidentale, meme en foret. Pris abondamment au Camp IV (foret, l.000 m.), et dans les mousses de foret primaire nord-est par VILLIERS. Etant donne que LamOTTE ne l'a trouve ni pres des villages ni en savane, que de plus le groupe Pharaophanes est essentiellement ethiopien, il y a lieu de croire que le banal M. pharaonis est originaire des forets africaines occidentales, et non d'Egypte ou des Indes comme l'ont suggere divers auteurs.
Diese Ameisenart ist jedenfalls die bedauernswuerdigste ihres Gleichen, denn nicht nur, dass sie durch Pflanzen oder Waaren in die ganze Welt zerstreut wurde, haben, sie auch die Naturforscher von einer Gattung zur andern geworfen, und ihr auch die verschiedensten Artnamen beigelegt. Ich glaube, dass nun ein Ruhepunct fuer dieselbe eingetreten ist, denn Herr Dr. Roger ist in Beziehung des Artnamens gluecklich bis zu Linne zurueckgegangen, indem er Formica Pharaonis L., F. antiguensis F., Myrmicadomestica Shuck, und M. (Diplorhoptum) molesta Smith (nicht Say) als synonym erklaerte. In generischer Beziehung trug derselbe bereits die Namen Formica , Myrmica , Diplorhoptrum und Pheidole . Smith stellte sie zu Diplorhoptum, o bschon er selbst in der Characteristik seiner sechsten Subdivision der Gattung Myrmica ( Diplorhoptrum ) angibt, dass die [[ worker ]] und [[ queen ]] zehngliedrige Fuehler (obschon auch gefehlt, denn das [[ queen ]] dieser Gattung hat eilfgliedrige Fuehler) und eine zweigliedrige Keule haben, waehrend unsere Art zwoelfgliedrige Fuehler und eine dreigliedrige Keule hat. Dass Smith wirklich dieselbe Art vor sich hatte, erhellt daraus, dass er mir schon vor der Herausgabe seines Catalogue Exemplare sandte, welche wirklich zu dieser Art gehoeren. Herr Dr. Roger stellte sie in seinen „ Beitraegen zur Kenntniss der Ameisen der Mittelmeerlaender " zur Gattung Pheidole , ohne Gruende anzufuehren, ueberdiess legt er derselben eilfgliedrige Fuehler bei, obschon er die echte Art hatte, wie ein Exemplar beweist, welches ich von ihm erhalten habe. Im heurigen Jahre stellte er sie in der Berliner entomologischen Zeitschrift zur Gattung Myrmica . - Ich erlaube mir nur, die Bitte an die oben genannten Herren Myrmecologen zu stellen, einen [[ worker ]], ein [[ queen ]] oder ein [[ male ]] dieser Art nach den analytischen Tabellen in meinen Europ. Formic, zu bestimmen und jedermann wird mit der groessten Leichtigkeit zur Gattung Monomorium gelangen, mit welcher diese Art in jeder Beziehung uebereinstimmt; zur weiteren Ueberzeugung kann man noch den Gattungscharacter von Monomorium pag. 71 lesen und wird dann nicht mehr den geringsten Zweifel haben. Die Beschreihung des [[ queen ]] und [[ male ]] werde ich im Novarawerke folgen lassen.
Mir liegt diese Art vor aus Paris, London, Hamburg, Kasan, Manilla (in meiner Sammlung), Sidney, Chili (Novara) und dem Cap der guten Hoffnung (M. C. Vienn.).
Junk River in Liberia und Deutsch-Togo an der Sclavenkueste (Dr. Brauns).
Sansibar.
[[ queen ]] [[ worker ]] Surubres pres San Mateo. 250 metres, Fougeres, Costa Rica (P. Biolley). Espece cosmopolite.
[[ worker ]]. He Cerf, Providence. Espece cosmopolite, transportee par les vaisseaux.
Syst. Nat., ed. 12, I, 963.
Massaua (Beccari); molti esemplari [[ worker ]] [[ queen ]].
Specie cosmopolita.
Canindeyú , Central, Concepción (ALWC, IFML, INBP). Literature records: Central, Concepción (Fowler 1981). [* = species not native to Paraguay]
Monomorium pharaonis,M. salomonis and M. subopacum are the only species in the Neotropics with head and mesosoma with fine reticulate-punctate sculpturation and mandibular dorsum with coarse longitudinal rugulae. M. pharaonis has two rows of hairs on the head between the vertex and carinae, which distinguishes this species from the other two. M. pharaonis is one of the best-known Old World tramp species.
Figs. 16, 91-92.
Formica pharaonis l. 1758:580. Syntype [[worker]]"s, Egypt [whereabouts of type material unknown]
Monomorium pharaonis (l.): Mayr 1862:752.
Formica antiguensis Fabricius 1793:357. Syntype [[worker]], West Indies: Antigua [whereabouts of type material unknown]. Syn. under M. pharaonis (l.): Roger 1862b: 294.
Myrmica domestica Shuckard 1838:627. Syntype [[worker]]"s,, Great Britain: London [no types known to exist]. Syn. under M pharaonis (l.): Roger 1862b:294.
Atta minuta Jerdon 1851:105. Syntype [[worker]]"s, India [no types known to exist]. Syn. under M. pharaonis (l.): Emery 1892:165.
Myrmica vastator Smith 1857:71. Syntype [[worker]]"s (lectotype here designated), Singapore (oxum) [examined].
Monomorium vastator (Smith) : Mayr 1886:359. Syn. under M destructor (Jerdon) : Dalla Torre 1893: 66. Syn. under M pharaonis (l.): Donisthorpe 1932:449.
Myrmica fragilis Smith 1858:124. Syntype [[worker]]"s (lectotype here designated), Singapore (bmnh) [examined]. Syn. under M. pharaonis (l.): Mayr 1886:359.
Myrmica contigua Smith 1858:125. Holotype, Sri lanka (BMNH) [examined]. Syn. under M pharaonis (L.) : Mayr 1886:359.
Material examined.- M. vastator : Lectotype: [[worker]], Singapore, J. Smith (OXUM). Four syntype workers are carded, two above and two below, on the one pin. The worker on the lower left-hand side (viewed from the rear of the pin) is here designated a lectotype to fix the name " vastator in the interests of stability. Monomorium pharaonis belongs to a small complex of closely related ants, and was also confused with Monomorium destructor by early researchers (Bolton 1987). Paralectotypes: Three workers, same data as the lectotype (OXUM). (The lectotype and three paralectotypes are covered with a uniform, thin layer of glue and cannot be separated.). M. fragile : Lectotype: [[worker]], Singapore, J. Smith (BMNH). Four syntype workers carded on one rectangle. The worker on the lower right (viewed from the rear) is here designated a lectotype to fix the name "fragile" in the interests of nomenclatural stability. Paralectotypes: Three workers, same data as the lectotype (BMNH). (The lectotype and three paralectotypes are glued and could not be separated without serious risk of damage.). M. contiguum : Holotype: [[queen]], Ceylon. J. Smith (BMNH).
Other material examined: Prov. Antsiranana: Res. Spec. Ankarana, 22.9 km 224 SW Anivorano Nord 10-16.ii.2001 Fisher et al. (1 [[worker]]); Sambava, 7.xi.1992 Solomon (1 [[queen]]) (MCZ). Prov. Fianarantsoa: Ranomafana NP, Talatakely 14.iv.1998 M.E. Irwin & E.I. Schlinger (4 [[worker]]). Prov. Mahajanga: P.N. Ankarafantsika, Ankoririka, 10.6 km 13 NE Tsaramandroso 9-14.iv.2001 Rabeson et al. (1 [[worker]]).
Worker description.- Head: Head oval; vertex weakly convex; frons shining and finely striolate and microreticulate; pilosity of frons consisting of a few short, thick, erect setae interspersed with short, appressed setulae. Eye moderate, eye width 1-1.5x greatest width of antennal scape; (in full-face view) eyes set above midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club three-segmented. Clypeal carinae indicated by multiple weak ridges; anteromedian clypeal margin broadly convex; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin approximately level with antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes straight, parallel. Psammophore absent. Palp formula 2,2. Mandibular teeth four; mandibles with sub-parallel inner and outer margins, striate; masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth approximately same size as t3 (four teeth present).
Mesosoma: Promesonotum shining and microreticulate throughout; (viewed in profile) promesonotum broadly convex; promesonotal setae two to six; standing promesonotal setae consisting of very short, incurved decumbent setae only; appressed promesonotal setulae well-spaced over entire promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum shining and microreticulate; propodeal dorsum flat throughout most of its length; propodeum smoothly rounded or with indistinct angle; standing propodeal setae consisting of one prominent pair anteriad, with other shorter setae very sparse or absent; appressed propodeal setulae well-spaced and sparse; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle absent or not visible. Propodeal lobes present as blunt-angled flanges.
Petiole and postpetiole: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex tapered; appearance of node shining and distinctly microreticulate; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1; anteroventral petiolar process present as a thin flange tapering posteriad; ventral petiolar lobe present; height ratio of petiole to postpetiole between 4:3 and 1:1; height-length ratio of postpetiole about 1:1; postpetiole shining and microreticulate; postpetiolar sternite not depressed at midpoint, its anterior end an inconspicuous lip or small carina.
Gaster: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.
General characters: Color yellowish, gastral tergites with brown infuscation in basal sector. Worker caste monomorphic.
Lectotype measurements ( M. vastator ): The physical condition and alignment of the worker does not permit ready measurements.
Lectotype measurements ( M. fragile ): HML 1.52 HL 0.56 HW 0.42 CeI 75 SL 0.48 SI 114 PW 0.23.
Other worker measurements: HML 1.39-1.48 HL 0.53-0.56 HW 0.42-0.45 CeI 78-81 SL 0.45-0.49 SI 105-111 PW 0.22-0.28 (n=8).
Queen description.- Head: Head square; vertex always planar; frons matt and uniformly reticulate-punctate; frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter setae or setulae, which are decumbent or appressed, longer setae thickest on vertex. Eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; eyes (in full-face view) set at about midpoint of head capsule; eyes (viewed in profile) set around midline of head capsule.
Mesosoma: Anterior mesoscutum smoothly rounded, thereafter more-or-less flattened; pronotum, mesoscutum and mesopleuron uniformly reticulate-punctate, punctations tending to form fine striolae on dorsum of mesoscutum; length-width ratio of mesoscutum and scutellum combined between 7:3 and 2:1. Axillae narrowly separated (i.e., less than width of one axilla). Standing pronotal/mesoscutal setae consisting of well-spaced, incurved, erect and semi-erect setae only; appressed pronotal, mescoscutal and mesopleural setulae well-spaced over entire surface. Propodeum uniformly reticulate-punctate; always smoothly rounded; propodeal dorsum convex; standing propodeal setae consisting of two or more pairs of prominent setae anteriad, with a few decumbent setae around declivitous face; appressed propodeal setulae well-spaced and sparse; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum; propodeal lobes present as bluntly angled flanges.
Wing: Wing not seen (queen dealated).
Petiole and postpetiole: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex tapered; appearance of node matt and reticulatepunctate; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1. Anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole about 1:1; height -length ratio of postpetiole about 4:3; postpetiole matt and reticulate-punctate; postpetiolar sternite forming a narrow wedge-shaped projection through strong convergence of its anterior and posterior ends.
Gaster: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.
General characters: Color orange-yellow, gaster brown, with large, yellow sector at apex of first tergite. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.
Holotype measurements ( M. contiguum ): HML 2.43 HL 0.68 HW 0.63 CeI 93 SL 0.62 SI 98 PW 0.73.
Other queen measurements: HML 2.37 HL 0.66 HW 0.62 CeI 94 SL 0.58 SI 94 PW 0.52 (n=1).
Remarks.- One of several tramp species in the M. destructor and M. salomonis groups found in Madagascar, M. pharaonis has recently been recorded from tropical dry forest and secondary rainforest. However, because of its anthropophilic nature, this ant probably has a wider distribution in Madagascar than these few (non-urban) records suggest.
I [introduced species]
Numerous workers and females from Stanleyville and Thysville (Lang and Chapin). This is the well-known, little, red house ant, spread by commerce throughout the world.
Records
(Map 24): Eastern Danubian Plain: Ruse, Shumen ( Atanassov and Dlusskij 1992 ); Sofia Basin: Sofia ( Atanassov 1965 , Atanassov and Dlusskij 1992 ); Thracian Lowland: Svilengrad ( Atanassov 1965 ), Plovdiv ( Atanassov and Dlusskij 1992 ); Strandzha Mt.: Malko Tarnovo ( Atanassov and Dlusskij 1992 ); Northern Black Sea coast: Varna ( Atanassov 1965 , Atanassov and Dlusskij 1992 ), Obzor vill. ( Atanassov and Dlusskij 1992 ); Southern Black Sea coast: Burgas, Tsarevo ( Atanassov 1965 , Atanassov and Dlusskij 1992 ), Sozopol, Ahtopol ( Atanassov and Dlusskij 1992 ).
The pharaoh ant (Monomorium pharaonis) is a small (2 mm) yellow or light brown, almost transparent ant notorious for being a major indoor nuisance pest, especially in hospitals.[1] A cryptogenic species, it has now been introduced to virtually every area of the world, including Europe, the Americas, Australasia and Southeast Asia. It is a major pest in the United States, Australia, and Europe.[2][3]
This species is polygynous—each colony contains many queens—leading to unique caste interactions and colony dynamics. This also allows the colony to fragment into bud colonies quickly.
Pharaoh ants are a tropical species, but they also thrive in buildings almost anywhere, even in temperate regions provided central heating is present.
Pharaoh workers are about 1.5 to 2 millimeters long, a little more than 1/16-inch. They are light yellow to reddish brown in color with a darker abdomen. Pharaoh ant workers have a non-functional stinger used to generate pheromones.[4] The petiole (narrow waist between the thorax and abdomen) has two nodes and the thorax has no spines. Pharaoh ant eyesight is poor and they possess on average 32 ommatidia.[5] The antennal segments end in a distinct club with three progressively longer segments.
Males are about 3mm long, black, winged (but do not fly). Queens are dark red and 3.6–5mm long. They initially have wings that are lost soon after mating, but do not fly.[6]
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, pre-pupal period three days and pupal period nine days. About four more days are required to produce sexual female and male forms. From egg to sexual maturity, it takes the pharaoh ant 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, pre-pupae and pupae.[3]
Each colony produces sexually reproductive individuals roughly twice a year. However, colonies raised in a laboratory can be manipulated to produce sexuals at any time of year. Colonies proliferate by "budding"[3] (also called "satelliting" or "fractionating"), where a subset of the colony including queens, workers and brood (eggs, larvae and pupae) leave the main colony for an alternative nest site.
Pharaoh ant colonies appear to prefer familiar nests to novel nests while budding. This suggests the ability for colonies to remember certain qualities of their living space. However, if the novel (unfamiliar) nest is of superior quality, the colony may initially move toward the familiar, but will eventually select the unfamiliar. The colony assumes the familiar nest is preferable, unless they sense better qualities in the novel nest. This decision-making process seeks to minimize the time the colony is without a nest while optimizing the nest the colony finally chooses.[7]
The number of available budding locations has a large effect on colony fragmentation. A large number of bud nests results in small colony fragments, indicating that the colony has the ability to control size and caste ratios. However, a minimum group size of 469 individuals appears preferred by the species. Amount of fragmentation does not have an effect on food distribution. After budding, nest units do not compete for resources, but rather act cooperatively. This is evolutionarily explained by the high amount of genetic relatedness among these nest units. In addition, major disturbances to the central nest cause the colony to abandon it and flee to a bud nest. Thus, nest units may exchange individuals after budding occurs, further explaining their cooperative behavior.[8]
In Australia, Monomorium species is particularly successful. This fact is particularly curious because of the presence of a very aggressive ant family, Iridomyrmex, which is quite proficient at interference competition. Iridomyrmex ants are able to quickly seek out food sources and prevent other ant species from reaching them. However, unlike other ant species, Monomorium species, despite their unaggressive nature and small size, are able to thrive even in areas where Iridomyrmex dominates. This success can be attributed to their efficient foraging strategy, and their novel use of venom alkaloids, repellant chemical signals. With these two behaviors, Monomorium species can rapidly monopolize and defend food sources.[9]
Pharaoh ants utilize three types of pheromones. One is a long-lasting attractive chemical that is used to build a trail network. It remains detectable even if the ants do not use the trail for several days. Pharaoh ants cease activity at night and begin each day of work at around 8 am, yet parts of the trail network are identical each day.[10] The second pheromone is also attractive, but will decay to imperceptible amounts in a matter of minutes without reapplication. This pheromone is useful in marking food sources, as these are unpredictable and the colony must be able to respond to environmental changes quickly. Individuals will not waste their time on an unprofitable trail route. The third pheromone is a repellant.[11] Pharaoh ants were the first species found to use a negative trail pheromone. If an individual finds an unprofitable area with little food or significant danger, it will release this repellant pheromone, which will warn others and cause them to look elsewhere. While positive pheromones indicating lucrative foraging sites are very common in social insects, the pharaoh ant's negative pheromone is highly unusual.[12] Like the food source marker, the negative pheromone is volatile, decaying roughly two hours after being emitted. It may even be insecticidal in some cases.[10] It is so powerful that an individual can detect it from 30 millimetres (1.2 in) away. Pharaoh ants utilize this pheromone near forks in the trail network, and an ant that detects it will begin to walk in a zigzag manner.[11]
Both the attractive and repellent pheromones are utilized in the decision-making an ant must make while foraging. The repellent pheromone is especially useful in the repositioning of trails after a new food source has been introduced. It also helps prevent ants from concentrating on an undesirable trail. Thus, the repellant pheromone makes the pharaoh ant a particularly efficient forager.[13] Despite their extreme importance, there is an adaptive value to using pheromones sparingly, as it streamlines communication during important decision-making situations, such as a nest migration.[14]
Pharaoh ants use a positive feedback system of foraging. Each morning, scouts will search for food. When one finds it, it will instantly return to the nest. This causes several ants to follow the successful scout's trail back to the food source. Soon, a large group will be upon the food. Scouts are thought to use both chemical and visual cues to remain aware of the nest location and find their way.[15] If the colony is exploring a new region, they employ a land rush tactic, in which a large number of foragers randomly search, constantly releasing pheromones.[10]
Even though M. pharaonis is most often thought an indoor pest, foraging has been found to be more prevalent outside. Even inside colonies were found to forage close to windows, indicating a propensity for outdoor environment.[1]
Even though scouts search independently, they use a distinct trail system that remains somewhat constant from day to day. The system consists of one to four trunk routes. Every scout uses one of these trunks in the beginning and end of its food search. In this way, the trunks get continuous chemical reinforcement and do not change much. Each trunk divides into many branch routes. These will change based on food availability.[15]
The organization of foraging trails is strongly affected by the health of the colony and the availability of food. Food deprivation induces a higher amount of foraging ant traffic, compared to a non-deprived population. If a food source is presented to the food deprived colony, this traffic was further increased, an indication of the pharaoh ant's recruitment tactic. If food is not present, a colony will extend its trails to a wider radius around the nest. Logically, number of trails and forager traffic is largest near a food source.[16]
While pheromones explain the pharaoh ant's foraging ability, each forager's capability to find its way back to the nest requires a different explanation. In fact, the pharaoh ant relies on geometry to show it the way home. Each fork in the trail system spreads at an angle between 50 and 60 degrees. When returning to the nest, a forager that encounters a fork will almost always take the path that deviates less from its current direction. In other words, it will never choose an acute angle that would drastically change its direction. Using this algorithm, each forager is able to find its way back to the nest. If the fork angle is experimentally increased to an angle between 60 and 120 degrees, M. pharaonis foragers were significantly less able to find their nest. This method of decision-making reduces the wasted energy that would result from traveling in the wrong direction and contributes to the pharaoh ant's efficiency in foraging.[17]
Upon scouts’ return with food, the queens will attempt to beg for their share. Depending on food availability and each individual's condition, a scout may refuse the queen's entreaties and even run away from her.[18] The decision of an individual to give up food to the queen may be beneficial in situations of plentiful food, as a healthy queen can reproduce and propagate the colony's genes. However, when food is highly scarce, an individual's own survival can outweigh this potential benefit. She will therefore refuse to give up food.
A queen may also feed on secretions from larvae. This creates a positive feedback loop in which more larvae will provide more food to queens who can in turn produce more larvae.[19]
If a large amount of larvae results in a surplus of secretions, pharaoh ants will store the excess in the gasters of a unique caste, the replete workers. Members of this group have enormous gasters and can regurgitate their stored food when needed. In this way, the colony has a cushion against food shortages.[20]
Pharaoh ants have a sophisticated strategy for food preference. They implement two related behaviors. The first is known as satiation. The workers will at first show a strong preference for a particular food type. However, if this food is offered alone, with no other options, for several weeks, workers will afterward show a distinct preference for a different type of food. In this way, the ants become satiated on a certain food group and will change their decision. The second behavior is called alternation. If given the continuous choice between food groups, pharaoh ants will tend to alternate between carbohydrate-rich foods and protein-rich foods. These satiation and alternation behaviors are evolutionarily adaptive. The decision to vary the type of food consumed ensures that the colony maintains a balanced diet.[21] Edwards & Abraham 1990's result is appropriate for highly competitive environments, and consistent with a high intake:expenditure ratio.[22]
Monomorium pharaonis, similar to other invasive ants, is polygynous, meaning its colonies contain many queens (up to 200). It is hypothesized that polygyny leads to lower levels of nestmate recognition in comparison to monogynous species due to the expected higher levels of genetic diversity. Because these colonies lack nestmate recognition, there is no hostility between neighbouring colonies, which is known as unicoloniality.[23]
Many invasive ants display unicoloniality. The adaptive value of this nonaggression among colonies has to do with avoiding unnecessary injury and allowing proper resource allocation, ensuring success for all the colonies. Low nestmate recognition, caused in part by polygyny, also has a biochemical basis in M. pharaonis. Cuticular hydrocarbons are compounds, often found on antennae, that allow for communication in many social insects. In ant species, these compounds play an especially key role in nestmate recognition. Differences in cuticular hydrocarbons are detected by other ant species, who respond accordingly. However, all pharaoh ant colonies have the same hydrocarbons on their antennae. This leads to ineffective nestmate recognition, and nonaggression between colonies.[23]
Pharaoh ant colonies contain many queens. The ratio of queens to workers is variable and dependent on the size of the colony. An individual colony normally contains 1,000–2,500 workers, but often a high density of nests gives the impression of massive colonies. In a small colony, there will be more queens relative to workers. In addition, individuals will be larger than those in a more populous colony.[24] This ratio is controlled by the workers in the colony. Larvae that will produce workers have characteristic hairs all over them, while larvae that will produce sexual males or females are bare. It is thought that workers can use these distinguishing features to identify larvae. Workers may cannibalize larvae in order to ensure a favorable caste ratio. This decision to cannibalize is largely determined by the present caste ratio. If plenty of fertile queens are present, for example, the workers may eat sexual larvae. The caste ratios are controlled in an attempt to maximize the growth of the colony.[25] For example, in a small colony, the ratio of queens to workers is increased. This in turn increases the potential for reproduction, allowing colony growth. Conversely, in a large colony, the high worker to queen ratio maximizes the foraging capacity of the nest, helping sustain the population size.[24]
The Pharaoh ant is a polygynous species that has a relatively low worker to queen ratio of around 12.86. This allows the pharaoh ants to be able to exert social control over the size of the colony and the size of each caste. In the average nest, there are around 170 ± 8 queens, which comprises around 5.2% of the total population, whereas there are around 2185 ± 49 workers, which make up around 66.6% of the population. This low worker to queen ratio is usually associated with swift changes in the nest and may be why pharaoh ants form many new nest buds quickly.[26] To branch out and form a new bud nest, pharaoh ants need a minimum of 469 ± 28 individuals, which explains how they proliferate so quickly.[27]
Mating for pharaoh ants occurs within the nests with males that are usually not from the colony which ensures genetic diversity. The queen can typically produce eggs in batches of 10 to 12 at once, but can lay up to 400 eggs every time she mates. The eggs that are produced take up to 42 days to mature from an egg to an adult. Each queen within the nest lives between 4 and 12 months.[28]
During copulation, sperm is transferred from male to female inside a spermatophore. There are several theories regarding the adaptive value of using a spermatophore. It contains certain chemicals that may inhibit the female's sex drive. Alternatively, it may physically plug the female's gonophore. In either explanation, the spermatophore prevents the female from reproducing with another male. In essence, the use of a spermatophore is evolutionarily favorable because it increases the probability of the male's genetic code being transferred to subsequent generations by lessening potential competition from other males.[29]
Pharaoh ant copulation, like that of many social insects, is harmful to the female. The penis valve contains sharp teeth, which latch onto a thick, soft cuticular layer in the female. This method of copulation too has an evolutionary basis. The teeth ensure sex lasts long enough for sufficient sperm transfer. Also, the pain caused to the female may, in some ways, lessen her desire to mate again.[29]
When the queen ant first moves to a new nest, she will rear the first group of workers. Once a worker threshold has been reached, resources will then be invested into new males and queens. When a new nest is formed, queens are not a necessity; workers can raise new queens after finding a suitable nest site.[24][27]
In pharaoh ant colonies new males and queen ants can be produced when the existing fertile queen is removed. When queens are absent, the workers in the nest can do two things: either rear existing sexual larvae or transport sexual larvae from other bud nests or from the main nest to its own nest. However, when there are fertile queens still within the nest, the worker ants will cannibalize the sexual larvae and will either reject or consume sexual larvae from other nests. On the other hand, the worker ants will always accept and nurture worker larvae from other nests.[25][30] Furthermore, according to Schmidt et al., polygamous species such as pharaoh ants will have higher resource allocations towards the female caste instead of the worker caste to ensure rapid growth of new budding colonies.[24]
When social ants encounter ants from another colony, behavior can be either aggressive or non-aggressive. Aggressive behavior is very commonly seen; the attacking worker usually bites the opponent at the petiole. In non-aggressive behavior, antennation occurs when the two ants meet. In the case of Monomorium pharaonis, behavior is almost always non-aggressive even when the ants are from different colonies and of different castes.[31] Very few cases exist where aggressive behavior is seen in these ants.
After foraging, pharaoh ants will wash themselves when a worker enters the cell. Pharaoh ants will also wash after a long feed. It has been proposed that washing has a hygienic value, keeping the nest area clean, staving off disease and disorder. Right before workers leave to forage, they also may wash themselves. However, in this instance the behavior is extremely violent, often causing the ants to fall over. It is thought that here, the washing behavior has no hygienic value and instead may be a displacement activity, a sign that the ants are deliberating whether or not to exit the nest.[18]
Budding is a major factor underlying the invasiveness of pharaoh ants. A single seed colony can populate a large office block, almost to the exclusion of all other insect pests, in less than six months. Elimination and control are difficult because multiple colonies can consolidate into smaller colonies during extermination programs only to repopulate later.
Pharaoh ants have become a serious pest in almost every type of building. They can feed on a wide variety of foods including grease, sugary foods, and dead insects. They can also gnaw holes in silk, rayon and rubber goods. Nests can be very small, making detection even more difficult.[2] They are usually found in wall voids, under floors, or in various types of furniture.[2] In homes, they are often found foraging in bathrooms or near food.[3]
It is recommended not to attempt extermination using insecticidal sprays and dusts because they will cause the pharaoh ants to scatter and colonies to split, although non-repellent residual insecticides have been reported to be effective.[32]
The recommended method to eliminate pharaoh ants is by the use of baits attractive to the species. Modern baits use insect growth regulators (IGRs) as the active substance; the ants are attracted to the bait by its food content, and take it back to the nest. Over a period of weeks the IGR prevents the production of worker ants and sterilizes the queen. Renewing the baits once or twice may be necessary.[32]
Pharaoh and other ants have also been exterminated with baits of 1% boric acid and sugar water.[33]
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{{cite journal}}: CS1 maint: uses authors parameter (link) The pharaoh ant (Monomorium pharaonis) is a small (2 mm) yellow or light brown, almost transparent ant notorious for being a major indoor nuisance pest, especially in hospitals. A cryptogenic species, it has now been introduced to virtually every area of the world, including Europe, the Americas, Australasia and Southeast Asia. It is a major pest in the United States, Australia, and Europe.
This species is polygynous—each colony contains many queens—leading to unique caste interactions and colony dynamics. This also allows the colony to fragment into bud colonies quickly.
Pharaoh ants are a tropical species, but they also thrive in buildings almost anywhere, even in temperate regions provided central heating is present.
