Monomorium pharaonis (Linnaeus 1758)

Compiled by Richard Harris, Jo Berry, and Warwick Don

Biostatus: Introduced

Classification

Family:	Formicidae
Subfamily:	Formicinae
Tribe:	Solenopsidini
Genus:	Monomorium
Species:	pharaonis

Common name(s)

Pharaoh ant (Bosik 1997), Ie-hime-ari in Japan (WWW 1). Also referred to as Pharaoh's ant (Valentine & Walker 1991), Pharaoh's Trailing ant (WWW2)

Synonyms (WWW5)

Formica pharaonis Linnaeus, Formica antiguensis Fabricius, Myrmica contigua Smith, Myrmica domestica Shuckard, Myrmica fragilis Smith, Atta minuta Jerdon, Myrmica vastator Smith, Monomorium vastator (Smith), Myrmica pharaonis (Roger), [ Myrmica unifasciata Bostock].

Origin

Monomorium is a large genus with well over 300 species. Bolton (1987) observes that the main centres of speciation include Africa and Australia. According to Bolton (1987), M . pharaonis originates from tropical Africa. More recently, an Indian origin has come into favour. However, as Vail and Williams (1994) have observed, its widespread distribution "means its place of origin will probably always remain in doubt." A common tramp species frequently intercepted at the New Zealand border and spread with trade for well over a century (Bolton 1987). It is now virtually worldwide in distribution (Bolton 1987).

Distribution

Rarely collected, but specimens have be found in widely scattered localities, predominantly in hospitals, since the 1940s. Records include: AK: locality unspecified in 1952, 1955 (NZAC); Palmerston Buildings in 1959, 1960 (NZAC). TO: Taumaranui Hospital in 1951 (NZAC); Taumaranui in 1954 (NZAC). WN: St Helens Hospital (no longer exists) in 1941 (Te Papa); Hutt Hospital in 1954 (Te Papa; NZAC). MC: St Nicholas Hospital, Christchurch in 1979 (PANZ). An infestation was treated at the St John Ambulance station in Pitt St, Auckland about 3 years ago (V. Van Dyk pers. comm.). Specimens recently (14/2/03) collected on invasive ant surveillance baits at Mt Maunganui (but ID needs to be confirmed).

General Description

Identification

Antennae 12-segmented, including a 3-segmented club.

Diagnostic features of the worker

Total length 1.5 to 2.4 mm. Uniform pale yellow to lightish yellow brown, sometimes with a weak reddish tint (Bolton 1987). Gaster may be darker, often with a central paler patch on the dorsal (top) surface of the first segment. Eyes relatively small, with 5-7 ommatidia (usually 6) in the longest row. Prothorax with subangular shoulders. Groove between mesonotum and propodeum (about half way along thorax in lateral view) deeply impressed. No spines on body. Two nodes (petiole and postpetiole) present. Top of head with 4-5 pairs of erect setae. Dorsal thorax with 2-3 pairs of setae standing erect; petiole with 1-2 pairs and postpetiole with 2-3 pairs of backwardly directed hairs. First segment of gaster with numerous, evenly distributed setae in front of an apical transverse row on the dorsal surface. Head, thorax, petiole and postpetiole covered in weak, closely set punctures, appearing dull or subopaque. Clypeus, gaster, and mandibles shiny. A stinger is present but is rarely exserted.

[Monomorium pharaonis] head. Image: Eli M. Sarnat (Specimen:CASENT0171086). www.antweb.org Image — Monomorium pharaonis head. Image: Eli M. Sarnat (Specimen:CASENT0171086). www.antweb.org

Monomorium pharaonis profile. Image: Eli M. Sarnat (Specimen:CASENT0171086). www.antweb.org

[Monomorium pharaonis] dorsal view. Image: Eli M. Sarnat (Specimen:CASENT0171086). www.antweb.org Image — Monomorium pharaonis dorsal view. Image: Eli M. Sarnat (Specimen:CASENT0171086). www.antweb.org

Biology

An aggressive scavenger with a generalist diet, forming conspicuous trails in buildings (Deyrup et al . 2000).

Colonies with up to 300 000 workers with multiple queens (WWW3). Little aggression between colonies (unicolonial - Passera 1994). Colonies are polydomous (i.e. comprised of several nests) (Edwards 1986; Deyrup et al . 2000). Colonies are unstructured and very mobile; workers, along with larvae, pupae, and even a few queens, may move to new locations if disturbed or if the colony becomes too large, or conditions become unsuitable (WWW3). Queens live less than a year and workers are sterile (Passera 1994).

Primarily disperses by budding (Passera 1994). Mated queens also start colonies (WWW3) although there are no nuptial flights (Passera 1994). Their close association with humans and the location of nests within structures means humans easily transport this species. Documented cases of human-assisted spread include via loaves of bread from bakeries to hospitals in Germany (Eichler 1993) and via packaged food, in clothing or on pot plants (Eichler 1978).

Not found outside in temperate regions but survives in favourable microhabitats. Nests in household structures in any available cavity such as wall and cabinet voids, behind baseboards, behind refrigerator insulation, inside hollow curtain rods, or in the folds of sheets, clothes, or paper (Bolton 1987; WWW2). Generally inhabits only the best heated buildings, such as hospitals and homes with children where elevated temperatures are maintained throughout winter (Passera 1994). However, year-round survival of colonies was reported from a rubbish dump in Czechoslovakia due to favourable temperatures created by decaying refuse in the dump (Kohn & Vlcek 1986); and the microclimate in rat nests could favour the survival of M. pharaonis throughout the winter in temperate areas (Kohn & Vlcek 1982).

Pest Status

Reported as a major domestic pest internationally for well over a century (Bolton 1987), principally for its ability to "get into things" (WWW2). Rarely stings, but appears in huge numbers in kitchens, frequently infests rooms in homes and hospitals (Deyrup et al. 2000). Gnaws through packaging of food and infests contents (Bolton 1987). Transports pathogenic microbes in hospitals and there have been attacks on eyelids of infants, causing cutaneous lesions on premature new-borns (Fowler et al. 1993).

Reported as difficult to eradicate from buildings and survives most conventional household pest control treatment (WWW2). The spraying of a colony only causes budding to occur so this species is controlled almost exclusively with various baits (WWW2). Methoprene granular baits appear to be effective in controlling colonies (Edwards 1986; Lee et al. 2003).