Threat Level: Low

Tetramorium pacificum is a medium-sized dark colored ant that is most often encountered on vegetation. This species has a monomorphic worker caste with 12-segmented antennae, three-segmented antennal club, antennal scrobes, short antennal scapes that do not surpass the posterior margin of the head, a gradually sloped mesosoma, and strong propodeal spines. Like all myrmicines, T. pacificum has two waist segments and a gaster armed with a stinger.

There are five additional Tetramorium species that are spread across the Pacific Island region. Tetramorium pacificum can be distinguished from these by the combination of the following characters: (1) wave-shaped petiolar node, (2) long propodeal spines, (3) abundant long thin pilosity, and (4) uniformly dark color.

There are many other myrmicine genera that appear similar to Tetramorium. Pheidole species can be distinguished by their polymorphic worker caste. The major workers have disproportionately large heads, and the minor workers have long antennal scapes that extended beyond the posterior margin of the head and lack antennal scrobes. The mesosoma of the majors and minors are more steeply sloped than those of Tetramorium. Cardiocondyla species lack antennal scrobes. Wasmannia auropunctata has 11-segmented antennae with two-segmented antennal clubs.

Tetramorium pacificum has established populations outside of its native range, but it is not believed to cause significant damage to ecological or agricultural systems. The species is most often encountered on vegetation in disturbed or edge forest habitat.

Petiole with two waist segments (petiole & postpetiole)
Propodeal spines long
Antennae 12-segmented Antennal club with three segments
Antennal scrobe present
Slope of mesosoma even & gradual
Antennal insertion surrounded by a distinct elevated ridge
Shape of petiole node wave like
Hairs long and moderately abundant
Anterior margin of clypeus with notch present
Entire body uniform dark brown to black

Chart 1. Tetramorium pacificum vs. T. insolens, T. bicarinatum, T. lanuginosum
Chart 2. Tetramorium pacificum vs. T. tonganum, T. simillimum, T. caldarium

	T. pacificum	T. insolens	T. bicarinatum	T. lanuginosum
Head
Profile
Hairs	long & abundant	long & abundant	long & abundant	long & very dense
Petiole node shape	wave-shaped	wave-shaped	square	rounded
Color	uniform dark	uniform pale	gaster darker than rest of body	gaster darker than rest of body
	T. pacificum	T. insolens	T. bicarinatum	T. lanuginosum

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Chart 2. Tetramorium pacificum vs. T. tonganum, T. simillimum, T. caldarium

	T. pacificum	T. tonganum	T. simillimum	T. caldarium
Head
Profile
Propodeal spines	long	moderate	short	short
Hairs	long & abundant	long & abundant	short & sparse	short & sparse
Petiole node shape	wave-shaped	rounded	square	square
Anterior clypeal margin	present	absent	absent	absent
Size	moderate (> 3.5mm)	small (~ 2mm)	small (~ 2mm)	small (~ 2mm)
	T. pacificum	T. tonganum	T. simillimum	T. caldarium

• Antweb: specimen images, data & maps.
  
  
• Bolton, B. (1977) The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Oreintal and Indo-Australian regions, and in Australia. Bulletin of the British Museum (Natatural History) Entomology, 36, 67-151.
  
  
• Bolton, B. (1995) A new general catalogue of the ants of the world. Harvard University Press, Cambridge, Massachusetts, 504 pp.
  
  
• Wilson, E.O. & Taylor, R.W. (1967) The ants of Polynesia (Hymenoptera: Formicidae). Pacific Insects Monograph, 14, 1-109.