Key to Australian Tetramorium Species

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The following key to Australian Tetramorium is based on Bolton (1977)[1].

1

  • Antennae with 11 segments => 2
  • Antennae with 12 segments => 3

2

  • With petiole in profile the posterodorsal angle drawn out into a stout, blunt spine; basal angles of first gastral tergite with a narrow projecting semi-translucent flange which is continued as a margination down to sides of the basal third of the tergite => Tetramorium spininode
  • With petiole in profile the posterodorsal angle not projecting as a blunt spine; basal angles of first gastral tergite with a without a flange, not marginate down the basal third of the sides of the tergite => 4

3

  • Anterior clypeal margin with the median portion convex and notched or sharply indented medially => 5
  • Anterior clypeal margin with the median portion entire, not notched or sharply indented medially => 6

4

  • Large species, head width > 1.20 => 7
  • Smaller species, head width < 1.20, usually much less than this but rarely with HW up to about 1.10 => 8

5

  • Head and mesosoma yellow or orange-brown, the gaster either darker or lighter in colour than the head and mesosoma => 9
  • Entire body uniform dark brown to blackish brown => 10

6

  • Hairs on dorsal mesosoma sparse, short, stout and blunt apically; head and mesosoma (sometimes also gaster) yellow or yellowish brown => Tetramorium simillimum
  • Hairs on dorsal mesosoma numerous, of varying length, fine and generally acute apically; head and mesosoma dark brown, dark reddish brown or blackish brown => 11

7

  • Mandibles smooth and highly polished, with scattered small pits; base of first gastral tergite finely reticulate-punctate; anterior clypeal margin with a deep median notch; dorsal mesosoma without erect hairs => Tetramorium laticephalum
  • Mandibles longitudinally striate; base of first gastral tergite sharply but finely striate, the interstices reticulate-punctate; anterior clypeal margin without a median notch; dorsal mesosoma with erect hair => Tetramorium sjostedti

8

  • Anterior half to two-thirds of median portion of clypeus descending very steeply, almost vertical, this descending portion conspicuously transversely concave; median clypeal carina absent from descending portion which is unsculptured, the carina present only on the posterior third of the clypeus and the curve where it rounds into the steep anterior section => Tetramorium viehmeyeri
  • Anterior half to two-thirds of median portion of clypeus not shaped as above; median clypeal carina usually running the length of the clypeus or stopping just short of the anterior margin; anterior half of clypeus usually with other sculpture beside the median carina => 12

9

  • Erect hairs on dorsum of mesosoma branching near their bases into two or three filaments => Tetramorium lanuginosum
  • Erect hairs on dorsum of mesosoma simple, consisting of a single filament => 13

10

  • Dorsum of head sculptured with sparse but strong, regular longitudinal carinae or rugae, without any cross-meshes except for a few very close to the occiput, but often absent even here; ground sculpture between carinae on head very inconspicuous or absent, the surfaces smooth; basigatral costulae absent => Tetramorium validiusculum
  • Dorsum of head sculptured with rather irregular longitudinal rugae with numerous corss-meshes and with a conspicuous rugoreticulum posteriorly; ground sculpture between rugae on head superficial but fairly obvious; basigatral costulae generally present, sometimes very weak but rarely absent => Tetramorium pacificum

11

  • Lateral portions of pronotum very coarsely, sometimes irregularly, longitudinally or obliquely sulcate or exceptionally strongly rugose, the remainder of the sides of the mesosoma similarly sculptured, without reticulate-punctate interspaces; propodeal spines elongate, more than twice longer than the metapleural lobes, downcurved along their length => Tetramorium taylori
  • Lateral portions of pronotum reticulate-rugose or sides of mesosoma with reticulate-punctate sculpture present, or both; propodeal spines shorter, distinctly less than twice the length of the metapleural lobes, usually straight or feebly dinuate, only rarely downcurved => 14

12

  • Node of petiole in dorsal view transverse and roughly transversely rectangular in shape, distinctly broader than long => 15
  • Node of petiole in dorsal view not transverse, usually about as long as or longer than broad; in either case the node not roughly transversely rectangular in shape => 16

13

  • Mandibles finely and densely striate; longest hairs projecting dorsally from frontal carinae behind level of antennal insertions shorter than maximum diameter of eye; gaster always much darker in colour than head and mesosoma => Tetramorium bicarinatum
  • Mandibles smooth except for scattered hair-pits; longest hairs projecting dorsally from frontal carinae behind level of antennal insertions longer than maximum diameter of eye; gaster generally lighter in colour than head and mesosoma, only rarely the same or slightly darker => Tetramorium insolens

14

  • Mesopleuron with strong reticulate-punctate sculpture, any rugulae present are shallow and weakly defined; node of petiole in dorsal view slightly broader than long; dorsum of head with spaced-out low longitudinal rugulae, the spaces between them with conspicuous reticulate-punctate ground sculpture => Tetramorium deceptum
  • Mesopleuron coarsely rugose or sulcate, without or only with faint patches of punctulate sculpture; node of petiole in dorsal view distinctly longer than broad; dorsum of head with close-packed, sharply defined, high longitudinal rugulae, the spaces between them unsculptured or at most with very faint traces of punctures => Tetramorium ornatum

15

  • Dorsum of petiole and postpetiole densely punctulate with a few longitudinal rugulae; spaces between rugulae on dorsal mesosoma densely microscopically punctate => Tetramorium capitale
  • Dorsum of petiole and postpetiole smooth and highly polished or at most the petiole with traces of sculpture at the extreme lateral edges, the centre shining; spaces between rugulae on dorsal mesosoma shining, at most with very fiant suprficial reticulation or vestigial punctulation => Tetramorium confusum

16

  • Eyes large and situated well back on the sides of the head; head width about 0.78, maximum diameter of eye about 0.24 so that ocular diameter at maximum is about 0.32 X head width => Tetramorium megalops
  • Eyes smaller and situated at or close to the midlength of the sides of the head; maximum diameter of eye always less than 0.30 X head width; in larger species where ocular diameter approaches 0.24 the head width is always much great than 0.85 => 17

17

  • Spaces between rugulae on dorsum of head unsculptured or at most with faint, superficial reticulation or punctation, the surfaces shining; sides of head between eyes and frontal carinae not reticulate-punctate although some sculpture may be present; disc of postpetiole usually smooth, rarely sculptured => 18
  • Spaces between rugulae on dorsum of head completely filled with dense, very conspicuous reticulate-puncturation, the surfaces matt and generally quite dull; sides of head between eyes and frontal carinae densely reticulate-punctate, sometimes with other sculpture also; disc of postpetiole usually completely sculptured, rarely smooth => 19

18

  • Dorsal mesosoma mostly unsculptured and smooth, with only one or two low, very indistinct, almost effaced rugulae; metanotal groove very strongly impressed, the propodeal dorsum distinctly humped between the groove and the spines => Tetramorium andrynicum
  • Dorsal mesosoma strongly rugulose or reticulate-rugulose, the sculpture raised and conspicuous; metanotal groove at most only weakly impressed => 20

19

  • With the petiole in profile the dorsal length of the node grater than the height of the tergal portion so that the node appears relatively long and low => Tetramorium striolatum
  • With the petiole in profile the dorsal length of the node less than the height of the tergal portion so that the node appears relatively high and narrow => 21

20

  • Petiole node in dorsal view with the sides flat to feebly concave and the median sections of each side compressed towards one another so that the true dorsum has a niched-in median section => Tetramorium strictum
  • Petiole node in dorsal view with the sides convex and the median sections of each side not compressed towards one another; dorsum of node narrowest in front, becoming considerably broader posteriorly => 22

21

  • Hairs on promesonotum very short, thick and blunt, many of them strongly expanded toward the apex => Tetramorium thalidum
  • Hairs on promesonotum long, slender, often acute apically but if blunted they are not expanded apically => 23

22

  • Head and mesosoma dark brown to blackish brown; dorsum of petiole node with an unsculptured, shining median longitudinal strip; eyes distinctly shorter than the lengths of antennal segments 9 and 10 taken together => Tetramorium turneri
  • Head and mesosoma bright orange-red; dorsum of petiole node sculptured, without an unsculptured shining median longitudinal strip; eyes as long as the lengths of antennal segments 9 and 10 taken together => Tetramorium splendidior

23

  • Dorsal surface of postpetiole always strongly sculptured with rugulae and dense puncturation; frontal carinae differentiated only to level of the eyes, behind this they are suppressed or indistinguishable from the surrounding sculpture; head approximately same colour as mesosoma => Tetramorium impressum
  • Dorsal surface of postpetiole usually smooth, rarely with faint puncturation; frontal carinae strongly developed, reaching almost to the occiput; head always considerably darker in colour than mesosoma => Tetramorium fuscipes

References

  1. 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 (Natural History), Entomology, (2)36, 67–151.