Key to workers of the Socotra Archipelago, Yemen

This worker key is based on: Collingwood, C. A., Pohl, H., Guesten, R., Wranik, W. and van Harten, A. 2004. The ants (Insecta: Hymenoptera: Formicidae) of the Socotra Archipelago. Fauna of Arabia. 20:473-495.

The following key uses a limited number of morphological features, most of them observable at low magnification under a stereo microscope. Included in the key are the 18 species positively identified and an additional, yet undetermined species of Monomorium for which workers have been available.

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• Ants of the Socotra Archipelago
• Yemen

1

• Body with a single reduced or isolated segment (the petiole) between alitrunk and gaster . . . . . 2

• Body with two distinct segments (the petiole and the postpetiole) between alitrunk and gaster . . . . . 8

2

return to couplet #1

• Gaster with a strong projecting sting . . . . . Brachyponera sennaarensis

• Sting absent . . . . . 3

3

return to couplet #2

• Very small (HW < 0.45 mm), whitish base of gaster contrasting with brownish-black body . . . . . Tapinoma melanocephalum

• Larger (HW > 0.45 mm), body colouration different . . . . . 4

4

return to couplet #3

• Antennal insertions close to posterior clypeal margin . . . . . 5

• Antennal insertions distant from posterior clypeal margin (genus Camponotus) . . . . . 6

5

return to couplet #4

• Propodeum with two spines, petiole with two short projections dorsally . . . . . Lepisiota spinisquama

• Propodeum and petiole unarmed . . . . . Paratrechina longicornis

6

return to couplet #4

• Body colour dull black, posterior margin of head with several hairs; one size class of workers . . . . . Camponotus acvapimensis

• Body yellowish or bicoloured, posterior margin of head with two hairs at most; distinctly different small and large workers . . . . . 7

7

return to couplet #6

• Underside of hind tibiae bordered by at least six spiny hairs . . . . . Camponotus hova

• Hind tibiae only with fine subdecumbent hairs . . . . . Camponotus atlantis

8

return to couplet #1

• Propodeum simply rounded without a pair of teeth or spines (genus Monomorium) . . . . . 9

• Propodeum often with conspicuous spines, at least with a pair of blunt knobs . . . . . 13

9

return to couplet #8

• Propodeum dorsally with transversely striate sculpture (may be faint in small specimens), body colour either dark brown, or yellow, contrasting with predominantly dark gaster . . . . . 10

• Propodeum dorsally with very faint shagreened or punctate sculpture or unsculptured, body uniformly pale yellowish to brownish yellow . . . . . 11

10

return to couplet #9

• Head and alitrunk yellow, contrasting with predominantly dark gaster . . . . . Trichomyrmex destructor

• Whole body evenly dark brown . . . . . Trichomyrmex mayri

11

return to couplet #9

• Small to minute ants (HW < 0.40 mm) with small eyes (diameter less than 0.25 times the HW), petiolar and postpetiolar node not wider than long in dorsal view . . . . . 12

• Larger ants (HW > 0.50 mm) with comparatively larger eyes (diameter greater than 0.27 times the HW), petiolar and postpetiolar node clearly wider than long in dorsal view . . . . . Monomorium nimihil

12

return to couplet #11

• Antennae with 11 segments, head ventrally almost flat . . . . . Monomorium baushare

• Antennae with 12 segments, head ventrally mildly convex . . . . . Monomorium qarahe

13

return to couplet #8

• Dimorphic ants- major workers have broad heads and stout mandibles with two apical teeth and one basal tooth, minor workers have narrow heads and mandibles with seven or more evenly spaced teeth (genus Pheidole) . . . . . 14

• Monomorphic ants — mandibles With four or five evenly spaced teeth . . . . . 15

14

return to couplet #13

• Postpetiolar node distinctly higher than petiolar riode, petiole with a ventral translucent projection in major workers, head without any rugulose sculpture in minor workers . . . . . Pheidole lamellinoda

• Postpetiolar node at most as high as petiolar node, petiole without a ventral projection, usually some longitudinal rugae around eye in minor workers . . . . . Pheidole indica

15

return to couplet #13

• Body dorsum entirely without erect hairs (genus Cardiocondyla) . . . . . 16

• Body dorsum with several to many erect hairs (genus Tetramorium) . . . . . 17

16

return to couplet #15

• Propodeal spines distinct, acute (ratio of PSL to HL > 0.1) . . . . . Cardiocondyla emeryi

• Propodeal spines reduced to blunt denticles (ratio of PSL to HL < 0.08) . . . . . Cardiocondyla longiceps

17

return to couplet #15

• Dorsal outline of alitrunk evenly curved without metanotal groove, whole body covered in long fine acute hairs . . . . . Tetramorium lanuginosum

• Alitrunk outline rather flat with shallow metanotal groove, head and alitrunk with scattered short blunt hairs . . . . . 18

18

return to couplet #17

• Frontal carinae weak, antennal scrobes almost absent . . . . . Tetramorium caldarium

• Strong frontal carinae bordering conspicuous antennal scrobes . . . . . Tetramorium simillimum