Monomorium (Hymenoptera: Formicidae) of the Arabian Peninsula with description of two new species, M. heggyi sp. n. and M. khalidi sp. n.

Measurements and indices

All measurements are in millimeters and follow the standard measurements of Bolton (1987) and Sharaf et al. (2018a).

CI = Cephalic Index (HW/HL × 100).

EI = Eye Index (EL/HW × 100).

EL = Eye Length; maximum diameter of eye in lateral view.

EM = Eye-Mandible Distance; distance between anterior margin of eye and mandibular insertion in lateral view.

HL = Head Length; maximum length of head, excluding mandibles in full-face view.

HW = Head Width; maximum width of head directly behind eyes in full-face view.

ML = Mesosoma Length (=Weber Length); length of mesosoma in lateral view); from a point at which pronotum meets cervical shield to posterior base of propodeal lobes or teeth.

PpH = Postpetiole Height; maximum height measured in lateral view.

PpL = Postpetiole Length; maximum length of postpetiolar node measured in dorsal view, from anterior margin to posterior margin.

PpW = Postpetiole Width; maximum width measured in dorsal view.

PtH = Petiole Height; maximum height measured in lateral view.

PtL = Petiole Length; maximum length of petiolar node measured in dorsal view, from anterior margin to posterior margin.

PtW = Petiole Width; maximum width measured in dorsal view.

PW = Pronotal Width; maximum width in dorsal view.

SI = Scape Index (SL/HW × 100).

SL = Scape Length, excluding basal neck.

TL = Total Length, sum of lengths of head, mesosoma, petiole, postpetiole and gaster in profile.

Abbreviations of museums

Abbreviations of natural history collections follow Brandão (2000) except for WML that follows Evenhuis (2020). The material on which this study is based is located and/or was examined at the following institutions:

BMNH The Natural History Museum, London, United Kingdom

CASC California Academy of Sciences, San Francisco, USA

KSMA King Saud University Museum of Arthropods, Riyadh, Kingdom of Saudi Arabia

LACM Los Angeles County Museum of Natural History, Los Angeles, CA, USA

MNHN Muséum National d’Histoire Naturelle, Paris, France

NHMB Naturhistorisches Museum, Basel, Switzerland

OXUM Hope Entomological Collections, University Museum, Parks Road, OXI 3PW Oxford, U.K

WML World Museum Liverpool, Liverpool, U.K

Nomenclatural acts

The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: urn:lsid:zoobank.org:pub:A7FFDF5C-6CD5-41CA-B106-BFF6BDFCB258; for Monomorium heggyi sp. n. is urn:lsid:zoobank.org:act:B57EC2EA-1781-4C19-ADFE-757C834E2774; and for Monomorium khalidi sp. n. is urn:lsid:zoobank.org:act:3B5BB529-D842-4146-B8F7-ACCAC9CD5BA7. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central and CLOCKSS.

Diagnosis of Arabian Monomorium

Members of the genus Monomorium can be recognized by combination of the following characters in the worker caste (Bolton, 1987, 1994; DuBois, 1986; Fisher & Bolton, 2016; Sparks, Andersen & Austin, 2019): monomorphic to polymorphic; antennae 10–12 segmented (most frequently 12), conspicuous 3-segmented club; mandibles with 3–4 teeth; palp formula 2,2, or 1,2; median clypeal seta conspicuous; median portion of clypeus raised, the raised portion usually longitudinally bicarinate; lateral portions of the clypeus not elevated as shield-like ridges anterior to the antennal toruli; frontal carinae distinct, but absent posterior to the medial arches of the antennal toruli; metanotal groove present, commonly impressed; propodeal dorsum usually unarmed and rounding into the declivity; propodeal spiracle usually circular, located at about the midlength of the sclerite; abdominal segment IV (metasomal III, gastral I) with posttergite overlapping poststernite.

Diagnosis of Arabian Monomorium species-groups

The M. monomorium species-group can be readily recognized by the following combination of characters in the worker caste (Sharaf et al., 2018a): monomorphic, with size variation; head longer than broad; mandibles smooth and masticatory margin armed with four teeth; antennae with 10–12 segments, terminating in a three-segmented club; median clypeal portion raised anteriorly and longitudinally bicarinate; eyes present with variable size, located in front of the midlength of the sides in full-face view, and with four or more ommatidia in the longest row; head smooth and shining; metanotal groove well-defined, with distinct cross-ribs; propodeal spiracle circular to subcircular; propodeal dorsum meeting declivity in a rounded angle; promesonotum and propodeal dorsum smooth; body pilosity variable but usually distinct; petiole, postpetiole and gastral tergites usually smooth.

The M. salomonis species-group can be diagnosed by the following character states in the worker caste (Bolton, 1987): monomorphic, with minor size variation; palp formula 2,2 or 1,2 in some minute species; mandibles usually sculptured; masticatory margins of mandibles armed with four teeth which decrease in size from apex to base; median clypeal portion raised, projecting anteriorly; cephalic dorsum usually sculptured, ranging from dense blanketing reticulate-punctuation to feeble superficial reticular patterning; eyes prominent of medium to large size, usually with six or more ommatidia in the longest row; eyes circular to oval in shape; head longer than broad; scapes usually relatively long (SI > 80); metanotal groove moderately impressed to absent; metanotal cross-ribs inconspicuous to absent; propodeal spiracle circular to subcircular; propodeum rounded to angular between dorsum and declivity; propodeal dorsum usually sculptured but never transversely striate; petiolar spiracle situated at the node or immediately in front of the anterior face of the node; body pilosity variable in distribution and density, but usually reduced on the head and mesosoma; mesosoma, petiole and postpetiole usually sculptured; first gastral tergite usually shagreenate or finely sculptured.

Synoptic checklist of Arabian Monomorium

Key to Arabian Monomorium based on the worker caste

Note: M. brunneolucidulum excluded due to lack of diagnostic characters.

• 1. Head smooth and glossy (Fig. 1A)2 (M. monomorium species-group)

• – Head sculptured, sculpture ranging from dense reticulate-punctate, longitudinal striations, to faint reticular patterning (Fig. 1B)10 (M. salomonis species-group)

• 2. Anterior median portion of clypeus strongly concave with two laterally projecting teeth (Fig. 1C)3

• – Anterior median portion of clypeus straight or feebly concave without raised ridges (Fig. 1D)4

• 3. Uniform dark brown to black; metanotal groove broadly and deeply impressed (Fig. 1E)M. carbonarium

• – Bicolored with yellow mesosoma contrasting with the black gaster; metanotal groove shallowly impressedM. rimae

• 4. Antenna 12-segmented5

• – Antenna 11-segmented7

• 5. Body pilosity clubbed; mesosoma, petiole and postpetiole distinctly sculptured (Fig. 1F)M. sarawatense

• – Body pilosity simple; mesosoma, petiole and postpetiole smooth and shining (Fig. 2A)6

• 6. Bicolored, with head and gaster dark brown to black contrasting the yellow or yellow-brown mesosoma and petiole; eyes small (EL 0.21–0.24 x HW) with six ommatidia in longest row, oval in profile (Fig. 2A)M. floricola

• – Uniform yellow; eyes relatively large (EL 0.30–0.32 x HW) with 8-9 ommatidia in longest row, in profile with convex dorsal margin and straight ventral margin (Fig. 2B)M. holothir

• 7. Mesosoma without standing hairs (Fig. 2C)8

• – Mesosoma with standing hairs (Fig. 2D)9

• 8. Eyes larger, with a ring of seven to eight ommatidia encircling a single row of 2 ommatidia, and in profile closer to mandibular insertions (EM 0.05); meso- and metapleuron smooth; petiole and postpetiole smooth and each with one pair of standing hairs (Fig. 2C)M. aeyade

• – Eyes smaller, with only 5–6 ommatidia total, and in profile further away from mandibular insertions (EM 0.09–0.11); meso-and metapleuron finely shagreened; petiole and postpetiole superficially shagreened and without standing hairs (Fig. 2E)M. mohammedi

• 9. Mesosoma with two pairs of standing hairs, one on pronotal corners and one on propodeum (Fig. 2F)M. clavicorne

• – Mesosoma with several pairs of standing hairs, about 10 pairs (Fig. 2D)M. exiguum

• 10. Underside of head with crowded J-shaped hairs forming a distinct psammophore (Fig. 3A)M. barbatulum

• – Underside of head without long J-shaped hairs, psammophore absent11

• 11. Mesosoma without standing hairs12

• – Mesosoma with standing hairs25

• 12. Uniform yellow, brown, or yellow-brown, gaster not darker than mesosoma13

• – Bicolored, with gaster distinctly darker than mesosoma18

• 13. Metanotal groove shallowly impressed or indistinct (Fig. 3B)14

• – Metanotal groove deeply impressed (Fig. 3C)15

• 14. Small yellow species (TL 1.7, HL 0.45–0.48, HW 0.34–0.36, SI 92–97); cephalic surface with vestigial or superficial reticular patterning, almost entirely effaced; petiole and postpetiole without standing hairs; (Fig. 3B); first gastral tergite completely glabrous, that is, without standing hairs (Fig. 3B)M. heggyi sp. n.

• – Large brown species (TL 2.20–2.75, HL 0.57–0.65, HW 0.51, SI 93–103); cephalic surface with fine and dense reticulate-rugulose sculpture; petiole and postpetiole each with two pairs of standing hairs (Fig. 3D); first gastral tergite always with several pairs of standing hairs (Fig. 3D)M. harithe

• 15. Eyes located nearly at the midlength of head as seen in full-face view (Fig. 3E); eyes smaller, with 5 ommatidia in longest row; posterior margin of head distinctly concave in full-face view (Fig. 3E)M. elghazalyi

• – Eyes located nearly behind or at head midlength as seen in full-face view (Fig. 3F); eyes distinctly larger, with 10–14 ommatidia in longest row; posterior margin of head concave or linear in full-face view16

• 16. Underside of head without long, standing hairs (Fig. 4A)M. dirie

• – Underside of head with numerous pairs of long, standing hairs (Fig. 4B)17

• 17. Yellow; scapes just reaching posterior margin of head when laid back; body pilosity abundant over entire bodyM. nimihil

• – Brown; scapes surpassing posterior margin of head by about half the length of the pedicel when laid back; body pilosity distinctly reduced over entire surface, mesosoma with a single pair of hairs on propodeum, while the petiole, postpetiole, and gaster are bareM. salomonis

• 18. First gastral tergite without standing hairsM. moathi

• – First gastral tergite with hairs either scattered on tergite surface or apically on the posterior margin19

• 19. Scapes when laid back from their insertions reach or surpass posterior margin of head in full-face view20

• – Scapes when laid back from their insertions fail to reach posterior margin of head in full-face view21

• 20. Propodeal dorsum in profile meeting declivity forming two blunt, slightly projecting angled bosses (Fig. 4C)M. subdenticorne

• – Propodeal dorsum in profile meeting declivity in a continuous curve (Fig. 4D)M. bicolor

• 21. Petiole in the form of a high triangle in profile with anterior face appears as a continuous line sloping anteriorly (Fig. 4E)M. acutinode

• – Petiole broadly rounded with anterior face sloping downward and then anteriorly to the peduncle (Fig. 4F)22

• 22. Head faintly superficial sculptured, slightly shiningM. venustum

• – Head densely and finely reticulate to reticulate-shagreenate23

• 23. Small (TL 2.3–2.4, HL 0.60–0.63, HW 0.43–0.45, PW 0.30–0.31, ML 0.66–0.70); mesosoma and gaster approximately of the same color, the two not strongly contrastingM. carbo

• – Larger (TL 3.1–3.4, HL 0.70–1.04, HW 0.54–0.88, PW 0.36–0.53, ML 0.88–1.24); mesosoma and gaster conspicuously differently colored, gaster usually darker24

• 24. Eyes with 12–14 ommatidia in longest row; metanotal groove deeply impressed (Fig. 5A); postpetiole with two to three pairs of backward directed hairsM. areniphilum

• – Eyes with 9–11 ommatidia in longest row; metanotal groove feebly impressed (Fig. 5B); postpetiole with a single pair of backward directed hairsM. subopacum

• 25. Large (TL ≥ 3.8, HW > 0.75)26

• – Smaller (TL 2.2–3.2, ≤ HW 0.67)28

• 26. Entirely yellowish; mesosoma rather flat with a shallow oblique metanotal groove (Fig. 5C)M. luteum

• – Gaster dark contrasting with red mesosoma; metanotal groove steeply angled (Fig. 5D)27

• 27. Head smooth with superficial sculpture; the first of the three segments forming the club being shorter than the second (Fig. 5E); head in full-face view with feebly but distinctly convex sides; head in full-face view with eyes fail or just break head sides (Fig. 5E)M. niloticum

• – Head completely finely striate (Fig. 5F); the first of the three segments forming the club nearly subequal to the second (Fig. 5F); head in full-face view with straight sides; head in full-face view with eyes break sides (Fig. 5F)M. riyadhe

• 28. Mesosoma red, contrasting with dark gaster29

• – Mesosoma pale brown to black, concolorous with gaster34

• 29. Mesosoma hairs restricted to one pair on pronotum30

• – Mesosoma with several pairs of hairs scattered over whole dorsum31

• 30. Head and mesosoma dull red, gaster brown; scapes reaching posterior head margin when laid back (Fig. 6A); cephalic surface with vestigial sculptures; posterior margin of head with a single pair of hairs (Fig. 6A); propodeum in profile with dorsum making an obtuse angle with declivity (Fig. 6B)M. hanaqe

• – Head and mesosoma bright orange red, gaster black; scapes not reaching posterior head margin when laid (Fig. 6C); cephalic surface densely punctate; posterior margin of head without hairs except for appressed pubescence (Fig. 6C); propodeum in profile with dorsum making a continuous curve with declivity (Fig. 6D)M. jizane

• 31. Propodeal dorsum with a single pair of standing hairs32

• – Propodeal dorsum with at least three pairs of standing hairs33

• 32. Scapes when laid back from their insertions reach posterior margin of head in full-face view (Fig. 6E); cephalic surface densely punctate (Fig. 6E); gaster smooth and shining (Fig. 6F)M. fayfaense

• – Scapes when laid back from their insertions fail to reach posterior margin of head in full-face view (Fig. 7A); cephalic surface with vestigial sculpture (Fig. 7A); gaster finely densely shagreened and dull (Fig. 7B)M. knappi

• 33. Whole body with abundant fine hairs (Fig. 7C); with head in full-face view outer margins of eyes break head sides (Fig. 7D)M. nitidiventre

• – Body pilosity limited and stiff (Fig. 7E); promesonotum with five to six pair of standing hairs, promesonotum and propodeum each with three pairs; petiole and postpetiole each with two-three pairs; with head in full-face view outer margins of eyes fail to break head sides (Fig. 7F)M. khalidi sp. n.

• 34. Whole body including gaster densely sculptured and dull35

• – Gaster at least more or less shining with superficial sculpture37

• 35. Head, mesosoma, and waist segments very light brown or yellow; hairs on mesosoma scattered (Fig. 8A)M. pharaonis

• – Head, mesosoma, and waist segments conspicuously of darker brown or black; mesosoma hairs mainly or entirely on pronotum (Fig. 8B)36

• 36. Body color brown; larger species (TL 3.1–3.3, HW 0.70); scapes long, surpassing posterior head margin by about the length of the pedicel when laid back (Fig. 8C); head in full-face view with convex sides (Fig. 8C)M. suleyile

• – Body color uniformly black; smaller species (TL 2.7–2.9, HW 0.56); scapes shorter, just reaching posterior head margin when laid back of head (Fig. 8D); head in full-face view with parallel sides (Fig. 8D)M. mahyoubi

• 37. Whole body glossy, nodes and gaster brilliantM. dammame

• – At least mesosoma with close punctate sculpture38

• 38. Underside of head with numerous hairs (12–16), the longest exceeding the maximum eye length (Fig. 8E)M. tumaire

• – Underside of head with fewer hairs, none as long as maximum eye length (Fig. 8F)39

• 39. Head finely and densely punctate, general appearance dull40

• – Head feebly superficially sculptured, relatively but distinctly shining41

• 40. Smaller species (TL 2.4–2.7); clypeal border feebly concave to straight with a very small median notch or none (Fig. 9A); mesonotum straight in profile (Fig. 9B)M. gallagheri

• – Larger species (TL > 3.0); clypeus with a distinct anteromedian notch (Fig. 9C); mesonotum distinctly convex in profile (Fig. 9D)M. buxtoni

• 41. Scapes distinctly short, surpassing compound eye posterior margins by only about the length of the first funicular segmentM. buettikeri

• – Scapes longer, reaching posterior head margin42

• 42. Color dark brown to black; smaller species (TL 2.40–2.75, C1 78–91); metanotal groove shallowly impressedM. abeillei

• – Color light to median brown; larger species (TL 3.2, CI [69–71]); metanotal groove distinctly impressedM. asiriense

New taxonomic treatments

New site records include, when available, geo-coordinates (°N, °E), elevation (m), collection date, collector, and number worker (w) and queen (q) specimens.

Monomorium abeillei André, 1881

(Figs. 10A–10C)

Monomorium abeillei André, 1881: 531 (footnote) (w.) Israel. Palearctic. (MNHN, CASENT0915411). [Image of lectotype worker examined]. [Also described as new by André, 1881: 67.].

Combination in Monomorium (Xeromyrmex): Emery, 1922: 177; subspecies of Monomorium salomonis: Forel, 1910a: 23; Hamann & Klemm, 1967: 413; revived status as species: Collingwood, 1985: 269; Collingwood & Agosti, 1996: 340.

Monomorium wahibiense Collingwood & Agosti, 1996: 357 (w.) Oman. Palearctic. [NHMB], CASENT0913864. Syntype worker, Oman, Wahiba dunes (21.vii.1985, M. D. Gallagher) [examined] syn. n.

Material examined. KSA: Asir Province: Raydah (18.198, 42.410, 2,443 m, 22.ii.2014, M.R. Sharaf, 3w); Raydah (18.204, 42.412, 2,820 m, 21.ii.2014, M.R. Sharaf, 6w); Riyadh Province: Huraymila, Buaythiran (25.149, 45.950, 07.ii.2011, M.R. Sharaf, 2w); Rawdhat Khureim (25.383, 47.277, 618 m, 02.vi.2013, S. Salman, 6w); Rawdhat Khureim (25.425, 47.235, 579 m, 09.i.2015, S. Salman, 12w); Dirab, KSU research station (24.419, 46.654, 568 m, 05.xii.2013, S. Salman, 1w); Wadi Hanifa (24.670, 46.654, 657 m, 14.ii.2014, S. Salman, 3w); Mezahmyia (24.472, 46.239, 633 m, 25.i.2014, S. Salman, 1w); Mezahmyia (24.466, 46.251, 648 m, 29.xi.2014, S. Salman, 1w); Al Hayer (24.546, 46.742, 647 m, S. Salman, 2w); Al Hayer (24.557, 46.744, 589 m, 11.iv.2014, S. Salman, 6w); Runnah (25.571, 46.973, 615 m, 12.iv.2014, S. Salman, 1w); Dawademi (24.478, 44.364, 1,027 m, 18.iv.2014, S. Salman, 1w); Dawademi (24.583, 44.323, 966 m, 16.i.2015, S. Salman, 3w); Dawademi (24.538, 44.355, 999 m, 16.i.2015, S. Salman, 1w); Afif (23.766, 42.840, 1,015 m, 19.iv.2014, S. Salman, 6w); Afif (24.302, 43.688, 951 m, 19.iv.2014, S. Salman, 1w); Afif (23.900, 42.081, 1,052 m, 17.i.2015, S. Salman, 15w); Afif (23.957, 42.976, 1,059 m, 17.i.2015, S. Salman, 1w); Irgah (24.6710, 46.593, 625 m, 19.i.2015, S. Salman, 2w); Thadiq (25.294, 45.871, 735 m, 26.iv.2014, S. Salman, 1w); Quwayia (24.047, 45.244, 854 m, S. Salman, 7w); Shaqra (25.326, 45.233, 710 m, 30.v.2014, S. Salman, 9w); Shagra (25.230, 45.319, 703 m, 24.i.2015, S. Salman, 1w); Shaqra (25.270, 45.291, 712 m, 23.i.2015, 2w); Durma (24.607, 46.130, 646 m, 30.i.2015, S. Salman, 1w); Majma’a (25.880, 45.365, 730 m, 07.ii.2015, S. Salman, 5w); Kharrarah (24.392, 46.244, 726 m, 08.iv.2015, S. Salman, 15w); Al Ghat (26.066, 44.919, 653 m, 31.x.2015, S. Salman, 1w); Hawtet Sudeir (25.592, 45.612, 732 m, 31.i.2015, S. Salman, 1w); KSU campus (24.737, 46.618, 662 m, 29.ii.2012, K. Mahmoud, 1w); Dirab (24.419, 46.654, 804 m, 18.ix.2014, S. Salman, 9w); Hareeq (23.614, 46.054, 689 m, 22.ii.2015, S. Salman, 1w); Quwayia (24.058, 45.245, 846 m, 29.xi.2014, S. Salman, 1w); Salboukh (25.078, 46.347, 716 m, 26.xii.2014, S. Salman, 8w); Jazan Province: Sajid Island, Al-Sajid (16.860, 41.932, 05.iii.2017, U. Abuelgheit, 1w).

Remarks. Monomorium wahibiense is represented by a single worker deposited in WML and accompanied by a red card and handwritten label by C. Collingwood indicating that this specimen represents the syntype. The label’s data are consistent with the data for the type in the original description in terms of collecting locality (Oman, Wahiba sand) and collector (M.D. Gallagher), but not the collection date, which we consider a typographical error.

Comparing the mentioned type material with the image of the type material of M. abeillei André, we found the two species share the same morphological characters, which can be summarized as follow: scapes relatively short, when laid back from their insertions just reaching posterior head margin; eyes of moderate size with about 10–11 ommatidia in longest row; cephalic surface between frontal lobes faintly striated whereas in some individuals the striations are absent; promesonotum and mesonotum forming continuous flat line in profile; mesosoma with single pair of standing hairs on pronotal humeral angles; metanotal groove feebly impressed; petiole with single pair of backward directed hairs; postpetiole with two pairs. However, the eyes are slightly smaller in M. abeillei, and the central cephalic sculpture is feebly microreticulate-striolate than in the relatively large-eyed M. wahibiense and the superficially sculptured cephalic surface but we consider these two traits as variable characters. Herein, we propose treating M. wahibiense as a junior synonym of M. abeillei André.

Geographic Distribution. Monomorium abeillei is originally described from Israel and recorded from several countries in the Middle East, including the Arabian Peninsula (KSA, Kuwait, Oman and Yemen) (Collingwood, 1985, Collingwood & Agosti, 1996), Iran (Paknia et al., 2008), Israel (Vonshak & Ionescu-Hirsch, 2009) and North Africa (Borowiec, 2014).

Monomorium areniphilum Santschi, 1911

(Figs. 11A–11C)

Monomorium salomonis var. areniphila Santschi, 1911: 84 (w.) Tunisia. Palearctic. [NHMB], CASENT0249829, [Syntype worker, examined].

Emery, 1915: 378 (q.); combination in Monomorium (Xeromyrmex): Emery, 1922: 177; subspecies of Monomorium salomonis: Santschi, 1936: 50; raised to species: Collingwood, 1985: 269; senior synonym of Monomorium lepineyi, Monomorium pullula: Bolton, 1987: 336.

Senior synonym of Monomorium fezzanense Collingwood & Agosti, 1996: 346 (w.) Saudi Arabia. Afrotropic. [NHMB], Syntype worker, Saudi Arabia, 31 km NW Tabuk (24.iv.1979, CASENT0913557) [examined] syn. n.

Senior synonym of Monomorium hemame Collingwood & Agosti, 1996: 348 (w.) Kuwait. Palearctic. [WML], holotype worker, Kuwait, Umm Al-Hemam (9.III.1988, W. Biittiker, CASENT0922316) [examined]; paratype worker, Saudi Arabia, Uyaynah (01.IV 1976, W. Biittiker, CASENT0913800) [examined] syn. n.

Senior synonym of Monomorium marmule Collingwood & Agosti, 1996: 349, fig. 21 (w.) OMAN. Palearctic. Paratype worker, Oman, Minririb (14.i.1986, M.D. Gallagher, CASENT0913824, NHMB) [examined] syn. n.

Remarks. A thorough examination of the type material of M. fezzanense, M. hemame, M. marmule, and M. areniphilum yielded no evidence for heterospecificity; they are indistinguishable. All four taxa share the following characters: median portion of anterior clypeal margin shallowly concave; eyes large with 12–15 ommatidia in longest row; promesonotum and anterior portion of mesonotum in profile feebly convex; posterior portion of mesonotum sloping steeply to broadly and deeply impressed metanotal groove; mesosoma without hairs; petiole with single pair of backward directed hairs; postpetiole with two pairs of hairs.

Herein M. fezzanense, M. hemame, and M. marmule are treated as junior synonyms of M. areniphilum. It is worth mentioning that in the original description of M. marmule, Collingwood & Agosti (1996) gave a brief differential diagnosis with M. areniphilum based on variable characters such as the presence of mesosomal pubescence, the petiole and postpetiole color and pilosity.

Geographic Distribution. A species originally described from Tunisia and recorded from most countries of the Arabian Peninsula including KSA, Kuwait, Oman, and Yemen (Collingwood, 1985; Collingwood & Agosti, 1996), and the UAE (Collingwood et al., 2011). It is also reported from North Africa and the Afrotropical Region (Bolton, 1987).

Monomorium barbatulum Mayr, 1877

(Figs. 12A–12C)

Monomorium barbatulum Mayr, 1877: 17 (w.) Kazakhstan. Palearctic.

Material examined. KSA: Riyadh Province: Zulfi (26.367, 44.986, 670 m, 18.i.2014, Al Dhafer et al., 1w: CASENT0922263, KSMA).

Geographic Distribution. This species was originally described from Kazakhstan and recorded from Oman (Collingwood, 1985; Collingwood & Agosti, 1996), the UAE (Collingwood et al., 2011), Turkey (Kiran & Karaman, 2020), Israel (Vonshak & Ionescu-Hirsch, 2009). The present material represents a new record to the KSA.

Remarks. Monomorium barbatulum looks similar to some members of the genus Trichomyrmex in terms of the following characters: polymorphic with 12-segmented antennae that lacking the well-defined terminal club; masticatory margin of mandibles armed with 3–4 teeth; propodeum unarmed. However, M. barbatulum lacks a critical diagnostic character for the genus Trichomyrmex which is the absence of the transverse striations on propodeal dorsum. With the availability of more material for a comprehensive taxonomic investigation, together with additional molecular evidence(s), we will be able to resolve properly the taxonomic status of the species.

Monomorium bicolor Emery, 1877

(Figs. 13A–13C)

Monomorium bicolor Emery, 1877: 368 (w.) Eritrea. Afrotropic.

Senior synonym of Monomorium phoenicum Santschi, 1927e: 242 (w.q.) Lebanon. Palearctic. Syntype worker, Lebanon, Beyroth (05.viii.1933, Santschi, CASENT0249831, NHMB) [examined] syn. n.

Material examined. KSA: Asir Province: Almajardah, Wadi Eltalalei (19.003, 41.732, 223 m, 10.xi.2012, M.R. Sharaf, 1w); Wadi Shahadan (17.472, 42.856, 452 m, 13.xi.2012, M.R. Sharaf, 13w, (1w, CASENT0906396); Allaith, Adam, Wadi Elarj (20.453, 40.816, 450 m, 09.xi.2012, M.R. Sharaf, 45w, 1w: CASENT0906395, 1q: CASENT0906394); Wadi Aljora, near Abadan (17.293, 43.070, 465 m, 12.xi.2012, M.R. Sharaf, 2w); Almajardah, Wadi Bagara (18.793, 42.019, 436 m, 10.xi.2012, M.R. Sharaf, 2w); Jazan Province: Abu Arish (17.013, 42.802, 90 m, 10.iv.2012, M.R. Sharaf, 11w); Sabia (17.107, 42.650, 43 m, 09.iv.2012, M.R. Sharaf, 23w); Jazan (16.97627, 42.61743, 38 m, 12.iv.2012, M.R. Sharaf, 12w); Al Bahah Province: Dhi Ayn Archeological village (19.930, 41.443, 741 m, 18.v.2011, M.R. Sharaf, 3w); Wadi Gonouna (19.429, 41.605, 353 m, 12.v.2011, M.R. Sharaf, 10w: KSMA).

Remarks. The type material of M. bicolor and M. phoenicum are clearly conspecific. They share the same diagnostic characters as follow: scapes relatively long, when laid back from their insertions surpassing posterior head margin by about length of pedicel; head in full-face view with eyes just breaking sides; cephalic surface dull, finely and densely punctate; median anterior clypeal margin distinctly concave; area between frontal carinae finely longitudinally striated; mesosoma without standing hairs; metanotal groove acutely impressed; propodeal dorsum in profile meeting declivity in continuous curve; petiole and postpetiole each with single pair of back directed hairs; first gastral tergite with hairs scattered over tergite surface; biocolored species, with head, mesosoma, petiole and postpetiole yellow-red or yellow-brown, gaster dark brown to black. Herein, we propose M. phoenicum as a junior synonym of M. bicolor.

Geographic Distribution. Monomorium bicolor was originally described from Eritrea and is a widespread species commonly encountered in open, sandy areas through the Afrotropical Region (Bolton, 1987). In the Arabian Peninsula, it is known from the KSA and the UAE (Collingwood, 1985; Collingwood & Agosti, 1996; Collingwood et al., 2011).

Monomorium brunneolucidulum Collingwood & Agosti, 1996

Monomorium brunneolucidulum Collingwood & Agosti, 1996: 343. Oman. Palearctic.

Remarks. In their brief original description of the enigmatic species M. brunneolucidulum from Oman, Collingwood & Agosti (1996) neither gave successful diagnostic characters nor illustrations for species recognition. In addition, the type-material is apparently lost. Due to a lack of type material and species diagnostic characters, it is impossible to confirm the identity of the species. Until the type material of this species is available we prefer to treat it as a nomen dubium.

Monomorium floricola (Jerdon, 1851)

(Figs. 14A–14C)

Atta floricola Jerdon, 1851: 107 (w.) India. Indomalaya.

Forel, 1893: 388 (q.m.); Wheeler, 1905: 88 (q.m.); Donisthorpe, 1914: 136 (gynandromorph); Crawley, 1920: 217 (gynandromorph); Wheeler & Wheeler, 1955c: 121 (l.). Combination in Monomorium: Mayr, 1879: 671.

Senior synonym of Monomorium poecilum: Emery, 1894d: 151.

Senior synonym of Monomorium specularis: Mayr, 1879: 671.

Senior synonym of Monomorium cinnabari: Wheeler, 1913: 486.

Senior synonym of Monomorium floreanum: Brown, in Linsley & Usinger, 1966: 175.

Senior synonym of Monomorium angusticlava: Bolton, 1987: 390.

Senior synonym of Monomorium impressum: Bolton, 1987: 390.

Senior synonym of Monomorium floricola furina: Heterick, 2006: 122.

Senior synonym of Monomorium floricola philippinensis: Heterick, 2006: 122.

Material examined. Oman: Dhofar Province: Ayn Dirbat (17.106, 54.453, 207 m, 17.xi.2017, M.R. Sharaf, 4w: KSMA, 1w: CASENT0922876, CASC).

Geographic Distribution. This species was originally described from India. It is a successful tramp species of putative Southeast Asian origin that is widely distributed throughout tropical and subtropical regions worldwide (Deyrup, Davis & Cover, 2000; Wetterer, 2010a). The present material represents a new record for Oman and the Arabian Peninsula.

Monomorium harithe Collingwood & Agosti, 1996

(Figs. 15A–15C)

Monomorium harithe Collingwood & Agosti, 1996: 347 (w.) Saudi Arabia. Afrotropic. Holotype worker: Saudi Arabia, desert near Najran, 17.533, 44.000, 10.iv.1983, C.A. Collingwood, CASENT0922335, WML, [examined] syn. n.

Monomorium najrane Collingwood & Agosti, 1996: 352 (w.) Saudi Arabia. Afrotropic, Holotype worker: Saudi Arabia, Najran, semi desert, iv.1984, C.A. Collingwood, CASENT0922335, WML, [image examined] syn. n.

Previous records. KSA: Riyadh (24.714, 46.675, 21.i.1980, A.H. Talhouk, 2w); Yemen: Taiz (13.578, 44.018, 20.iii.1993, C.A. Collingwood, 2w).

Remarks. Monomorium harithe was described from the KSA and Yemen, while M. najrane was described from Najran (KSA) near the Saudi-Yemeni borders (Collingwood & Agosti, 1996). The comparison of the type material of the two species reveals a straightforward synonymy. The two species share the following characters: anterior median clypeal margin distinctly concave; scapes distinctly short, when laid back from their insertions failing to reach posterior head margin; mesosoma without standing hairs; metanotal groove feebly impressed but distinct; propodeal dorsum with distinct furrow; mesosoma, petiole and postpetiole finely and densely punctate; petiole and postpetiole each with single pair of back directed hairs; gaster smooth and shining. In addition, the two species share common body measurements (e.g., HW 0.51; SL 0.53).

Geographic Distribution. This Arabian endemic species is only known from the KSA and Yemen (Collingwood & Agosti, 1996).

Monomorium heggyi Sharaf, sp. n.

(Figs. 16A–16C)

Holotype pinned worker. KSA: Al Bahah Province: Shada Al A’la Mountain (19.877, 41.311, 897 m, Al Dhafer et al., MRS0261, CASENT0746641, KSMA).

Paratype pinned workers. KSA: Al Baha Province: Shada Al A’la Mountain (19.877, 41.311, 897 m, 04.vi.2014, M. R Sharaf, 4w, 1w: CASENT0746641); Shada Al A’la Mountain (19.863, 41.301, 1,225 m, 08.xii.2014, Al Dhafer et al., 6w, 1w: CASENT0922301); Shada Al A’la Mountain (19.843, 41.312, 1,666 m, 23.viii.2014, Al Dhafer et al., 1w: CASENT0906391); Shada Al A’la Mountain (19.877, 41.311, 897 m, 04.vi.2014, M.R. Sharaf, MRS0261, 2w); Shada Al A’la Mountain (19.877, 41.311, 897 m, 23.viii.2014, M.R. Sharaf, MRS0261, 1w: CASENT0746641); Shada Al A’la Mountain (19.863, 41.301, 1,225 m, 08.xii.2014, Al Dhafer et al., 1w); Shada Al A’la Mountain (19.851, 41.301, 1,325 m, 15.ii.2014, Al Dhafer et al., 1w); Shada Al A’la Mountain (19.839, 41.310, 15.xi.2015, Al Dhafer et al., 3w: KSMA).

Other Material. Jazan Province: Zabia (17.107, 42.650, 43 m, 09.iv.2012, M. R Sharaf, MRS0070, 2w); Abu Arish (17.013, 42.802, 90 m, 10.iv.2012, M. R Sharaf, MRS0073, 10w); Jazan (16.97627, 42.61743, 38 m, 12.iv.2012, M. R Sharaf, MRS0077, 25w: KSMA, 1w: CASC, 1w: BMNH, 1w: WML, 1w: OXUM, 1w: LACM).

Measurements. Holotype: TL 2.01; HL 0.49; HW 0.39; SL 0.42; EL 0.12; EM 0.07; ML 0.59; PW 0.25; PTL 0.11; PTW 0.11; PPL 0.09; PPW 0.09; CI 80; EI 31; SI 108.

Paratype workers: TL 1.50–2.55; HL 0.42–0.49; HW 0.32–0.39; SL 0.28–0.42; EL 0.07–0.12; EM 0.07–0.09; ML 0.45–0.59; PW 0.21–0.31; PTL 0.09–0.14; PTW 0.07–0.11; PPL 0.07–0.09; PPW 0.07–0.09; CI [69–86]; EI 21–31; SI 80–108 (n = 13).

Diagnosis. Monomorium heggyi is diagnosed by the following character combination: scapes when laid back from their insertions just reaching posterior margin of head; head in full-face view with eyes located nearly at midlength; promesonotal outline feebly convex or flat, sloping posteriorly to narrow and shallowly impressed metanotal groove.

Worker. Head. Head in full-face view distinctly longer than broad, with concave posterior margin and shallowly convex sides and feebly concave posterior margin; median portion of clypeus with anterior free margin slightly indented; eyes of moderate size, in profile with convex dorsal sides and straight ventral side, maximum diameter 0.21 x– 0.30 x HW, with 7 ommatidia in longest row; head in full-face view eyes located nearly at midlength of head and just breaking sides; scapes when laid back from their insertions just reaching posterior head margin. Mesosoma. Promesonotal outline feebly convex or flat, slopping posteriorly to narrow and shallowly impressed metanotal groove; propodeal dorsum in profile convex making a continuous curve with propodeal declivity and with defined lateral margins. Petiole. Petiole with high rounded node in profile; subpetiolar process broad and blunt. Postpetiole. Postpetiolar node lower than petiolar node in profile and nearly as broad as petiole in dorsal view. Sculpture. Mandibles feebly longitudinally sculptured; cephalic surface with faint vestiges of superficial reticular patterning, almost entirely effaced, area between frontal carinae finely longitudinally striate; clypeus smooth; entire mesosoma, petiole and postpetiole sharply and densely reticulate-punctate; gastral tergites smooth and shining. Pilosity. Dorsum of head without standing hairs behind the level of the frontal lobes; several pairs of long hairs on the anterior clypeal margin and on mandibles; antennae with dense appressed pubescence; mesosoma, petiole and postpetiole without standing hairs of any description; first gastral tergite without standing hairs except for sparse appressed pubescence; pilosity of remaining gastral tergites restricted to the posterior margins. Color. Uniformly yellow.

Remarks. Monomorium heggyi belongs to the M. salomonis species-group (Bolton, 1987). It is most similar to M. rabirium Bolton, 1987 from Botswana from which it is readily distinguished by the longer scapes (SI 80–108) that reach the posterior head margin in full-face view, the posteriorly shifted eyes located nearly at the midlength of head in full-face view. Monomorium rabirium has shorter scapes (SI 92–97) that fail reaching the posterior head margin in full-face view, and eyes conspicuously located in front of midlength of head in full-face view. Among the Arabian species of the M. salomonis species-group, M. heggyi is superficially similar to M. elghazalyi from the Socotra Archipelago from which it can be easily separated by the larger eyes (EI 21–31), the shallowly impressed metanotal groove, and the densely sculptured mesosoma, petiole and postpetiole. Monomorium elghazalyi has smaller eyes (EI 19–20), broadly and deeply impressed metanotal groove, and a smooth body surface.

Etymology. The patronymic name honors Dr. Essam Heggy, the Egyptian space scientist at NASA.

Habitat. The type locality, Shada Al A’la, is a Nature Reserve (Fig. 17) located in the Al Bahah Province in the southwestern KSA at an elevational range of 470–2,222 m. The locality is characterized by relatively high rainfall, diverse habitats, and high biodiversity, as well as by the presence of large areas of terraced fields used for cultivating banana, coffee, figs, and lemon. The region has a diverse range of wild vegetation cover including plants of the Leguminosae (Fabaceae), composites (Asteraceae), and graminoides (Poaceae). Acacia (Fabaceae) and Juniper (Cupressaceae) are the most dominant plants (SWA, 2018; El-Hawagry et al., 2016). Shada Al-A’Ala harbors a high number of endemic animals including birds, mammals (SWA, 2018) and insects (El-Hawagry et al., 2016).

Geographic Distribution. KSA.

Monomorium khalidi Sharaf, sp. n.

(Figs. 18A–18C)

Holotype pinned worker. KSA: Al Bahah Province: Shada Al A’la (19.839, 41.310, 1,563 m, 18.x.2014, Al Dhafer et al., CASENT0922288, KSMA).

Three paratype, pinned workers, KSA: Jazan Province: Wadi Shahdan (17.452, 42.715, 200 m, 13.xi.2012, M.R. Sharaf, MRS0131, CASENT0919810, KSMA); Fayfa, Wadi Al Jora (17.279, 43.062, 419 m, 06.iv.2013, M.R. Sharaf, KSMA).

Measurements. Holotype: TL 3.16; HL 0.75; HW 0.67; SL 0.62; EL 0.14; EM 0.25; ML 0.95; PW 0.44; PTL 0.27; PTW 0.21; PPL 0.17; PPW 0.21; CI 89; EI 21; SI 93.

Paratype workers: TL 2.31–2.98; HL 0.59–0.72; HW 0.49–0.59; SL 0.45–0.59; EL 0.14–0.15; EM 0.11–0.18; ML 0.71–0.85; PW 0.32–0.41; PTL 0.28–0.32; PTW 0.11–0.15; PPL 0.11–0.17; PPW 0.08–0.15; CI 81–83; EI 24–29; SI 92–102 (n = 3).

Diagnosis. Monomorium khalidi can be distinguished by the combination of the following characters: short scape failing to reach posterior head margin in full-face view; abundant mesosomal pilosity; straight outline of promesonotum; densely reticulate-punctate surfaces of head, mesosoma, petiole, and postpetiole; promesonotum dorsally with at least five to six pair of hairs, promesonotum and propodeum each with three pairs.

Worker. Head. Head nearly as long as broad, or little longer than broad with concave posterior margin and feebly convex sides; median portion of clypeus with anterior free margin distinctly concave; eyes of moderate size, in profile view with convex dorsal sides and straight ventral side, maximum diameter 0.20 × HW, with 9–10 ommatidia in longest row); head in full-face view with eyes failing to break head sides; scapes when laid back from their insertions failing to reach posterior margin. Mesosoma. Promesonotal outline flat, slopping posteriorly to narrow and feebly impressed metanotal groove; propodeal dorsum flat and short, longitudinally concave, with sharply defined lateral margins. Petiole. Petiole with high rounded node in profile. Postpetiole. Postpetiole as broad as petiole in dorsal view. Sculpture. Cephalic surface between and immediately behind frontal lobes finely longitudinally striate; cephalic surface and sides, entire mesosoma, petiole and postpetiole sharply and densely reticulate-punctate; first gastral tergite shagreened and relatively shining. Pilosity. Cephalic surface with several pairs of standing hairs behind level of frontal lobes; posterior margin of head with three pairs of standing hairs; underside of head with about five pairs of short hairs; promesonotum dorsally with at least five to six pair of hairs, promesonotum and propodeum each with three pairs; petiole and postpetiole each with two-three pairs of backward directed hairs; first gastral tergite with numerous standing hairs which are evenly distributed over the sclerite in front of the apical transverse row. Color. Bicolored species, head, mesosoma, petiole, postpetiole and appendage light red brown, gaster black.

Remarks. This new species is a member of the M. salomonis species-group (Bolton, 1987). Monomorium khalidi is closest to M. junodi Forel, 1910 from South Africa in terms of the relatively small eyes, the short scapes that fail to reach posterior margin of head, the acute metanotal groove, and densely punctate body surface. The two species have short scapes that fail to reach posterior margin of head in full-face view, metanotal groove feebly impressed; body surface densely punctate; and propodeal longitudinally concave, with sharply defined lateral margins. However, M. khalidi can be easily distinguished from M. junodi by the following characters: body bicolored with head, mesosoma, petiole, postpetiole and appendages light red-brown contrasting with the black gaster; head in full-face view with eyes failing to break sides; promesonotum dorsally with at least five to six pair of hairs, promesonotum and propodeum each with three pairs; promesonotal outline flat. Monomorium junodi is uniformly brown to dark brown, head in full-face view with eyes breaking sides; promesonotum dorsally with two pair of hairs, propodeum without hairs; promesonotal outline feebly but distinctly convex. Among the Arabian Monomorium species, M. khalidi is superficially similar to M. nitidiventre in terms of body size, surface sculpture, eye shape but the former can be readily recognized by the reduced stiff pilosity.

Etymology. The patronymic name honors Khalid Amr (born at 04/11/2012), the son of the second author.

Habitat. The type locality of M. khalidi is Shada Al A’la (Fig. 19), the same locality where M. heggyi was collected.

Geographic Distribution. KSA.

Monomorium niloticum Emery, 1881

(Figs. 20A–20C)

Monomorium niloticum Emery, 1881: 533 (w.) Egypt. Palearctic. [MSNG], [Syntype worker, CASENT0905755, image examined].

Combination in Monomorium (Xeromyrmex): Emery, 1922: 179; subspecies of Monomorium venustum: Forel, 1910: 6; Wheeler & Mann, 1916: 170; Stitz, 1917: 346; Finzi, 1936: 175; revived status as species: Santschi, 1936: 37; see also: Collingwood & Agosti, 1996: 352; current subspecies: nominal plus M. n. gracilicorne, M. n. niloticoides.

Senior synonym of Monomorium matame Collingwood & Agosti, 1996: 350, fig. 22 (w.) OMAN. Palearctic, Holotype worker, Oman, Wadi Matam (0l.II.1986, M.D. Gallagher, CASENT0922325, WML) [examined] syn. n.

Material examined. KSA: Asir Province: Jebel Al Habala (18.038, 42.873, W. Buttiker, 1w); Alkhola (13.600, 44.283, 4w, WML). Al Baha Province: Al Atawla, Al Baha-Taif RD, Wadi Bawa (20.750, 41.247, 1,310 m, 08.xi.2012, M.R. Sharaf, MRS0099, 7w, 1w: CASENT0906397); Wadi Elzaraeb (20.073, 41.387, 2,086 m, 09.v.2011, M.R. Sharaf, 3w); Al Mandaq, Wadi Turabah (20.242, 41.263, 1,715 m, 19.ix.2011, M.R. Sharaf, 6w); Hawtat Bani Tamim (23.525, 46.845, 19.iv.2008, M.R. Sharaf, 6w); Riyadh city (06.viii.2008, 1w); Wadi Hanifa (24.671, 46.595, 641 m, 11.iv.2013, M.R. Sharaf, 11w); Al Mandaq, Wadi Turabah (20.211, 41.288, 1,793 m, 10.v.2011, M.R. Sharaf, 4w). Riyadh Province: Al Hayer (24.280, 46.766, 647 m, 10.iii.2011, A.S. Aldawood, 24w); Al Hayer (24.557, 46.744, 589 m, 11.iv.2014, S. Salman, 5w); Dawademi (24.557, 44.377, 983 m, 18.iv.2014, S. Salman, 6w); Dawademi (24.478, 44.364, 1,027 m, 18.iv.2014, S. Salman, 4w); Dawademi (24.583, 44.323, 966 m, 16.i.2015, S. Salman, 9w); Dawademi (24.538, 44.355, 999 m, 16.i.2015, S. Salman, 1w); Afif (23.900, 42.881, 1,052 m, 17.i.2015, 1w); Afif (23.957, 42.976, 1,059 m, 17.i.2015, S. Salman, 6w); Dhurma (24.607, 46.130, 646 m, 30.i.2015, S. Salman, 8w); Hawtat Bani Tamim (23.454, 46.819, 582 m, 19.ii.2015, M.R. Sharaf, 3w); Hawtat Bani Tamim (23.500, 46.850, 612 m, 19.ii.2015, M.R. Sharaf, 2w); Hareeq (23.614, 46.054, 689 m, 22.ii.2015, S. Salman, 29w); Quwayia (24.070, 45.280, 823 m, 03.v.2014, S. Salman, 3w); Majma’a (26.005, 45.019, 730 m, 13.ix.2014, S. Salman, 6w, KSMA); Riyadh (23.953, 43.636, x.1979, W. Buttiker, 2w); Wadi Eflah, x.1983, W. Buttiker, 2w); wadi Mawran (22.050833, 46.671944, 10.ii.1985, W. Buttiker, 6w); Riyadh (24.7136, 46.6753, 07.vii.1975, W. Buttiker, 1w); Shoiba (Shuaibah) (20.6295, 39.5624, 06.xii.1983, W. Buttiker, 2w); Wadi Nimar (24.5705, 46.68, v.1983, W. Buttiker, 2w); Harithi (21.28, 40.28, 11.v.1984, W. Buttiker, 1w); Wadi Ellah (09.ix.1986, W. Buttiker, 3w, WML); Malham (25.154, 46.282, 711 m, 15.ix.2014, S. Salman, 4w); Malham (25.161, 46.229, 742 m, 15.ix.2014, S. Salman, 1w); Quwayia (24.058, 45.245, 846 m, 29.x.2014, S. Salman, 4w); Quwayia (24.05043, 45.25795, 839 m, 29.x.2014, S. Salman, 12w); Quwayia (24.053, 45.262, 836 m, 29.xi.2014, S. Salman, 2w); Na’jan (24.026, 47.138, 467 m, 13.xii.2014, S. Salman, 9w); Wadi Al Dawaser (22.778, 44.786, 686 m, 20.ii.2015, S. Salman, 3w); Wadi Al Dawaser (20.778, 44.786, 686 m, 20.ii.2015, S. Salman, 3w); Qassim, Buraydah (26.216, 44.0414, 633 m, 17.ix.2011, Steyaningrum, 9w); Qassim, Buraydah (26.330, 43.979, 623 m, 19.x.2013, M.R. Sharaf, 9w); Huraymila (25.1487, 45.950, 815 m, 07.ii.2011, M.R. Sharaf, 9w); Dirab Research Station (24.419, 46.654, 570 m, 28.ix.2011, B.L. Fisher, 1w, CASENT0260164; Dirab Research Station (24.737, 46.618, 662 m, 29.ii.2012, K. Mahmoud, 27w); Naam Dam (23.628, 46.631, 646 m, 22.ii.2015, S. Salman, 30w); Dirab (24.409, 46.662, 588 m, 30.xii.2009, M.R. Sharaf, 6w); Salboukh (25.079, 46.347, 689 m, 05.xi.2009, M.R. Sharaf, 15w); Salboukh (25.074, 46.377, 728 m, 26.xi.2014, S. Salman, 12w); Ghiyanah (25.074, 46.226, 728 m, 26.xii.2014, S. Salman, 3w); Al Hayer (24.280, 46.766, 10.iii.2011, A.S. Aldawood, 10w); Qassim, Buraydah (26.338, 44.024, 643 m, 19.x.2013, S. Salman, 2w); Wadi Al Dawaser (20.487, 44.764, 690 m, 22.i.2014, S. Salman, 1w, All previous material in KSMA); Wadi Khumra (17.viii.1979, W. Buttiker, CASENT0249836, 1w, NHMB). Mekkah Province: Ras Hatibah (21.978, 38.937, 11.i.1983, 2w, WML). OMAN: Nakhl (23.44696, 57.88062, 364 m, 02.iv.2016, M.R. Sharaf, 8w, CASENT0922306); Dhofar, Dhalkout (16.727, 53.249, 623 m, 18.xi.2017, M.R. Sharaf, 6w, CASENT0922859, KSMA); no locality (2005, 1w); no locality (xi.1984, 1w); Jebel Akhdar (23.073, 54.662, 1w); Wattayah (23.591, 58.363, 1983, 3w, WML). UNITED ARAB EMIRATES: Wadi Maidaq (25.300, 56.117, 22.xi-02.xii.2010, M. Hauser et al., UAE12977, 1w, CASENT0264568, KSMA); Hatta (24.806, 56.125, iii.1998, A.V. Harten, 2w); Hatta (24.806, 56.125, iii.1995, A.V. Harten, 2w, WML). YEMEN: Ta’iz (13.578, 44.018, A.V. Harten, 1w); Al Kawd (13.089, 45.365, 1991, A.V. Harten, 2w, WML).

Remarks. Monomorium matame was described from Oman and KSA based on the worker caste. In the original description Collingwood & Agosti (1996) pointed out the similarity between M. matame and M. niloticum and used variable characters that were not useful in species recognition. Our examination of the type material of both shows that M. matame is not separable from M. niloticum. The two species share the following characters: scapes when laid back from their insertions failing to reach posterior head margin; eyes relatively large about 0.30–0.33 × HW; metanotal groove deeply impressed; mesosoma with several pairs of scattered standing hairs; promesonotum with three pairs, mesonotum with two to three pairs, propodeum with a single pair of hairs; bicolored species with head, mesosoma, petiole, postpetiole red-brown contrasting with dark brown to black gaster. Based on the examination of the type images of both species, we propose to synonymize M. matame as a junior synonym of M. niloticum, on the basis of morphological similarity.

Geographic Distribution. Monomorium niloticum is originally described from Egypt and widely spread in the Arabian Peninsula (Collingwood, 1985; Collingwood & Agosti, 1996; Collingwood et al., 2011, Sharaf et al., 2018b). It is also collected from Israel (Vonshak & Ionescu-Hirsch, 2009), and North Africa (Sharaf, 2006; Borowiec, 2014). Monomorium niloticum is one of the most broadly spread myrmicine species throughout several countries of the Arabian Peninsula including the KSA, Oman, UAE, and Yemen (Collingwood, 1985; Collingwood & Agosti, 1996).

Ecological and Biological notes. The broad geographic distribution of the species can be interpreted in the light of the species diverse habitat preferences, including the deserts, mountainous, and cultivated sites. Several worker series were found nesting in either dry or humid soil beneath rocks in an undisturbed site in the KSA where a broad diverse of plant species exists including Acacia (Fabaceae), Citrus limon (L.) Osbeck (Rutaceae), Prunus dulcis (Mill.) D. A. Webb (Rosaceae), Juniperus L. (Cupressaceae), Mangifera indica L. (Anacardiaceae), Ficus sp. (Moraceae), Hibiscus L. (Malvaceae) and Azadirachta indica A. Juss. (Meliaceae).

Monomorium nitidiventre Emery, 1893

(Figs. 21A–21C)

Monomorium bicolor subsp. nitidiventris Emery, 1893: 256 (w.) Egypt. Palearctic. [MSNG], [Syntype worker, CASENT0904602, image examined].

Mayr, 1901: 7 (q.); Karavaiev, 1911: 5 (m.); combination in Monomorium (Xeromyrmex): Wheeler, 1922: 869; subspecies of Monomorium bicolor: Santschi, 1938: 39; of Monomorium subopacum: Santschi, 1927: 245; Menozzi, 1932: 94; Bernard, 1953: 159; Hamann & Klemm, 1967: 413; raised to species: Collingwood, 1985: 272; see also: Wheeler & Mann, 1916: 171; Collingwood & Agosti, 1996: 352.

Monomorium yemene Collingwood & Agosti, 1996: 357, fig. 32 (w.) Yemen. Afrotropic. Holotype worker, Yemen, Taiz (20.x.1991, A. van Harten, NHMB) [Presumed lost]; Paratype worker, Yemen, Zingibar- Shuqrah (13.356, 45.700, 21.iii.1993, C.A. Collingwood, CASENT0913865, NHMB) [examined] syn. n.

Material examined. YEMEN, W. Adem Port, Wadi Tiban, N. W. of Jebel Jihaf (13.198, 44.787, ~1,158 m, 22.x.1937, C.A. Collingwood, from flower of Adenium sp., B. M. Exp. To S. W. Arabia, H. Scott & E. B. Britton, B. M. 1938-246, BMNH (E) 1017382, 1w, CASENT0914158, BMNH).

Remarks. The synonymy of M. yemene with M. nitidiventre is straightforward since both are morphologically similar and indistinguishable. Both share the following key characters: posterior margin emarginated in full-face view; median portion of anterior clypeal margin distinctly concave; metanotal groove deeply impressed; head, mesosoma, petiole, and postpetiole densely reticulate-punctate and covered with abundant pale standing hairs.

Note: However, the locality label of the paratype specimen (CASENT0913865) (Madinat Al shiraq) is not matching the locality data mentioned in the original description but the collecting data and collector are congruous with the description, therefore, this specimen is treated as one of the type material of M. yemene.

Geographic Distribution. Monomorium nitidiventre is originally described from Egypt and recorded from the KSA, Kuwait and Yemen (Collingwood, 1985; Collingwood & Agosti, 1996).

Monomorium subdenticorne Collingwood & Agosti, 1996

(Figs. 22A–22C)

Monomorium subdenticorne Collingwood & Agosti, 1996: 354, fig. 27 (w.) Yemen. Afrotropic.

Material examined. KSA: Asir Province: Ahad Refedah (18.134, 43.001, 2,179 m, 23.ii.2015, M. Alharbi, 2w, KSMA). Yemen: Ghaiman, about 9 miles S. E. of San’a (13.933, 44.833, ~8,400 ft, 18.ii.1938, B. M. Exp. To S. W. Arabia, H. Scott & E. B. Britton, B. M. 1938-246, BMNH1017456, 1w, CASENT0914318, BMNH).

Geographic Distribution. A species originally known from Yemen and herein collected for the first time from the KSA.

Monomorium venustum (Smith, 1858)

(Figs. 23A–23C)

Myrmica venusta Smith, 1858: 126 (w.) Syria. Palearctic.

Material examined. KSA: Asir Province: Wadi Asidah (20.417, 41.200, 10.ix.1983, 1,480 m, W. Buttiker, 1w, WML). Riyadh Province: Zulfi (26.272, 44.771, 635 m, 18.i.2014, S. Salman, 15w); Mezahmyia (24.466, 46.251, 648 m, 29.xi.2014, S. Salman, 10w); Dawademi (24.552, 43.932, 873 m, 16.i.2015, S. Salman, 1w); Bijadriyah (24.310, 43.731, 439 m, S. Salman, 2w); Afif (23.900, 42.081, 1,052 m, 17.i.2015, S. Salman, 18w); Shaqra (25.270, 45.291, 712 m, 23.i.2015, 63w); Sajir (25.165, 44.601, 750 m, 23.i.2015, S. Salman, 6w); Shaqra (25.274, 45.300, 707 m, 24.i.2015, S. Salman, 2w, KSMA). Kuwait: Kuwait (no date, 2w, WML). Oman: Wahiba sands (21.438, 58.554, 23.iii.1986, W. Buttiker, 1w, WML). United Arab Emirates: Jebel Hafit (24.050, 55.767, 27.ii-03.iii.2011, M. Hauser et al., UAE13010, 1w, CASENT0264463); Um Al-Quwain (12. iv-07.vi.2009, M. Hauser et al., UAE12920, 1w, CASENT0264584); Ar-Rafah (25.717, 55.867, 15-30. x.2010, M. Hauser et al., UAE12866, CASENT0264475, KSMA); Wadi Asidah (20.417, 41.200, 10.ix.1983, W. Buttiker, 1w); Riyadh (24.714, 46.675, 18.ii.1975, W. Buttiker, 1w); Sharjah (25.346, 55.421, vii.2003, A.V. Harten, 2w, WML). Yemen: Sana’a (15.369, 44.191, iii.1990, 1w, WML).

Geographic Distribution. Monomorium venustum is originally described from Syria and recorded from the KSA, Kuwait, Oman (Collingwood, 1985; Collingwood & Agosti, 1996; Sharaf et al., 2018b), Israel (Vonshak & Ionescu-Hirsch, 2009), and North Africa (Borowiec, 2014).

Biogeographical analysis

Twenty-four species are Arabian endemics. Afrotropical (5) and Palearctic (12) species were also identified (Table 1; Figs. 24–29).