Monomorium minimum subsp. compressum Wheeler, 1904

Seifert, Bernhard, 2025, The Monomorium carbonarium species group in the Nearctic and Europe (Hymenoptera: Formicidae), Soil Organisms (Toronto, Ont.) 97 (1), pp. 55-84 : 73-75

Monomorium minimum subsp. compressum Wheeler

1904 [type investigation]

This taxon has been described from the state of Hidalgo, Mexico based on “ four females and several workers taken at San Miguel beneath a stone” ( Wheeler 1914). Investigated were a paratype wingless gyne and four paratype workers from the holotype nest labelled “San Miguel. Hidalgo, Mexico W. M. Mann ” and “WM Mann 1954 Collection”; depository NMNH Washington. The status of a different species was maintained here due to the very different gyne ( Tab. 5, Figs. 6, 27 , 28). The workers are in nearly all characters fully within the range of Monomorium ergatogyna or M. carbonarium ( Tab. 3) but are possibly separable by multivariate analyses (see below). It is puzzling how DuBois could determine in the NMNH Washington collection worker samples from four other localities in Mexico as M. compressum since the differential characters stated in his key are useless All material examined. Only the holotype nest sample and another one with four workers were available for investigation .

Geographic range. Only the holotype sample from locality San Miguel in the Mexican state of Hidalgo and the sample of four investigated workers from Mexico (city?) was available .

Description: - -Worker ( Tab. 3, key). Most similar to M. carbonarium and M. ergatogyna with almost no morphometric character being outside the range of variation of that species. The differential characters supposed below have to be checked in a larger sample. Very small, CS 453 ±19 µm. Head more elongated than in M. carbonarium and M.ergatogyna,CL /CW1.247 ±0.008.Dents on clypeal marginshorterthanin M.carbonarium and M. ergatogyna (ExCly/CS 3.04 ± 0.47%), not very acute and moderately distant (ClSpD/CS 10.12 ± 0.90%). Frontal carinae moderately distant and very slightly diverging frontad (FL/CS 0.270 ± 0.007, FR/CS 0.266 ± 0.003, FL/FR 1.017 ± 0.012). Eye and preocular distance moderately large (EL/CS 0.206 ± 0.004, PrOc/CS 0.227 ±0.005). Scape and funiculus segments moderately long (SL/CS 0.812 ± 0.009, Fu2/CS 6.13 ± 0.39%, Fu3/CS 4.96 ± 0.32%). Mesosoma longer than in M. carbonarium and M. ergatogyna and moderately wide (ML/CS 1.207 ± 0.018, MW/CS 0.561 ± 0.016). Metanotal groove rather shallow, MGr/CS 4.29 ± 0.55%. Dorsum and slope of propodeum in profile forming a convex curve or a suggested very blunt angle. Petiole moderately wide, high and long (PeW/CS 0.260 ± 0.017, PeH/ CS 0.358 ± 0.008, PeL/CS 0.428 ±0.011). Postpetiole rather wide and moderately high (PpW/CS 0.316 ± 0.021, PpH/CS 0.276 ±0.012). All body surfaces with exception of suggested rugulae on lateral frontal lobes, genae and ventrolateral area of metapleuron glabrous and shiny. Head, mesosoma, waist and appendages brown, gaster blackish brown.

--Gyne ( Tab. 5, Figs. 27 , 28): The morphometric data and images reveal a unique gyne morphology.

Taxonomic comments. The unique gyne morphology should justify the status as a good species but worker identification is most difficult. In an attempt to separate the Nearctic triple Monomorium carbonarium , M. ergatogyna and M. compressum , it was possible to isolate the two samples of M. compressum by a PCA using the 13 characters FR/CS, PeH/CS, ExCly/CS, SL/CS, ML/CS, ClSpD/CS, MGr/CS, CL/CW, PpW/CS, PpH/CS, FL/FR, PeW/CS, EL/CS ( Fig. 35). I consider this result as provisional.

Biology. Nothing is known except for polygynous colony demography.

Monomorium gallicum n.sp.

Etymology: belonging to Gallia, a province of the Roman Empire largely coincident with modern France and the area where most findings of the new species were made.

Type material. Holotype worker labelled “ FRA: 47.16846, 0.25379, 75 m, Chapelle Sainte Radegonde, swarming, Gouraud 2021.07.10 -4”, “ Holotype Monomorium gallicum Seifert ”; 5 worker paratypes and 2 wingless gyne paratypes on two separate pins from the holotype nest with same collecting data but “ Paratypes Monomorium gallicum Seifert ”; all this material deposited in SMN Görlitz.

All material examined. Morphometrically investigated were 23 nest samples with 73 workers and 10 gynes. They came from France (21 samples) and Germany (2 samples). For details see supplementary information SI1, SI2, SI3. Geographic range and supposed origin. The vouchers from France concentrate to a zone of some 70000 km ² in SW France influenced by Atlantic climate from sea level to 168 m, with border points Ile-d’Yeu in the northwest (46.69°N, 2.28°W), Chapelle Sainte Radegonde in the northeast (47.17°N, 0.25°E), La Roque-Gageac in the east (44.83°N, 1.19°E] and Samatan in the south (43.49°N, 0.93°E). The two introduced supercolonial populations in urban regions around Mannheim in SW Germany are 42 km apart. The species was not found in the investigat- ed Nearctic material and should be of European or at least Old World origin. Assuming an autochthonous European origin appears somewhat problematic. Bernard (1968) described the presence of an ant that he called Monomorium minutum Mayr 1855 for West Europe and the whole Mediterranean. Unable to separate Monomorium monomorium , M. carbonarium and M. gallicum n.sp., it appears likely that he collected two or three species under this name. However, it is strange that he did not report any observation suggesting supercoloniality. Supercolonies should also not have escaped the attention of other 20th century myrmecologists such as C. Collingwood but there are no reports for this. Monomorium gallicum n.sp. was either not present in Europe in that time or its colonies remained unobtrusive for most of their evolutionary history and developed a supercolonial demography only recently. The latter idea is not far-fetched as very recent occurrence of supercolonies in urban environments is documented for example in Plagiolepis pygmaea (Latreille 1798) from France ( Charrier et al. 2020) as well as Switzerland and Germany in 2019 and 2021 (my own unpublished data).

Diagnosis: --Worker ( Tab. 3; Figs. 23, 24 ; key). Rather small, CS 480 ±18 µm. Head longer than in M. carbonarium, CL /CW 1.242 ± 0.023. Dents on clypeal margin moderately long (ExCly/CS 4.42 ± 0.54%), not very acute and moderately distant (ClSpD/CS 11.48 ±0.79%). Frontal carinae moderately distant and slightly diverging frontad (FL/CS 0.286 ± 0.007, FR/CS 0.276 ± 0.007, FL/FR 1.036 ± 0.020). Eye rather small and preocular distance moderately large (EL/CS 0.199 ± 0.005, PrOc/CS 0.229 ±0.007). Scape and funiculus segments rather long, 3 rd funiculus segment significantly longer than in M. carbonarium (SL/CS 0.824 ± 0.012, Fu2/CS 6.74 ± 0.30%, Fu3/CS 5.35 ± 0.22%). Mesosoma slightly longer than in M. carbonarium and rather narrow (ML/ CS 1.204 ± 0.027, MW/CS 0.571 ± 0.010). Metanotal groove moderately deep, MGr/CS 4.94 ± 0.62%. Dorsum and slope of propodeum in profile forming a convex, suggestedly angulate curve. Petiole rather wide and high but moderately long (PeW/CS 0.293 ± 0.012, PeH/CS 0.380 ± 0.010, PeL/CS 0.438 ±0.014). Postpetiole rather wide and higher than in M. carbonarium (PpW/CS 0.328 ± 0.012, PpH/CS 0.306 ±0.008). All body surfaces with exception of few rugulae on frontal lobes, ventral mesopleuron, ventrolateral area of metapleuron and genae glabrous and shiny. All body parts homogenously dark brown to jet black; mandibles, lateral clypeus and antennal funiculus lighter brown.

--Gyne ( Tab. 5): Only wingless gynes are known so far. Most individuals are morphometrically separable from wingless gynes of M. carbonarium in a PCA ( Fig. 7 ). Perhaps it is also possible to separate them from the latter species by the steeper slope of frontal petiole profile.

Taxonomic comments. The very clear separation of worker samples from M. carbonarium and M. ergatogyna has been demonstrated above ( Figs. 31 , 33; Tab. 1).

Biology. (synthesis of information from C. Gouraud, B. Kaufmann, C. Galkowski, G. Heller pers. comm.). Coastal habitats in France include white and grey dunes, edge of dune groves with maritime pines and holm oaks, cliffs, dry grasslands and road sides. In rural and urban habitats it is found in gardens and parks and once in a greenhouse with Begonia . Occurrence in fully sealed urban habitats such as parking grounds or streets was repeatedly reported and is possible if there is some greenery (trees, flower beds etc.) nearby. Nests are under stones, in dead wood, fence posts and old stone walls. The species is frost resistant: the colony in Weinheim survived the cold winters 2009/2010 and 2011/12. It is very polygynous and may dominate a site where it coexists with Lasius psammophilus , Formica cf. selysi in dune environment and is also able to establish in dune sites colonized by species of the Tapinoma nigerrimum group. Competing ant species are very effectively repelled by gaster-flagging during which an irritating poison gland secretion is released from the extruded sting. Very populous supercolonies were observed in four localities in urban environments. The supercolony in Weinheim became a nuisance in houses and caused damage to electronic installations. On smooth ground the foraging radius may extend more than ten meters. Trophobiotic organisms on bushes and trees such as aphids and scale insects may be visited by huge files of workers. It is extremely polyphagous using nectar and pollen, dead invertebrates, diverse foodstuffs in households and was seen to re- trieve small seeds with elaiosomes. Large arthropods are disintegrated by numerous workers at the site after having repelled competitors. There is one observation of swarming 10 July 2021 from France when the wingless gynes climbed on grasses, branches or other elevated points at the periphery of the nest (SaNo 50). Such behavior makes only sense in order to better attract flying males of other colonies by sex pheromones. This observation corresponds to the case reported above for wingless gynes of Monomorium carbonarium . It remains to be investigated if winged gynes are really absent in this species.

Monomorium ebeninum Forel 1891

Figures

Figure 7. Principal component analysis of wingless gynes of Monomorium carbonarium (black dots), M. ergatogyna (white rhombs) and M. gallicum n.sp. (black crosses). Acronyms indicate the placement of type specimens: W – holotype of M.wheelerorum, C – paratype of M. cyaneum, T – types from holotype nest of M. trageri, G – types from holotype nest of M. gallicum n.sp., E – types from holotype nest of M. ergatogyna.

Figure 24. Lateral aspect of Monomorium carbonarium; Netherlands: Zwartevaal, 2022

Figure 27. Head of Monomorium compressum, paratype wingless gyne; Mexico: Hidalgo: San Miguel

Figure 31. NC-part.hclust analysis of workers of Monomorium carbonarium (black bars), M. ergatogyna (blue bars), and M. gallicum n.sp. (red bars). The empty bar refers to outliers.