Ectomomyrmex horni

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Ectomomyrmex horni
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Ponerinae
Tribe: Ponerini
Genus: Ectomomyrmex
Species: E. horni
Binomial name
Ectomomyrmex horni
(Forel, 1913)


Common Name
Minamifuto-hariari
Language: Japanese

In Japan, Ectomomyrmex horni inhabits sparse forests and forest edges. Workers are often found under stones but nests are constructed in soil with complicated systems of passages and chambers (Yamane et al., 2024).


Photo Gallery

  • Yamane et al. (2024), Fig. 3. Habitus (queen) in profile view. A – Cryptopone sauteri (Wheeler, 1906) (Aman-dake, Hirado-jima, Nagasaki-ken, Kyushu, 7.ix.1982, K. Ogata & S. Eto leg.); B – Diacamma cf. indicum Santschi, 1920 (gamergate) (Ishimine, Naha-shi, Okinawa-jima, Okinawa Is., Okinawa-ken, 24.iv.1979, K. Ogata leg.); C – Ectomomyrmex horni (Forel, 1913) (Campus of Kagoshima Univ., Kagoshima-shi, Kagoshima-ken, Kyushu, 21.ix.1992, Sk. Yamane leg.); D – Parvaponera darwinii (Forel, 1893) (Yui-dake, Amami-ôshima, Amami Is., Kagoshima-ken, 26.vii.2019, Sk. Yamane leg.); E – Ponera kohmoku Terayama, 1996 (Shiroyama, Kagoshima-shi, Kagoshima-ken, Kyushu, 24.x.1978, K. Ogata leg.).
  • Yamane et al. (2024), Fig. 5. Habitus (queen) in dorsal view. A – Cryptopone sauteri (Wheeler, 1906); B – Diacamma cf. indicum Santschi, 1920 (gamergate); C – Ectomomyrmex horni (Forel, 1913); D – Parvaponera darwinii (Forel, 1893); E – Ponera kohmoku Terayama, 1996. (Collection data same as in fig. 3).
  • Yamane et al. (2024), Fig. 7. Head (queen) in full-face view. A – Cryptopone sauteri (Wheeler, 1906); B – Diacamma cf. indicum Santschi, 1920 (gamergate); C – Ectomomyrmex horni (Forel, 1913); D – Parvaponera darwinii (Forel, 1893); E – Ponera kohmoku Terayama, 1996. (Collection data same as in fig. 3).
  • Yamane et al. (2024), Fig. 8. Ectomomyrmex horni (Forel, 1913). A–C – worker (Sata-misaki, Minamiôsumi-chô, Kagoshima-ken, Kyushu, 7.v.2022, Sk. Yamane leg., JP22-SKY-019); D–F – male (Campus of Kagoshima Univ., Kagoshima-shi, Kagoshima-ken, Kyushu, 20.ix.1999, collector unknown). For the queen see figs 3C, 5C & 7C.

Identification

The identity of this taxon is currently unsettled. Yamane et al. (2024) provide the following notes:

Ectomomyrmex horni was described by Forel (1913) as a species of Pachycondyla closely related to Ectomomyrmex sauteri based on the worker and queen castes. Forel (1913) mentioned that in the worker this species is separated from the latter mainly by a larger body (7.0–7.5 mm; 6.5 mm in E. sauteri) and the anteroventral corner of the pronotum bluntly angulate (produced as a tooth in E. sauteri). Another related species, Ectomomyrmex denticeps, was described by Wheeler (1929); this is very peculiar in having a distinct tooth at the posterolateral corner of the head (Wheeler 1929: 33, fig. 2). However, Yasumatsu (1962) mentioned that another specimen in the MCZ (not cited by Wheeler) displays a different condition of this character, suggesting that the holotype shows an anomaly. Yasumatsu (1962) assigned all the above forms to Ectomomyrmex, synonymized E. horni and E. denticeps with Ectomomyrmex javanus, and suspected that E. sauteri is also a junior synonym of E. javanus (type locality: Java). Although Onoyama (1980) considered E. horni to be conspecific with E. sauteri, Bolton (1995) treated them as different species with the former being a junior synonym of E. javanus (referred to as Pachycondyla javana). In the material from Taiwan and Japan (except for Tsushima) examined by us the body size is more similar to that of E. horni, though rather variable, and the anteroventral corner of the pronotum is roundly angulate as in E. horni. These specimens agreed well with the original description and the images of the syntype of E. horni on AntWeb (2024). We have thus concluded that the material we examined belonged to E. horni. Terayama (2020: 90) tentatively treated the Japanese population as Ectomomyrmex sp. B, but inferred that it is most probably E. horni, reaching a conclusion similar to our view. At present it is not certain if E. sauteri and E. horni are conspecific or not as the available material of this species complex is still insufficient.

Apart from the status of Ectomomyrmex sauteri and E. denticepes, E. horni is clearly separated from E. javanus by the following combination of worker characteristics:

  1. body small with head width 1.56–1.73 mm (2.03–2.23 mm in E. javanus)
  2. dorsum of head very densely and finely rugulose or punctorugulose; rugulae more or less regular, but frequently branching or reticulate (rugulae sharply defined and coarser, more constantly regular in E. javanus)
  3. lateral face of head weakly punctate-rugulose, matte (more coarsely rugulose in E. javanus)
  4. frontal lobe laterally with distinct smooth area (smooth area lacking or much less distinct in E. javanus)
  5. mandible generally with scattered punctures in basal half and well defined longitudinal striae in apical half, but essentially shiny (mandible opaque even if entirely without visible sculpture; striation, if any, microscopic in E. javanus)
  6. eye with sparse but conspicuous erect hairs (essentially without erect hairs in E. javanus)
  7. outer face of mid- and hindtibiae without erect hairs (with many erect hairs in E. javanus)

Two worker specimens from the Ogasawara Islands have slightly longer antennal scapes (1.54, 1.59 mm) and larger scape indices (SI: 86, 93) compared with workers from the Kyushu mainland and the Ryukyu Islands. More time is needed to entirely resolve the complicated problem surrounding E. horni and E. sauteri.

The Tsushima population of the E. javanus-complex (= Ectomomyrmex japonicus and Ectomomyrmex sp. A of Terayama et al. 2014) is more similar to the Korean and some other continental populations in having mandibles that are entirely striate and matte. The workers of these populations are constantly larger than those of E. horni, and the dorsum of the head has more regular rugae. Larger forms from Southeast Asia generally lack erect hairs on the eye, while in other characters they have various combinations of character conditions. DNA information is prerequisite for correct sorting of samples of this complex (currently assigned to E. javanus or treated as different species) from entire Asia into species.

Distribution

Distribution based on Regional Taxon Lists

Oriental Region: China, Japan, Taiwan (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.
pChart

Biology

Castes

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • horni. Pachycondyla (Ectomomyrmex) horni Forel, 1913f: 185 (w.q.) TAIWAN.
    • Type-material: syntype workers, syntype queen(s) (numbers not stated).
    • Type-localities: Taiwan (“Formosa”): Akau, Taihorinsho, Suisharyo, and Hoozan (H. Sauter).
    • Type-depositories: DEIB, MHNG, MHNU.
    • Combination in Ectomomyrmex: Santschi, 1925f: 82.
    • [Note: Ectomomyrmex is rendered in error as Ectatomma by Santschi, 1937h: 363.]
    • Junior synonym of javanus: Yasumatsu, 1962: 94; Bolton, 1995b: 306; Imai, et al. 2003: 212.
    • Synonym of sauteri: Onoyama, 1980: 196; Terayama, 2009: 104.
    • [Note: if synonymy correct then sauteri has priority. It is suspected that javanus is the senior synonym of both sauteri and horni.]
    • Status as species: Santschi, 1925f: 82; Wheeler, W.M. 1929f: 1; Wheeler, W.M. 1929g: 58; Wheeler, W.M. 1930h: 59; Santschi, 1937h: 363; Chapman & Capco, 1951: 61; Terayama, 2009: 104; Yamane et al., 2024: 263.
    • Senior synonym of denticeps: Terayama, 2009: 104.
    • Distribution: China, Japan, Taiwan.

Description

References

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