Proceratium itoi

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Proceratium itoi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Proceratiinae
Tribe: Proceratiini
Genus: Proceratium
Species: P. itoi
Binomial name
Proceratium itoi
(Forel, 1918)

Proceratium itoi P casent0281853.jpg Proceratium itoi D casent0281853.jpg Specimen Label

A colony of P. itoi collected in Japan by Masuko and collaborators (1985) was formed of 202 workers and 1 queen. Workers are usually collected under stones and within the leaf-litter of glossy-leaved evergreen, deciduous broad-leaved and bamboo forests (Onoyama & Yoshimura 2002).

At a Glance • Larval Hemolymph Feeding  



A member of the Proceratium itoi clade. Differing from the two ingroup species, Proceratium bhutanense and Proceratium malesianum, in the worker, by the palp formula 4,3 instead 3,2 and by the broader frontal carinae, from bhutanense only, by the presence of erect hairs over the whole body, and from malesianum only, by the mid basitarsi with hairs never as much as 1/2 of the mid basitarsal length.

Staab et al. (2018) - Proceratium itoi differs from the other members of the Proceratium itoi clade by the following character combination: medium-sized species (TL 3.46–3.82); sides of head very weakly convex, almost straight, broadest at level of eyes and gently narrowing anteriorly and posteriorly, vertex weakly convex, almost straight; frontal carinae well developed, with large lamellae that extend laterally above the antennal insertions; frontal furrow inconspicuous; posterodorsal corners of propodeum rounded, propodeal declivity superficially punctured (more so dorsally) but largely shiny; posterior face of petiolar node in profile steeper as anterior face; petiole almost as broad as long (DPeI 86–93), apex of petiolar node broader than long in dorsal view; subpetiolar process developed and triangular (but may be small); in addition to dense pubescence abundant erect hairs present on scapes and dorsal surface of body, longest of those hairs shorter than maximum dorsoventral diameter of metafemur.

Proceratium itoi is a typical member of its clade of intermediate size (WL 0.96–1.04) and is similar to most other species in body proportions and indices. Proceratium itoi can be separated from Proceratium williamsi and Proceratium zhaoi by the presence of erect hairs on the dorsal body surface (absent in Proceratium williamsi and Proceratium zhaoi); from Proceratium longmenense by the presence of erect hairs on the scape (absent in Proceratium longmenense) and by the frontal carinae separated at their anteriormost level (touching each other at their anteriormost level in Proceratium longmenense). In Proceratium itoi the posterodorsal corners of propodeum are rounded and this character distinguishes this species from Proceratium bruelheidei and Proceratium kepingmai (posterodorsal corners of the propodeum angular), which are also larger species (WL 1.03–1.10 and 1.14–1.24). The rounded posterodorsal corners of propodeum are shared between Proceratium malesianum and Proceratium itoi, but Proceratium malesianum is a smaller species (WL 0.71–0.90) with a broadly rounded vertex (weakly convex, almost straight in Proceratium itoi) and a broadly rounded petiolar node in profile (posterior face of petiolar node in profile steeper than anterior face in Proceratium itoi).

Volumetric raw data (in DICOM format), a 3D rotation video (in .mp4 format, see Suppl. material 4: Video 2), still images of surface volume rendering, a 3D surface (in PLY format), and montage photos illustrating the head, profile and dorsal views of the body of a non-type specimen (OKENT0016142) were all generated as part of this study (Staab et al 2018). Data and images are freely available for download from a Dryad repository (there is a download link at the top right of the webpage) and a 3D surface model can be viewed online at Sketchfab.

Keys including this Species


China, Japan and Republic of Korea.

Staab et al. (2018) - This species is widely distributed, occurring from Japan (except Hokkaido) and South Korea to Vietnam. It has been recorded from Taiwan and the Chinese provinces Zhejiang and Hunan. Thus, we expect that it will be collected from the geographically intermediate provinces in the future.

Distribution based on Regional Taxon Lists

Oriental Region: Taiwan.
Palaearctic Region: China, Japan (type locality), Republic of Korea.

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


Staab et al (2018) - No direct biological observations from China are available, but the Japanese populations are comparatively well studied (Onoyama and Yoshimura 2002). Nests are found in the soil or rotting wood of various deciduous or evergreen forest types and workers forage hypogeic or in leaf litter. Mature colonies have 100–200 workers and densities can reach 0.3 colonies per m² (Masuko 2010). Larval hemolymph feeding has been observed (Masuko 1986).

Masuko (2019) describes larval hemolymph feeding (LHF) in Proceratium itoi, where the queen feeds exclusively on the older final instar larvae by breaking open a specialized dorsal area. Proceratium itoi are predatory on spider eggs, and it is intriguing that the queen does not feed directly on this easy prey. It is possible that the larvae function as a filter, affording protection against toxins or parasites. Importantly, trophallaxis is lacking among the adults in almost all poneroid ants, so it is unsurprising that other trophic behaviours exist instead. Intuitively, ant queens are privileged beneficiaries of LHF exchanges given that their higher fecundity benefits colony fitness. The larvae that are subjected to LHF successfully eclose as adults. However, this vampirism unavoidably slows down larval growth, causing a cost to the colony. This seems to be confirmed by the absence of LHF in small incipient colonies. Although wounds quickly close by coagulation of hemolymph and cuticular melanization, LHF may be favoured by the high degree of hygiene inside ant nests. (Vampirism in the ant Proceratium itoi)


Economo-header (  X-ray micro-CT scan 3D model of Proceratium itoi (worker) prepared by the Economo lab at OIST.

See on Sketchfab. See list of 3D images.


The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • itoi. Sysphincta itoi Forel, 1918a: 717 (w.) JAPAN. Ogata, 1987: 107 (m.); Onoyama & Yoshimura, 2002: 35 (q.). Combination in Proceratium: Brown, 1958g: 247. See also: Baroni Urbani & De Andrade, 2003b: 267.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.



Baroni Urbani and de Andrade (2003) - Head longer than broad, its sides weakly convex. Vertex in full face view almost straight. Clypeus medially reduced, triangular, between and slightly longer than the antennal socket. Clypeal dorsum with a longitudinal carina. Antenna1 socket with broad torulus. Frontal carinae far (sic) each other, partially covering the antennal insertions. Frontal area behind the frontal carinae convex. Lateral expansions of the frontal carinae relatively narrow, raised, diverging. Genal carinae prominent. Eyes small, represented by a dark dot below the integument. Eyes on the midline of the head. First funicular joint subequal in length and width. Funicular joints 2-10 much broader than long. Last funicular joint about as long as the sum of joints 7- 10. Scapes clearly not reaching the vertexal margin and gently thickening apically. Masticatory margin of the mandibles with 3-4 denticles before the pointed apical tooth. Palp formula 4,3.

Mesosoma slightly longer than the maximum head length (mandibles included). Promesopleural and meso-melapleural sutures impressed ventrally only. Basal face of the propodeurn weakly declivous. Declivous face of the propodeum gently concave. Basal and declivous faces of the propodeum separate laterally by a weakly carinate angle. Sides of the declivous face of the propodeum carinate. Propodeal lobes surrounded by a narrow lamella. Propodeal spiracle round and above mid height in lateral view.

Petiole in profile with declivous anterior face and convex posteriorly. Petiole in dorsal view with diverging sides and convex posteriorly. Anterior border of the petiole variably concave and carinate, the carina dcnticulate on each side. Ventral process of the petiole small and triangular. Postpetiole anteriorly broader than the petiole; its sides diverging or gently convex. Postpetiolar sternite anteromedially with a weakly marked subtriangular projection. Postpetiolar sternite straight in side view. Constriction between postpetiole and first gastral segment impressed. Gastral tergite I strongly convex on the curvature. Remaining gastral tergites and sternites curved ventrally.

Legs slender but not very elongate. All tibiae with a pectinate spur. Spurs of fore legs without a basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/4 shorter than hind tibiae. Second tarsomere of hind legs shorter than pretarsus. Pretarsal claws simple. Arolia present.

Sculpture. Head, mesosoma, petiole and postpetiole granulate. First gastral tergite smooth and covered by piligerous punctures; its sides and the posterior border with additional granulation. Legs granulate, the granulation less marked than in the other body parts.

Pilosity. Body covered by hairs of three main types: (1) short, dense, subdecumbent on the whole body, sparse and suberect on the funicular joints; (2) longer than type (I), sparse, erect or suberect on the whole body, slightly shorter on the scapes, absent on the funiculi; (3) shorter than hair type (I), dense and decumbent on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, sparse hairs.

Colour brown.

Measurements in mm and Indices: TL 3.65-3.82; HL 0.81-0.83; HW 0.71-0.74; EL 0.03; SL 0.49-0.50; WL 1.00-1.04; PeL 0.32-0.35; Pew 0.31-0.32; HFeL 0.64; HTiL 0.53-0.56; MBaL 0.38-0.41; LS4 0.25-0.30; LT4 0.86-0.92; CI 87.6-89. I; SI 60.2-60.5; IGR 0.34-0.35.


Baroni Urbani and de Andrade (2003) - Differing from the worker in the following details: eyes about 1/5 of the head length and with well defined ommatidia. Ocular pilosity present. Ocelli present.

Mesosoma robust. Scutellum large; its sides converging into a convex posterior border. Basal face of the propodeum gently declivous posteriorly; dorsally medially incised and as flat as the declivous face; its sides subangulate and carinate. Metanotum without denticle. Propodeal lamellae narrower.

Measurements in mm and Indices: TL 4.46-4.62; HL 0.86-0.88; HW 0.78-0.8 1 ; EL 0.17; SL 0.5 1; WL 1.28- 1.32; ; PeL 0.38-0.40; Pew 0.37; HFeL 0.75; HTiL 0.61 -0.62; HBaL 0.46; LS4 0.36-0.38; LT4 1.10- 1.12; CI 90.7-92.0; SZ 57.9-59.3; ICR 0.33-0.34.


Head subequal in size or slightly broader than long. Vertex in full face view convex. Vertexal margin carinate. Clypeus dorsomedially convex. Frontal carinae thin, low, diverging posteriorly. Frontal area with a sulcus. Ocelli large. Compound eyes large and placed mostly on the anterior part of the head sides. Scapes reaching the anterior ocellus. First funicular joint about 1/4 shorter than second joint. Joints 2-12 longer than broad. Last funicular joint slightly longer than the sum of joints 10-11. Mandibles edentate and only with a pointed apical tooth. Palp formula 4,3.

Mesosoma robust. Pronotum and anterior third of rnesonotum almost perpendicular to the posterior two thirds of the mesonotum. Posterior two thirds of mesonotum almost flat. Parapsidal furrows marked. Scutellum slightly higher than the mesonotum; its posterior border round. Basal and declivous faces of the propodeum convex in side and dorsal view. Sides of the propodeum gently converging. Declivous face of propodeum laterally superficially carinate. Metanotum with a median tooth. Propodeal lobes round and partially lamellaceous. Propodeal spiracles small.

Petiole in profile declivous in the anterior third and convex in the two posterior thirds. Sides of the petiole convex in dorsal view. Anterior border of the petiole concave and laterally carinate. Subpetiolar process absent; petiolar sternite gently convex. Postpetiole anteriorly broader than the petiole; postpetiolar sides diverging posteriorly. Anterior border of the postpetiolar sternite with a superficial triangular "lip". Gastral tergite I large and convex in side view. Remaining gastral tergites and sternites slightly curved ventrally.

Legs as in the worker but more elongate. Hind basitarsi slightly shorter than hind tibiae.

Fore wings of our type 2, hind wings of our type 3 as defined in the description of the genus.

Genitalia as in Fig. 114.

Sculpture. Head irregularly reticulorugose. Mesosoma minutely granulopunctate, the granulation more superficial on the mesonoturn. Scutellum, propodeum and pleurae with additional, thin, irregular rugosities. Postpetiole and gaster smooth and with minute piligerous punctures. Legs minutely granulopunctate.

Pilosity as in the worker but with hairs of type (2) sparser on the petiole, postpetiole and gaster.

Colour. Back with lighter antennae and legs.

Measurements in mm and Indices: TL 3.63-3.74; HL 0.59-0.60; HW 0.61-0.64; EL 0.30-0.31; SL 0.33; WL 1.20-1.28; PeL 0.34-0.35; PeW 0.25-0.26; HFeL 0.76-0.79; HTiL 0.65; HBaL 0.58-0.60; LS4 0.48; LT4 0.84; CI 103.4-106.7; SI 55.0-55.9; IGR 0.57.

Type Material

Worker. Type locality. Tokyo, Japan Type materlal 3 syntype workers labelled "Sysphincta itoi" For, worker type, Tokio, Japan (Ito)" in Musee d'Histoire Naturelle Genève, examined.