SCHIFANI: First Record of the Vulnerable Social Parasite Ant Plagiolepis Grassei in Italy(Hymenoptera: Formicidae)

First Record of the Vulnerable Social Parasite Ant Plagiolepis Grassei in Italy
(Hymenoptera: Formicidae)


The first Italian records of the rare parasitic ant species Plagiolepis grassei Le Masne, 1956 are here reported. This species is considered as “Vulnerable” by the IUCN’s Red List, and was previously recorded from France and Spain only.


Plagiolepis Mayr is a genus of minute formicine ants widespread across temperate and tropical regions of the Old World (Robertson 2000), consisting of 61 valid species and 19 valid subspecies (Bolton 2016). Unfortunately, no modern taxonomic revision of the genus exists. Plagiolepis grassei Le Masne belongs to a group of social parasites permanently living (i.e. “inquiline”, sensu Wilson 1971) in colonies of other Plagiolepis species, and its host is P. pygmaea (Latreille, 1798).

Social parasitism is a widespread biological adaptation among ants, shared by phylogenetically distant and mostly holarctic taxa. At least further eight parasite Plagiolepis species are known so far (Buschinger 2009).

Le Masne (1956) described P. grassei and compared it to the workerless inquiline P. xene Stärcke, 1936, and to their host P. pygmaea. Le Masne (l.c.) considered those species as morphologically closely related, and thought they were clearly distinct from any other Mediterranean Plagiolepis. Moreover, by observing the differences in queens and workers size, and the presence/abundance of workers as well, Le Masne (l.c.) hypothesized each of the three species as a possible evolutionary step. These steps are represented by a free-living species (P. pygmaea), from which the other two originated: an intermediate parasite species (P. grassei), with smaller queen and a limited number of workers, and a highly specialized workerless parasite with tiny queens (P. xene). Contributions to the knowledge of the biology of P. grassei came from Passera (1967, 1969, 1970, 1977), while a genetic investigation by Trontti et al. (2006b) shows P. grassei fits the so-called (although sometimes questionable) “Emery’s rule” (see Emery, 1909), about the origin of parasitic ants from their close relatives serving as host.

P. grassei was firstly collected in France, in the Eastern Pyrenees (Le Masne 1956) (from where it was also reported by Trontti et al. (2006a) near Cerbère), and was later found at Pontevedra, Galicia, Spain (Espadaler 1979). In May 2016, it was also found at two additional French sites, namely La Javie (N44°12'43'', E6°17'1'') and Pompignan (N43°53'6'', E3°50'1'') (R. Blatrix, pers. comm.). In 1996 the species was listed as VU (vulnerable) in the IUCN red list by the Social Insects Specialist Group (together with two other social parasitic European Plagiolepis: P. ampeloni (Faber, 1969) and P. regis Karavaiev, 1931). Considerations about genetic vulnerability and conservation of P. grassei were expressed by Trontti et al. (2006a) in relation to its weak dispersal capabilities and estimated small population.

Materials and methods

Italy: Sicily, Palermo, Gole del Drago, N37°51'56'' E13° 18'2'', 450 m, 1 May 2016, E. Schifani legit, 4 ♀♀ (E. Schifani personal collection); Sicily, Palermo, Monte Pellegrino, N38°10'22'', E13°21'5'', 400 m, 31 May 2016, E. Schifani legit, 2 ♀♀ (E. Schifani personal collection).

All of the specimens are preserved in 95% ethanol. All the queens were collected under stones, from two nests (one at each collecting site) of Plagiolepis pygmaea, in areas where the latter is very abundant. Few queens of P. xene were also found in both nests, but no workers of P. grassei could be detected (even though no careful search was carried out in order to find them). The first site was characterized by an open landscape with low Mediterranean maquis, in some parts degrading towards garrigue, while the second consisted of an artificial Pinus and Eucalyptus reforestation. At both sites carbonatic rocks were very abundant. The specimens were identified by means of a stereomicroscope, according to the diagnostic features pointed out by Le Masne (1956) and Bernard (1967).


The present discovery greatly extends the known distribution range of this rarely collected species. Plagiolepis grassei occurs in low numbers inside nests of P. pygmaea and can be easily overlooked. Consequently, it probably occurs elsewhere, and its “rarity” is partially influenced by the difficulty to detect it in the field (an issue also raised by Espadaler X. & López-Soria 1991, regarding parasite ants in Spain). Even the present day evaluation of its conservation status may be considered as provisional (as well as for P. regis and P. ampeloni). Nonetheless, general caution and concern appear to be justified also for the reasons expressed by Trontti et al. (2006a) regarding genetic vulnerability of the parasitic ants of the genus Plagiolepis.


I am grateful to Maurizio Sarà (University of Palermo) for allowing me to use a powerful stereomicroscope to examine the studied specimens, and to Bruno Massa (University of Palermo) for his corrections and advices. I also wish to thank Fabrizio Rigato (Museo Civico di Storia Naturale, Milan) for his revision of the manuscript together with Paolo Audisio (Sapienza University of Rome) and an anonymus referee. I also thank Rumsaïs Blatrix (Centre d’Écologie Fonctionnelle et Évolutive – CNRS, Montpellier) for sharing with me his recent observations of Plagiolepis grassei from new French sites. I express my gratitude to Marcello Romano for providing quality images of the specimens.



F Bernard. 1967. Faune de l’Europe et du Bassin Méditerranéen. 3. Les fourmis (Hymenoptera Formicidae) d’Europe occidentale et septentrionale. Masson, Paris, 411 pp.


B Bolton. 2016. An online catalog of the ants of the world. Available from (accessed 06/07/2016).


A Buschinger. 2009. Social parasitism among ants: a review. (Hymenoptera: Formicidae). Myrmecological News, 12: 219–235.


C Emery. 1909. Über den Ursprung der dulotischen, parasitischen und myrmekophilen Ameisen. Biologisches Centralblatt, 29: 352–362.


X Espadaler. 1979. Citas nuevas o interesantes de hormigas (Hym. Formicidae) para España. Boletín de la Asociación española de Entomología, 3: 95–101.


X. Espadaler, L. López-Soria 1991. Rareness of certain Mediterranean ant species, fact or artifact? Insectes Sociaux, 38: 365–377.


W Faber. 1969. Beiträge zur Kenntnis sozialparasitischer Ameisen. 2. Aporomyrmex ampeloni nov. gen., nov. spec. (Hym. Formicidae), ein neuer permanenter Sozialparasit bei Plagiolepis vindobonensis Lomnicki aus Österreich. - Pflanzenschutz Berichte, 39: 39–100.


G. Le Masne 1956. Recherches sur les fourmis parasites. Plagiolepis grassei et l’évolution des Plagiolepis parasites. - Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, 243: 673–675.


L Passera. 1967. Inhibitions interspécifiques déclenchées par les femelles fécondes des fourmis parasites Plagiolepis xene St. et Plagiolepis grassei Le Mas. Pas. Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, 265: 1721–1724.


L Passera. 1969. Observations biologiques sur la fourmi Plagiolepis grassei Le Masne Passera, parasite social de Plagiolepis pygmaea Latr. (Hym. Formicidae). Insectes Sociaux, 15: 327–336.


L Passera. 1970. Biologie de la reproduction chez Plagiolepis pygmaea Latreille et ses deux parasites sociaux Plagiolepis grassei Le Masne et Passera et Plagiolepis xene Stärcke (Hymenoptera Formicidae). Annales des sciences naturelles. Zoologie et biologie animale, (12)11: 327–481.


L Passera. 1977. L’absence d’effet royal chez les ouvrières gynécoïdes de la fourmi parasite social Plagiolepis grassei (Hym. Formicidae). Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, 285: 1447–1449.


H.G. Robertson 2000. Afrotropical ants (Hymenoptera: Formicidae): Taxonomic progress and estimation of species richness. Journal of Hymenoptera Research, 9: 71–84.


Social Insects Specialist Group 1996. Plagiolepis grassei. The IUCN Red List of Threatened Species 1996: e.T17464A 7087398. Downloaded on 11 July 2016.


K. Trontti, S. Aron, L. Sundström 2006a. The genetic population structure of the ant Plagiolepis xene – implications for genetic vulnerability of obligate social parasites. Conservation Genetics, 7: 241–250.


K. Trontti, R. Savolainen, L. Passera 2006b. Phylogenetic origins of the inquiline ants Plagiolepis grassei and Plagiolepis xene. Manuscript in: “Trontti K.: Population structure and evolution in the ant Plagiolepis pygmaea and its two social parasites Plagiolepis xene and Plagiolepis grassei. PhD thesis. Yliopistopaino 2006. ISBN 952-92-0383-7 (printed) / ISBN 952-10-3170-0 (pdf)”


E.O. Wilson 1971. The insect societies. Belknap Press of Harvard University Press, Cambridge, Mass., x + 548 pp.

Fig. 1

Two Plagiolepis grassei queens (1) and two P. xene queens (2) among workers of P. pygmaea (3) photographed under a stone. Gole del Drago, Palermo, Italy. Photo by Enrico Schifani.

Fig. 2

Plagiolepis grassei queen in full-face view. Specimen collected in Monte Pellegrino, Palermo, Italy. Photo by Marcello Romano.

Fig. 3-4

Plagiolepis grassei queen in dorsal and body profile view. Specimen collected in Gole del Drago, Palermo, Italy. Photo by Marcello Romano.

Abstract views:


Article Metrics

Metrics Loading ...

Metrics powered by PLOS ALM

Copyright (c) 2017 Enrico Schifani

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
© PAGEPress 2008-2018     -     PAGEPress is a registered trademark property of PAGEPress srl, Italy.     -     VAT: IT02125780185     •     Privacy