Short Communication |
Corresponding author: Rainer Neumeyer ( rainer.neumeyer@terra-typica.ch ) Academic editor: Stefan Schmidt
© 2021 Rainer Neumeyer, Jürg Sommerhalder, Stefan Ungricht.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Neumeyer R, Sommerhalder J, Ungricht S (2021) First observation of an ant colony of Formica fuscocinerea Forel, 1874 invaded by the social parasite F. truncorum Fabricius, 1804 (Hymenoptera, Formicidae). Alpine Entomology 5: 23-26. https://doi.org/10.3897/alpento.5.67037
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In the northern Alps of Switzerland we observed a mixed ant colony of Formica truncorum Fabricius, 1804 and F. fuscocinerea Forel, 1874 at the foot of a schoolhouse wall in the built-up centre of the small town of Näfels (canton of Glarus). Based on the fact that the habitat is favorable only for F. fuscocinerea and that F. truncorum is a notorious temporary social parasite, we conclude that in this case a colony of F. fuscocinerea must have been usurped by F. truncorum. This is remarkable, as it is the first reported case where a colony of F. fuscocinerea has been taken over by a social parasite. We consider the observed unusually small workers of F. truncorum to be a starvation form. This is probably due to the suboptimal urban nest site, as this species typically occurs along the edge of forests or in clearings.
Central Europe, northern Alps, social insects, temporary social parasitism, urban ecology
Parasitism is an extremely common life history strategy. Adopting a broad definition – obligate feeding on a living organism without (at least immediately) causing the death of the host – about half of all animal species can be considered parasites (
There are 24 ant species of the genus Formica Linnaeus, 1758 recorded from Switzerland (
Most species of the subgenus Serviformica are predominantly monodomous, that is the population of the whole colony is united in a single nest. These species are generally prone to social parasites (
In the course of inventorying the ants of selected reserves in the canton of Glarus located in the northern Alps of Switzerland, we also tried to locate some of the hitherto missing species from the Formica cinerea group in built-up areas not existing in the reserves. We collected the ants by hand or using a small insect aspirator (pooter). The ants were killed and preserved in ethanol (80%). They were examined with the help of a stereo microscope (Olympus SZH10) with ring illumination using magnifications between 10× and 70×. The specimens were identified by Rainer Neumeyer following the key in
Searching our study area for colonies of Formica fuscocinerea we discovered one small colony in sandy soil between cobble stones along the building wall. At the nest entrance we not only found workers of Formica fuscocinerea (Fig.
The workers of Formica truncorum were all below average in size – hardly larger than the workers of the host species F. fuscocinerea – and at first sight they resembled small workers of Formica rufa Linnaeus, 1761 in terms of their dark pigmentation, especially on the head (Fig.
We observed the nest entrance for 15 minutes in sunny and windless conditions at 21 °C, counting a total of five workers (one Formica fuscocinerea and four F. truncorum) returning to the colony and eleven (four Formica fuscocinerea and seven F. truncorum) emerging from the colony. Along the south- and west-facing wall of the school building we found three additional ant species, namely Lasius emarginatus Olivier, 1792, Myrmica sabuleti Meinert, 1861 and Tetramorium impurum (Förster, 1850). When we returned to the site on 17th September 2020, the nest entrance had apparently shifted almost a meter to the west in the meantime. However, this does not necessarily mean that the colony had also moved its underground nest chambers.
All species of Formica subgenus Formica occurring in Switzerland – including Formica truncorum – can establish their colonies as interspecific temporary social parasites of colonies of certain species of Formica subgenus Serviformica (
As we have seen, common nests of F. truncorum and F. fuscocinerea are likely to remain the exception, if only because the two species generally colonize different habitats and accordingly encounter each other at most in transitional areas. In addition, Formica fuscocinerea is known to form vigorous supercolonies (
Nanitic workers are somewhat smaller than usual ones. They are rather characteristic of the initial phase of a colony founded claustrally, i.e. by independent colony foundation in a closed cavity (founding chamber) by a single, recently mated female (
Bernhard Seifert (Görlitz) verified the identification of the voucher specimens. Elisabete Nunes Coelho (Dottikon) assisted in the field. Oliver Yves Martin (Zürich) read and improved the manuscript. So did also Georg Fischer (Okinawa) and an anonymous reviewer from Dietikon. Dezian Melissa Lloyd (Männedorf) refined the edited video. We thank them all for their help. Our friend and fellow entomologist Edwin Kamer – a local teacher at the described school in Näfels – provided access to the school yard. The ant inventory of selected reserves in the canton of Glarus was commissioned by the Abteilung Umweltschutz und Energie (Jakob Marti, Peter Zopfi, Anahita Aebli).