Thomas Parmentier, Jean-Yves Baugnée, Simon Braem, Roger Cammaerts, David Ignace & Wouter Dekoninck

Recent and old records of the rare myrmecophilous beetle Haeterius ferrugineus (Olivier 1789) in Belgium, Luxembourg and North-East of France

Résumé

Haeterius ferrugineus (Olivier 1789) est un coléoptère histéride rarement observé qui réside dans des fourmilières. Nous fournissons les premières observations de cette espèce en Flandre, et présentons un aperçu de toutes les observations de cette espèce en Belgique, dans le Grand-Duché de Luxembourg et dans la région frontalière du Nord de la France, au cours des 150 dernières années.

Abstract

Haeterius ferrugineus (Olivier 1789) is a rarely observed histerid beetle which lives permanently in ant nests. We provide the first records of this species in Flanders, the northern part of Belgium, and give an overview of the scattered records for this species in Belgium, Grand-Duché of Luxembourg and the border region in the North of France gathered over the past 150 years.

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Reçu le 12 septembre 2023, accepté le 20 novembre 2023

Cet article est distribué suivant les termes et les conditions de la licence CC-BY (http://creativecommons.org/licenses/by/4.0/deed.fr)

INTRODUCTION

1A remarkably number of beetle species strictly lives inside ant nests (Parker, 2016; Parmentier et al., 2020; Hölldobler & Kwapich, 2022). Most of these myrmecophilous species are only occasionally recorded and the distribution and biology of many of them remains obscure. The Histeridae (clown or hister beetles) is a large family of beetles living in a wide variety of habitats encompassing dead wood, dung, nests of vertebrates and nests of social insects (Helava et al., 1985). The latter strategy is especially well developed in the Haeteriinae subfamily, where all members are associated with ants or termites. Like other histerids they are characterized by a convex and robust body with short retractable appendages (Parker, 2016). The heavily sclerotorized, protective morphology helps to survive in ant nests. In addition, some of these Haeteriines resort to specialized strategies, such as chemical deception and appeasement of the host (Lenoir et al., 2012; Parmentier et al., 2017). The Haeteriinae subfamily has its biggest radiation of myrmecophiles in the neotropics. This is especially the case for species associated with army ants (Helava et al., 1985) where some spectacular representatives evolved (von Beeren & Tishechkin, 2017). In Europe, four genera of Haeteriine beetles can be found: Satrapes, Sternocoelis, Eretmotus, and Haeterius. Among these, Haeterius ferrugineus is the sole species belonging to the Haeterius genus. It has the broadest distribution of all European Haeteriines, but records are sparse and scattered (Wasmann, 1894; Donisthorpe, 1927; Vallenduuk, 1987; Secq & Secq, 1996; Hlaváč & Lackner, 1998; Lapeva-Gjonova, 2013; Cuesta Segura & García García, 2014; Benisch, 2023; GBIF Secretariat, 2023).

2Haeterius ferrugineus is a small (1.3-2.0 mm) reddish brown histerid with relatively long and flattened legs. It has sparse erect pale setae on the pronotum and elytra (Figure 1). This beetle has been the centre of fascination for entomologists for a long time. Pioneering entomologists Charles Janet and Erich Wasmann were the first to make detailed observations on its biology and were able to keep individuals for four years in laboratory nests (Janet, 1897; Wasmann, 1905). They observed that this beetle reaches a high level of integration into the colony. They rarely incite aggression, but if they do so, they resort to feigning dead. They are frequently licked by the ants which suggests that they have exocrine glands that appease the ants. They climb on the pupae and larvae and they are carried around by the ants (Wasmann, 1905) (Figure 1).

Figure 1 : Photos of Haeterius ferrugineus (Olivier 1789) and its interaction with the ant brood and host. a) Detail photo of a prepared specimen (© David Ignace). b) Individual crawling on the F. fusca host brood, note the rove mite on the ant pupa. c) Two individuals on a F. fusca larva. The erect setae on the beetle elytra are visible. d) Two individuals among ant brood and the F. fusca host: three workers and a queen (© Thomas Parmentier).

3Another peculiar behavior is the waving with the forelegs. It is assumed that this behavior draws the ant’s attraction and may even lead to mouth-to-mouth food exchange. But probably they mainly scavenge on dead ants and prey and occasionally feed on ant brood (Hölldobler & Kwapich, 2022). They have been reported in nests of a large number of ant species (Wheeler, 1908; Parmentier et al., 2020), but their preferred hosts appear to be Formica ants (Wasmann, 1894; Wheeler, 1908).

MATERIAL & METHODS

4We compiled different unpublished records of this beetle in Belgium, Grand-Duché of Luxembourg and the North-East of France. Historical records were retrieved from RBINS collection voucher specimens and specimens from private collections (Jean-Yves Baugnée, Roger Cammaerts and David Ignace). The most recent records of H. ferrugineus were made during a detailed field study on the distribution and host preference of myrmecophiles in heathland patches south-west of Bruges, Belgium. In this study we collected myrmecophiles in a standardized way by sieving one liter of nest material from 193 ant nests, belonging to 16 ant species.

Table 1 : Overview of the records of Haeterius ferrugineus (Olivier 1789) in Belgium, Luxembourg and North-East of France. Every row represents a record made in a distinct host nest. Every record is mapped in Figure 2 with the number code (NR) of the first column. Records 5, 12 and 15 were previously published.

RESULTS

5We compiled 23 records for H. ferrugineus in Belgium, Luxembourg and North-East of France of which three were previously published. An overview of the records and the number of individuals per nest are given in Table 1. Most records were concentrated in the south of Belgium and the border region of Grand-Duché of Luxembourg and France (Figure 2). Beetles were typically found with F. fusca or the related F. cunicularia (subgenus Serviformica). Our most recent records were found in four F. fusca nests and one F. sanguinea nest in heathland patches around Bruges in the north of Belgium. Interestingly, the beetle here was found in 4 of 36 sampled F. fusca nests and 1 of the 25 sampled F. sanguinea nests but was not recorded in the one liter samples of the nests of co-occurring ant species, such as F. polyctena (N = 21), F. rufa (N = 2), Lasius fuliginosus (N = 8), L. niger (N = 28), L. platythorax (N = 11), L. flavus (N = 26), Myrmica species (N = 31) and Tetramorium (N = 4) species.

Figure 2 : Map with records of Haeterius ferrugineus (Olivier 1789) in Belgium and nearby countries near the Belgian border. Numbers refer to localities mentioned in Table 1.

DISCUSSION

6The beetle Haeterius is a small myrmecophilous beetle that is hard to find in North-West Europe. Our records show that it was typically found in Formica fusca or related Serviformica nests (Wasmann, 1894, 1905; Wheeler, 1908). The association of Haeterius beetles with other ant species may be either accidental or a consequence of social parasitism occurring within Serviformica nests. In particular, colonies of F. fusca and F. cunicularia are often targeted and taken over by red wood ants (Formica rufa group). This makes it easy for Haeterius beetles to associate with the new nest residents. Additionally, the brood of Serviformica nests is frequently raided by slave-making ants like F. sanguinea and Polyergus. It has been observed that the beetles exhibit a fascinating hitchhiking behavior, where they cling onto the raided pupae and are carried and transferred into the slavemaker ant nests (Hönle, 2022).

7Most records in Belgium, but also in other European countries, typically mention one or two beetle specimen per nest (Donisthorpe, 1927; Vallenduuk, 1987; Lapeva-Gjonova, 2013). These records are mainly conducted by lifting stones and observing some specimen at the surface of the nest residing under the stone. During our last survey, we collected an exceptional number of 12 specimen in a single F. fusca nest. For this nest, we excavated a significant portion (approximately 5 liters) and spread the material onto large trays. We added a moist plate made of plaster in the middle of the trays. The ants instinctively collected their brood and sought refuge beneath the moist plaster. Interestingly, beetles were consistently attracted to these brood piles and were readily observed amidst the ant offspring under the plaster. Whenever we lifted the plaster, the ants carried their brood to safety, with the beetles frequently hitching rides on the transported brood (Wasmann, 1905).

8We believe that this beetle is much more abundant than currently recorded. However, its cryptic biology deep inside the brood chambers of ant nests coupled with its small size result in it being overlooked. A more thorough investigation of its distribution, behavior, and host associations would undoubtedly provide valuable insights into the ecology of this fascinating beetle.

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