Introduction to Beetle Inquilinism and Systematics of the Histerid Subfamily Hetaeriinae
A. K. Tishechkin and C. E. Carlton
Click on links to see pages illustrating various taxa that are discussed.
Representatives of numerous insect taxa, most notably within the orders Coleoptera and Diptera, successfully exploit social insects by living in their nests and relying on them for food and protection. This type of symbiosis is known as inquilinism. More specifically, widespread forms of inquilinism are named in relation to social insect hosts, myrmecophily and termitophily (ant- and termite-associated, respectively). In common terminology in reference to these systems, the host is always the social insect that the inquiline occurs with, and the guest is the inquiline itself.
This page and those linked to it reflect a systematic specialization of some LSAM staff members on beetle families richly represented by myrmecophilous and termitophilous taxa with emphasis inquilinous members of the Histeridae, the subject of a current systematic research initiative.
From the guests' points of views, social insect colonies represent sources of abundant food resources that are well protected and sheltered by aggressive and behaviorally sophisticated hosts. Naturally, the adaptations that allow guests to exploit host colonies and overcome their defenses vary among different species. They often involve some of the most bizarre morphologies and behaviors in the animal kingdom. The first classification of social insect inquiline types (Wasmann 1903) reflected host attitudes towards guests, which were subdivided into:
synechtrans (persecuted guests)
synoeketes (indifferently tolerated guests) and
symphiles (welcome guests).
David Kistner (1979) discussed this classification in length and came up with a modified classification. He stressed the importance of guest integration into host societies and subdivided the variety of host-guest associations into two major types:
poorly specialized, non-integrated species and
completely integrated species.
Levels of guest integration into the colony fabric of daily life defines their position in a gradient of degrees of colony resource use, ranging from occasional foraging on the periphery of the colony or in refuse deposits to whole life cycles spent inside colonies being treated as host nestmates. We like to use the anthropomorphic analogy to humans keeping pets as part of the household, though of course the comparison is not valid in any intellectual sense to the hosts. Morphological and behavioral mechanisms allowing such integration are variable and often extremely sophisticated in guests. Myrmecophiles and termitophiles are often very different from their non-inquline relatives and possess a vast variety in strange adaptive morphologies (exemplified in images below). Kistner's (1979) excellent review contains major conceptual issues and discussions of numerous issues of social insect inqulinism.
Beetles maintain their reputation as the most diverse terrestrial arthropods in inquilinous insect systems as well. Only Diptera comes close to Coleoptera in terms of inquiline diversity, but most of it is associated with an enormous radiation within fly family Phoridae. Distribution of mymecophyly and termitophily, as well as melittophyly (bee-associated) and sphecophyly (wasp-associated), in beetles is much more widespread and evenly distributed across the order. Major inquiline lineages occur in Carabidae (e.g. Paussinae), Ptiliidae (e.g. Cephaloplectinae, considered earlier as family Limulodidae), Staphylinidae (numerous taxa in Aleocharinae, Pselaphinae, Staphylininae and Tachyporinae), Histeridae (see below), several groups of Scarabaeoidea (e.g., within Aphodiinae, Ceratocanthinae, Cetoniinae and Scarabaeinae) and Tenebrionidae (numerous genera from different lineages). In addition, more than 20 families contains less numerous inquiline representatives (see review in Kistner 1982), including specialized odd genera in Anobiidae, Chrysomelidae, Salpingidae.
Here we present more detailed information on a family, Histeridae, that includes many inquilinous species, including two exclusively inquilinous subfamilies. The Histeridae includes about 4,000 described species distributed worldwide (Mazur 1997). Histerids are small to medium-sized beetles (0.7-25 mm) that occur in many habitats, from dense forests to deserts and dunes, where most are predators of beetle, fly and flea larvae. They live in a variety of decomposing organic materials (dung, carrion, rotten wood, seaweed, and forest litter), under loose bark of woody plants, in galleries of wood-boring insects, vertebrate nests, and rhizospheres of desert plants. Specialized soil and cave-dwelling species are also included.
Myrmeco- and termitophily have evolved several times in Histeridae (Caterino & Vogler 2002). These associations occur among the representatives of eight out of 11 traditionally recognized subfamilies. Two of them, Chlamydopsinae and Hetaeriinae, consist exclusively of inquilinous species. Other subfamilies contain few specialized genera, though several ant-associated species occur in many otherwise non-inquilinous genera.
The Chlamydopsinae is an Australasian group distributed from India and Japan to Australia and New Guinea reaching Oceania as far East as Fiji. Currently, 12 genera with 176 species are known and many more remain to be discovered and described. The recent surge in taxonomic activities on chlamydopsines has resulted in 3.5 fold increase in species numbers just in the last decade. Chlamydopsine host records list 10 ant genera in Dolichoderinae, Formicinae, Myrmicinae and Ponerinae, and one termite genus. Systematics and life history information for the subfamily was recently reviewed by Caterino & Degallier (2007). Many more images of these remarkable beetles are available at http://www.sbnature.org/collections/invert/entom/histeridae.htm#chlams
The Hetaeriinae is a diverse, almost exclusively neotropical subfamily containing about one-third of the World and two-thirds of neotropical histerid genera and about 20% of all described neotropical species. Approximately 100 genera with 240 described species occur in the neotropics. In addition, the subfamily contains one Holarctic genus with 26 species in North America and six in the Palearctic region, a monotypic Nearctic genus, and three nearly exclusively Mediterranean genera containing 50 species. Four genera are shared between neotropical and nearctic regions. And as with chlamydopsines, many more genera and species await discovery and description. For example, as of December 2007 the LSAM database of Hetaeriinae in World collections contained records for 5,123 specimens belonging to 745 species. On fact, Hetaeriinae may be the most diverse obligately inquilinous lineage of insects, with rivals potentially found only among some Staphylinidae and Phoridae (Seevers 1965; Kistner 1982).
Published data on host-guest associations of Hetaeriinae are abundant but fragmentary. Most data were gathered by early 20th century naturalists, such as C. Bruch, F. Nevermann, F. Plaumann, H. Schmidt, P. Schwarmaier and F. Zikan. More recent data were gathered by R. Akre, N. Degallier, P. Kovarik, C. Rettenmeyer and A. Tishechkin during the 1950-2000s through direct collecting from host nests.
Left to right: Early-mid 20th century collectors and describers of inquilinous beetles, Argentinean collector Carlos Bruch (1869-1943). A. Reichensperger (1878-1962), who described many taxa but almost never went collecting outside central Europe, and a scene at a leafcutter ant excavation in Kisatchie National Forest, Louisiana, C. Carlton, background, A. Cline, R. Leschen and Fosterdog (1993-2006), foreground.
At present, hosts are known for 77 genera (ca. 70% of described genera) of Hetaeriinae, including three or more independent host records available for 57 genera. Diverse host taxa are represented among hetaeriines. Host termite genera in the Neotropics include Cornitermes, Nasutitermes, Syntermes, and Termes (Nasutitermitinae and Termitinae in Termitidae). Ant genera are more numerous as hosts of hetaeriines, including Eciton, Labidus, Neivamyrmex, and Nomamyrmex within the Ecitoninae (army ants); Acromyrmex, Atta, Pheidole, and Solenopsis within the Myrmicinae; Ectatomma, Holcoponera, and Pachycondyla within the Ponerinae Army ants harbor the most diverse hetaeriine assemblages. Ant genera that serve as hosts of hetaeriines outside the Neotropics include Tapinoma within the Dolichoderinae, Acantholepis, Formica and Lasius within the Formicinae, and Aphaenogaster and Tetramorium within the Myrmicinae.
In 1985, a review of the Neotropical genera of Hetaeriinae was published (Helava et al. 1985). Although not completely comprehensive, it boosted systematic research on the group. Two tribes and 26 genera have been described or redescribed since its publication, and two phylogenetic studies provided an evolutionary hypothesis for one tribe (Tishechkin 2007) and presented the first molecular phylogeny for the subfamily (Caterino & Tishechkin 2006). We plan to continue and expand research on systematics and natural history of the Hetaeriinae with an eventual target of revising the taxonomy and evolutionary relationships of the group. The following linked pages are examples of our future approach to internet presentation of some results of our work
Caterino, M. S. and N. Degallier. 2007. A review of the biology and systematics of Chlamydopsinae (Coleoptera: Histeridae). Invertebrate Systematics 21: 1-28.
Caterino, M. S., and A. K. Tishechkin. 2006. DNA identification and morphological description of the first confirmed larvae of Hetaeriinae (Coleoptera: Histeridae). Systematic Entomology 31: 405-418.
Helava, J. V. T., H. F. Howden, and A. J. Ritchie. 1985. A review of New World genera of myrmecophilous and termitophilous subfamily Hetaeriinae (Coleoptera: Histeridae). Sociobiology 10: 127-386.
Kistner, D. H. 1979. Social and evolutionary significance of social insect symbionts. Pp. 339-413 in: H.R. Hermann (ed.) Social Insects. Vol. I. Academic Press, New York.
Kistner, D. H. 1982. The socials insects' bestiary. Pp. 1-244 in: H.R. Hermann (ed.) Social Insects. Vol. III. Academic Press, New York.
Seveers, C.H. 1965. The systematics, evolution and zoogeography of staphylinid beetles associated with army ants (Coleoptera, Staphylinidae). Fieldiana. Zoology 47: 139-351.
Tishechkin, A. K. 2007. Phylogenetic revision of the genus Mesynodites Reichardt, 1924 (Coleoptera: Histeridae: Hetaeriinae) with description of new tribes, genera and species. Sociobiology 47: 1-167.