Formicidae

Workers of Leptanilla, photographed by Alex Wild.

Belongs within: Euaculeata.
Contains: Amblyoponinae, Proceratiinae, Ponerinae, Dorylinae, Cerapachys, Ectatommini, Myrmicinae, Formicinae, Myrmeciinae, Pseudomyrmecinae, Dolichoderinae.

The Formicidae are the ants, a diverse and familiar clade of social wasps with a caste division between wingless workers and winged reproductives, with the female reproductives (the ‘queens’) shedding their wings after mating. An elongate scape (first antennal segment) is present in living ants, but was absent in the Cretaceous Sphecomyrminae (Grimaldi & Engel 2005). The morphology of Sphecomyrma indicates that it was an epigean (above-ground) forager, but two of the most basally diverging living ant lineages, the Leptanillinae and Martialis heureka, are hypogean (below-ground) foragers with reduced pigmentation and eyes. Leptanillinae are found in the tropics of the Old World and are characterised by a two-segmented petiole and twelve-segmented antennae without frontal lobes concealing the base.

Other small subfamilies of ants include the Agroecomyrmecinae, little-known ants from Africa and South America with eyes placed far back on the head and antennae spaced widely apart. The shape of the gaster in Agroecomyrmecinae is also distinctive, with abdominal sternite 4 reduced while the corresponding tergite is much larger and vaulted.

Eureka! It’s an ant!
Published 16 September 2008

But not as we know it.

Martialis heureka Rabeling & Verhaagh in Rabeling et al. 2008 as reconstructed in the original description by Barrett Klein. Scale bar on this and the following image represents 1 mm.

I have learnt through Alex Wild of a paper currently in press for PNAS (Rabeling et al. 2008) describing a new species of ant. With more than 12,000 ant species already on the books, this may sound like something of a non-event, but trust me, it’s not. This new ant, Martialis heureka, has been placed not only in a new genus, but in a whole new subfamily. In fact, Martialis appears to be the sister group to all other living ants. A quick request later, and the lead author, Christian Rabeling, was kind enough to send me a copy of the paper*.

*For those without ready journal access, don’t be afraid to contact authors of articles you might be interested in and ask if they have spare copies. Most researchers will be all too happy to help you.

As yet, Martialis is known only from a single worker specimen collected in 2003 in leaf litter from the Brazilian Amazon. One of the authors had found two workers in a soil sample five years previously, but these specimens were subsequently lost. The species name heureka (Greek for “Give me a towel!”) reflects this history of disappointment and elation. The genus name Martialis refers to the unusual appearance of the specimen which looked like it may as well have come from Mars. Martialis is a pale-coloured, eyeless ant with long, thin, pincer-like mandibles. Because of the absence of eyes and its being found in litter and soil samples, the authors infer that Martialis lives hypogaeically (under the ground) or in some other low-light habitat such as within logs. However, the new species lacks any noticeable adaptations for digging, so it may inhabit pre-existing cavities such as rotting roots or burrows made by other animals. The fine mandibles, unlike those of any other ant, may be used for drawing out soft-bodied burrowing prey such as insect larvae. Features such as the presence of a sting indicate that Martialis belongs to the basal grade of ants, and molecular analysis of the specimen indicated Martialis to be sister to all other ants.

Type specimen of Martialis heureka in side view. From the original description.

Interestingly, Rabeling et al.‘s analysis also corroborates an earlier analysis by Brady et al. (2006) in finding the basalmost clade in the ants other than Martialis to be the Leptanillinae, another small hypogaeic subfamily. If this topology is correct, it is possible that the ancestor of all ants was hypogaeic. However, the current analysis was unable to statistically reject a number of alternative rootings.

The earliest fossil record of ants from the Cretaceous consists of the extinct subfamily Sphecomyrminae and a single species of the basal subfamily “Ponerinae” (Dlussky 1999—recent analyses indicate that the Ponerinae as previously recognised should be divided between a number of subfamilies and I don’t know whether the Cretaceous species would belong to the Ponerinae in the stricter sense). Dlussky (1999) recognises a separate family Armaniidae from the Cretaceous closely related to Formicidae but Wilson (1987) argued that the “armaniids” are most likely winged castes of Sphecomyrminae. While the basal lineages of living ants might be hypogaeic, cryptic forms, the Sphecomyrminae, previously identified by its morphology as sister group to living ants, were wasp-like, probably epigaeic forms. Alternative positions for Sphecomyrminae within the crown clade seem unlikely in light of the absence of other ant fossils from the Cretaceous. I personally suspect that despite their basal position, there is a strong possibility that the hypogaeic lifestyle was acquired independently in Leptanillinae and Martialis rather than being ancestral for living ants as a whole.

What to do with a dead hummingbird
Published 11 November 2011

We’ve all been there: that dead hummingbird is just cluttering things up, you don’t really know what to do with it, but you don’t really want to throw it out because, hey, you never know when that sort of thing might come in handy. Well, fear not! A dead hummingbird can be a very practical thing:

You need never be without a scale bar again!

The above figure, from Archibald et al. (2011), shows a rufous hummingbird Selasphorus rufus alongside the newly described early Eocene giant ant Titanomyrma lubei. This fossil comes from the American Green River Formation, in present-day Wyoming. At 51 mm in length, this is one of the largest known ants, rivalled in the modern fauna only by the marginally longer but possibly less robust driver ant Dorylus wilverthi. The title of largest ant ever goes, so far as we know, to Titanomyrma giganteum (or Formicium giganteum*) from the Messel Formation of Germany.

*There’s a bit of skullduggery in Archibald et al.‘s paper viz. the relative status of the pre-existing genus Formicium and their new genus Titanomyrma, whereby Titanomyrma is not diagnostically different from Formicium, but Formicium is relegated to the status of a form taxon for wing fossils only. This is all above board, ICZN-wise, but I’m not sure I’d condone it.

Living giant ants (which, except for Dorylus, are all under 35 mm) are mostly tropical in distribution, but the locality from which Titanomyrma lubei hails would have been within the Arctic Circle when it was alive (Update: Neil has corrected me: the Green River Formation was not Arctic, but northern temperate). The Eocene was a much seamier time than today and, though not tropical, the Arctic would have been far from a frozen wasteland.

Systematics of Formicidae

Synapomorphies (from Grimaldi & Engel 2005): Eusocial habits, with wingless female caste(s) present; metapleural gland opening on propodeum; petiole present.

<==Formicidae [Formicariae, Formiciformes, Formicoidea, Paleosminthuridae, Poneridae]
    |--Sphecomyrminae [Sphecomyrmidae]BS06
    |    |--CretomyrmaWB03
    |    |--Baikuris mandibularis Dlussky 1987RJ93
    |    |--Dlusskyidris zherichiniWB03, GE05
    |    |--Paleomyrmex Dlussky 1975H02
    |    |    `--P. zherichiniH02
    |    `--Sphecomyrma Wilson & Brown 1967RBV08, V10
    |         |--S. canadensis Wilson 1985P92
    |         `--S. freyi Wilson et al. 1967P92
    `--+--Martialis Rabeling & Verhaagh in Rabeling, Brown & Verhaagh 2008 [Martialinae]RBV08
       |    `--*M. heureka Rabeling & Verhaagh in Rabeling, Brown & Verhaagh 2008RBV08
       `--+--LeptanillinaeRBV08
          |    |--ProtanillaRBV08
          |    `--Leptanilla Emery 1870FT08
          |         |--*L. revelierii Emery 1870TB85
          |         |--L. japonica Baroni Urbani 1977I92
          |         |--L. kubotai Baroni Urbani 1977I92
          |         |--L. morimotoi Yasumatsu 1960I92
          |         |--L. oceanica Baroni Urbani 1977I92
          |         |--L. swani Wheeler 1932TB85
          |         `--L. tanakai Baroni Urbani 1977I92
          `--+--+--AmblyoponinaeRBV08
             |  `--AgroecomyrmecinaeRBV08
             |       |--TatuidrisRBV08
             |       `--AgroecomyrmexP92
             `--+--+--ProceratiinaeRBV08
                |  `--Paraponera [Paraponerinae, Paraponerini]RBV08
                |       `--P. clavataRBV08
                `--+--PonerinaeRBV08
                   `--+--+--DorylinaeBS06
                      |  `--Cerapachyinae [Cerapachyini, Cerapachysii, Prodorylinae]WW90
                      |       |--CerapachysBS06
                      |       `--+--LeptanilloidesBS06
                      |          |    |--L. mckennaeBS06
                      |          |    `--L. nomadaBS06
                      |          `--+--Cylindromyrmex striatusBS06
                      |             `--AcanthostichusBS06
                      |                  |--A. kirbyiBS06
                      |                  `--A. texanusWW90
                      `--+--Dolichoformica helferiGE05
                         `--+--+--EctatomminiBS06
                            |  `--+--MyrmicinaeBS06
                            |     `--FormicinaeBS06
                            `--+--+--MyrmeciinaeBS06
                               |  `--PseudomyrmecinaeBS06
                               `--+--DolichoderinaeBS06
                                  `--AneuretinaeBS06
                                       |--AneuretellusGE05
                                       `--Aneuretus Emery 1893B03
                                            `--*A. simoni Emery 1893B03
Formicidae incertae sedis:
  Huberia striata (Smith 1876)H82
  Brownimecia clavataGE05
  Haidomyrmex cerberusGE05
  StrongylognathusE89a
    |--S. aferE89a
    |--S. caeciliaeES12
    |--S. christophi Emery 1889E89a
    |--S. huberiE89a
    |--S. koreanus Pisarski 1965I92
    `--S. testaceusA71
  Anergates atratulusA71
  Eoponera berryiGE05
  Gerontoformica cretacicaGE05
  Canapone dentataGE05
  ProtoponeGE05
  OxyopomyrmexE89a
    |--O. oculatusE89a
    `--O. saulcyi Emery 1889E89a
  Trapeziopelta malignaE89b
  Lordomyrmex caledonica Andre 1889E14
  Sphecomyrmodes occidentalis Perrichot, Nel et al. 2007V10
  LabidusB10
    |--L. coecusRC79
    |--L. latreillii [=Dorylus (Labidus) latreillii]G20
    `--L. praedatorB10
  Eusphinctus Emery 1893TB85
  Chalepoxenus muellerianusES12
  Cretacoformica explicata Jell & Duncan 1986Z01
  Formicium giganteumS12
  Eomyrmex Hong 1974H02
    `--E. guchengziensis Hong et al. 1974P92
  Aeromyrma sophiae Emery 1890H02
  ArchaeoponeP92
  ArmaniellaP92
  CretoponeP92
  DolichomyrmaP92
  PetroponeP92
  PoneropterusP92
  PseudarmaniaP92
  AsymphylomyrmexP92
  BradoponeraP92
  ElectromyrmexP92
  ElectroponeraP92
  EnneamerusP92
  MonoriscusP92
  NothomyrmicaP92
  ParameranoplusP92
  ParaneuretusP92
  PronolepisP92
  ProtaneuretusP92
  RhopalomyrmexP92
  StigmomyrmexP92
  StiphromyrmexP92
  HypopomyrmexP92
  Ilemomyrmex caecusP92
  Oxyidris antillanaP92
  ParacryptocerusP92
  OctostrumaP92

*Type species of generic name indicated

References

Archibald, S. B., K. R. Johnson, K. W. Mathewes & D. R. Greenwood. 2011. Intercontinental dispersal of giant thermophilic ants across the Arctic during early Eocene hyperthermals. Proceedings of the Royal Society of London Series B—Biological Sciences 278 (1725): 3679–3686.

[A71] Askew, R. R. 1971. Parasitic Insects. Heinemann Educational Books: London.

[B03] Bingham, C. T. 1903. The Fauna of British India, including Ceylon and Burma. Hymenoptera vol. 2. Ants and Cuckoo-Wasps. Taylor and Francis: London.

[BS06] Brady, S. G., T. R. Schultz, B. L. Fisher & P. S. Ward. 2006. Evaluating alternative hypotheses for the early evolution and diversification of ants. Proceedings of the National Academy of Sciences of the USA 103 (48): 18172–18177.

[B10] Brown, B. V. 2010. Phoridae (hump-backed flies, scuttle flies). In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado (eds) Manual of Central American Diptera vol. 2 pp. 725–761. NRC Research Press: Ottawa.

Dlussky, G. M. 1999. The first find of the Formicoidea (Hymenoptera) from the lower Cretaceous of the Northern Hemisphere. Paleontologicheskii Zhurnal 1999 (3): 62–66 (translated: Paleontological Journal 33 (3): 274–277).

[E89a] Emery, C. 1889a. Intorno ad alcune formiche della fauna palearctica. Annali del Museo Civico di Storia Naturale di Genova, Serie 2a, 7: 439–443.

[E89b] Emery, C. 1889b. Viaggio di Leonardo Fea in Birmania e regioni vicine. XX.—Formiche di Birmania e del Tenasserim raccolte da Leonardo Fea (1885–87). Annali del Museo Civico di Storia Naturale di Genova, Serie 2a, 7: 485–520.

[E14] Emery, C. 1914. Les fourmis de la Nouvelle-Calédonie & des îles Loyalty. In: Sarasin, F., & J. Roux (eds) Nova Caledonia: Forschungen in Neu-Caledonian und auf den Loyalty-Inseln. A. Zoologie vol. 1 pt 4 pp. 393–436, pl. 12. C. W. Kreidels Verlag: Wiesbaden.

[ES12] Espadaler, X., & S. Santamaria. 2012. Ecto- and endoparasitic fungi on ants from the Holarctic region. Psyche 2012: 168478.

[FT08] Framenau, V. W., & M. L. Thomas. 2008. Ants (Hymenoptera: Formicidae) of Christmas Island (Indian Ocean): identification and distribution. Records of the Western Australian Museum 25 (1): 45–85.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[GE05] Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

[H82] Helmore, D. W. 1982. Drawings of New Zealand insects. Bulletin of the Entomological Society of New Zealand 8: 1–52.

[H02] Hong Y. 2002. Amber Insect of China. Beijing Scientific and Technological Publishing House.

[I92] Iwahashi, J. (ed.) 1992. Reddo Deeta Animaruzu: a pictorial of Japanese fauna facing extinction. JICC: Tokyo.

[P92] Poinar, G. O., Jr. 1992. Life in Amber. Stanford University Press: Stanford.

[RBV08] Rabeling, C., J. M. Brown & M. Verhaagh. 2008. Newly discovered sister lineage sheds light on early ant evolution. Proceedings of the National Academy of Sciences of the USA 105 (39): 14913–14917.

[RC79] Ross, L. J., & E. A. Cross. 1979. A revision of the genus Acinogaster (Acari: Pygmephoridae). International Journal of Acarology 5 (3): 231–250.

[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.

[S12] Schaal, S. 2012. Messel Pit fossil site—the legacy of the environment and life of the Eocene. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 225–236. Springer.

[TB85] Taylor, R. W., & D. R. Brown. 1985. Formicoidea. In: Walton, D. W. (ed.) Zoological Catalogue of Australia vol. 2. Hymenoptera: Formicoidea, Vespoidea and Sphecoidea pp. 1–149. Australian Government Publishing Service: Canberra.

[V10] Vršanský, P. 2010. Cockroach as the earliest eusocial animal. Acta Geologica Sinica (English Edition) 84 (4): 793–808.

[WB03] Ward, P. S., & S. G. Brady. 2003. Phylogeny and biogeography of the ant subfamily Myrmeciinae (Hymenoptera: Formicidae). Invertebrate Systematics 17: 361–386.

[WW90] Wheeler, G. C., & J. Wheeler. 1990. Insecta: Hymenoptera Formicidae. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 1277–1294. John Wiley & Sones: New York.

Wilson, E. O. 1987. The earliest known ants: an analysis of the Cretaceous species and an inference concerning their social organization. Paleobiology 13 (1): 44–53.

[Z01] Zhou, S. 2001. Ants of Guangxi. Guangxi Normal University Press: Guilin (China).

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