Gesomyrmex

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Gesomyrmex
Temporal range: 48.6–0 Ma Eocene – Recent
Gesomyrmex chaperi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Gesomyrmecini
Genus: Gesomyrmex
Mayr, 1868
Type species
Gesomyrmex hoernesi
Diversity
7 species
11 fossil species
(Species Checklist, Species by Country)

Gesomyrmex-luzonensisLM4.jpg

Gesomyrmex chaperi

Gesomyrmex luzonensis, worker, head.jpg

Specimen Label

Synonyms
Evolutionary Relationships
Formicinae

Myrmelachistini
  (2 genera)




Lasiini
  (11 genera)




Melophorini
  (9 genera)




Formicini
  (8 genera)






Gesomyrmex
  (7 species)



Oecophylla
  (15 species)




Plagiolepidini
  (9 genera)





Gigantiops, Myrmoteras, Santschiella



Camponotini
  (8 genera)








Based on Ward et al. 2016.


A poorly known resident of tree canopies in Oriental tropics, showing a striking diversity of caste morphologies. Queens and supersoldiers share an elongate head with powerful mandibles, an adaptation to chew an entrance tunnel to the innermost pith of living branches (Peeters et al. 2017).


Photo Gallery

  • Gesomyrmex chaperi worker from Vietnam
  • Supersoldier, soldier, workers and brood of Gesomyrmex sp. From Danum, Sabah. Photo © Christopher Wilson.
  • Two size classes of Gesomyrmex sp. soldiers (above), and workers (Sabah colony). Pupae are naked (Wheeler 1923a), thus cocoons have been lost as in Oecophylla. Photo by Christopher Wilson.
  • Gesomyrmex sp. from Baltic amber. Photo by Levon Biss.
  • A Baltic amber fossil.

Identification

Workers of the genus are easily recognised by the following features: elongated compound eyes; antennal scape passing below the eye; masticatory margin of mandible with more than four teeth (Bolton, 1994). The workers have 8-jointed antennae and soldiers of Gesomyrmex chaperi have 9-jointed antennae (Wheeler, 1916), whereas females have 10-jointed antennae Dubovikov (2004).

Gary Alpert is of the opinion that all described species belong to Gesomyrmex chaperi (the name with priority). Caste polymorphism has led to great taxonomic confusion, both in extant and fossil species. Marked colour variations further complicate alpha taxonomy. Wheeler (1929) already suggested that extant species may correspond to “sub-species or varieties”.

The genus is similar to Santschiella: two very large eyes, widely separated antennal insertions, and scapes that pass below the eyes.

AntWeb icon 02.png See images of species within this genus

 

Distribution

Distribution and Richness based on AntMaps

Fossils

Fossils are known from: Baltic amber (Bartonian, Middle to Late Eocene), Bitterfeld amber (Bartonian, Middle to Late Eocene), Bol’shaya Svetlovodnaya, Sikhote-Alin, Russia (Priabonian, Late Eocene), Danish-Scandinavian amber (Bartonian, Middle to Late Eocene), Eckfeld, Germany (Lutetian, Middle Eocene), Messel, Germany (Lutetian, Middle Eocene), Oise amber, France (Ypresian, Early Eocene), Radoboj, Croatia (Burdigalian, Early Miocene), Rovno amber (Priabonian, Late Eocene).

Biology

From Peeters et al. (2017) Gesomyrmex chaperi presents an intriguing division of labour: workers are the active hunters, with very distinct mandibles. Queens (as well as two kinds of soldiers) have different mandibles, indicating that they do not hunt during colony foundation. However, a foundress needs to chew an entrance tunnel through living wood, and then block this nest entrance for many months until the colony is strong enough to produce the first soldiers. Supersoldiers are presumably reared even later in colony ontogeny, because they are more costly. Relatively few supersoldiers are present and they show two queen-like behaviours: they stay inside nest chambers and block the entrances, and they chew entrance holes when starting other nests belonging to the same colony. Supersoldiers also store nutrients (trophic eggs) in their gaster.

Gesomyrmex nest entrance. Photo by Decha Wiwatwitaya
Gesomyrmex nest in the very center of the heartwood in living branches of small diameter. Photo by Decha Wiwatwitaya
To access this secure innermost pith, the founding queen needs to chew an entrance tunnel. Photo by Decha Wiwatwitaya
Supersoldier head blocking the entrance. Photo by Decha Wiwatwitaya

Dubovikov (2004) - Members of this genus are very rare and ancient forms. The population of their nests are small and they live in small branches of trees (Cole, 1949b). Identification key to five living Gesomyrmex species was published by Cole (1949a).

Life History Traits

  • Mean colony size: ~150 (Greer et al., 2021)
  • Compound colony type: not parasitic (Greer et al., 2021)
  • Nest site: arboreal (Greer et al., 2021)
  • Diet class: omnivore (Greer et al., 2021)
  • Foraging stratum: arboreal (Greer et al., 2021)

Castes

In addition to winged queens, three sterile castes can be distinguished using discrete morphological traits, morphometry and total body size (Peeters et al. 2017). Observations of behaviour are challenging in tree canopies, and functional morphology can be used to predict the specialised functions of different castes.


Heads of all four castes of Gesomyrmex sp. shown at different scales (A: worker, B: soldier, C: supersoldier (all from Sabah colony); D: queen from Ulu Gombak). Note differences in ocelli, clypeus, mandibles and frontal lobes (covering the antennal sockets). Photo by Mônica Antunes Ulysséa

Morphology

Worker Morphology

• Antennal segment count: 8 in worker, 10 in queen • Antennal club: gradual • Palp formula: 6,4 • Total dental count: 6-10 • Spur formula: 1 simple, 1 simple; 0,0 • Eyes: >100 ommatidia • Scrobes: absent • Pronotal Spines: absent • Mesonotal Spines: absent • Propodeal Spines: absent • Petiolar Spines: absent • Caste: polymorphic • Sting: absent • Metaplural Gland: present • Cocoon: absent

Male Morphology

 • Antennal segment count 11 • Antennal club 0 • Palp formula 6,4 • Total dental count 1 • Notes: from literature

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • GESOMYRMEX [Formicinae: Gesomyrmecini]
    • Gesomyrmex Mayr, 1868c: 50. Type-species: †Gesomyrmex hoernesi, by monotypy.
    • Gesomyrmex senior synonym of Gaesomyrmex: Forel, 1893a: 167.
    • Gesomyrmex senior synonym of Dimorphomyrmex: Wheeler, W.M. 1929a: 1.
  • DIMORPHOMYRMEX [junior synonym of Gesomyrmex]
    • Dimorphomyrmex André, 1892b: 49. Type-species: Dimorphomyrmex janeti (junior synonym of Gesomyrmex chaperi), by monotypy.
    • Dimorphomyrmex junior synonym of Gesomyrmex: Wheeler, W.M. 1929a: 1.
  • GAESOMYRMEX [junior synonym of Gesomyrmex]
    • Gaesomyrmex Dalla Torre, 1893: 175, unjustified emendation of Gesomyrmex.
    • Gaesomyrmex junior synonym of Gesomyrmex: Forel, 1893a: 167.

Dubovikov (2004) - The genus Gesomyrmex was established by G. Mayr (1868) for a single species from Baltic amber (Lower Oligocene). The four extant species (Gesomyrmex chaperi, Gesomyrmex howardi, Gesomyrmex kalshoveni and Gesomyrmex spatulatus) are known only from workers. Gesomyrmex luzonensis and Gesomyrmex tobiasi were described from lone queens.

Ward et al. (2016) - The tribe Gesomyrmecini is here restricted to Gesomyrmex and two similar fossil taxa (Wheeler 1915). Bolton (2003) also placed Santschiella in Gesomyrmecini, but the molecular results do not support a close relationship between Gesomyrmex and Santschiella (Blaimer et al. 2015). The similarities between the two—very large eyes, widely separated antennal insertions, and scapes that pass below the eyes (Bolton 2003)-must be interpreted as due to convergence.

References

35 – 40.
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