Melissotarsus

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Melissotarsus
Temporal range: 23–0 Ma
Early Miocene – Recent
Melissotarsus beccarii
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Melissotarsus
Emery, 1877
Type species
Melissotarsus beccarii
Diversity
4 species
1 fossil species
(Species Checklist)

Melissotarsus beccarii casent0102042 profile 1.jpg

Melissotarsus beccarii

Melissotarsus beccarii casent0102042 dorsal 1.jpg

Specimen Label

Evolutionary Relationships

Rostromyrmex






Cardiocondyla



Ocymyrmex






Nesomyrmex



Xenomyrmex





Terataner




Atopomyrmex



Cataulacus










Carebara



Diplomorium






Melissotarsus



Rhopalomastix






Calyptomyrmex



Tetramorium





Cyphoidris



Dicroaspis










Aretidris



Vollenhovia





Dacetinops



Indomyrma








Crematogaster



Meranoplus






Lophomyrmex




Adlerzia



Recurvidris






Stereomyrmex




Trichomyrmex





Eutetramorium




Royidris




Malagidris



Vitsika








Huberia



Podomyrma





Liomyrmex



Metapone













Kartidris



Mayriella





Tetheamyrma




Dacatria



Proatta









Dilobocondyla



Secostruma






Acanthomyrmex



Myrmecina





Perissomyrmex



Pristomyrmex









some Lordomyrma



Propodilobus





Lasiomyrma




[some Lordomyrma




Ancyridris



some Lordomyrma









Paratopula




Poecilomyrma




Romblonella



Rotastruma








Gauromyrmex



Vombisidris





Temnothorax




Harpagoxenus



Formicoxenus



Leptothorax













Based on Ward et al. (2014) and Blaimer et al. (2018).

Existing literature on all four species of Melissotarsus reveals similar habits of relying on diaspidid scale insects for food within the confines of galleries chewed in healthy wood. The ants' anomalous morphology (head and legs) represents extreme adaptations (tunnelling through live wood and silk spinning) for their obligate mutualism with diaspidid scale insects. Unlike other symbiotic associations between ants and scale insects, honeydew is not the currency of exchange for Melissotarsus. Indeed, armoured scale insects (Diaspididae) do not produce honeydew (Beardsley & Gonzalez 1975). In addition to gaining access to underlying meristem tissue, diaspidids benefit from highly effective protection (enemies and weather) by the ants. Accordingly, they stop building their trademark shields even though they continue secreting wax and proteins as construction material. These secretions, together with exuviae and anal excretions, can provide an adequate array of nutrients for the ants. Furthermore, ants can also feed on dead or dying diaspidids (Peeters et al. 2017). Claims that the ants use diaspidids as 'domestic cattle' (Schneider et al. 2013) are revisited by Peeters et al. (2017).

Save for brief periods of sexual activity and colony founding by queens, Melissotarsus ants live in splendid isolation from the outside world. Accordingly they are poorly known, even though they appear widespread throughout Africa and Madagascar.

Silk-producing glands are present in the head of adult workers (a trait unique to the genus), and silk is spun and combined with wood particles to seal cracks in tunnel walls (Fisher & Robertson 1999). Workers cannot forage outside the wood because the second pair of legs project upward, a novel adaptation for locomotion along the galleries (Delage-Darchen 1972).

Chambers dug beneath the bark by ants, containing symbiotic coccoids and scattered ant larvae. From northern Mozambique. Photos by Christian Peeters.
Melisso coccoids&ants Peeters.jpg
Melisso emeryi coccoids Peeters.jpg
Aggregation of naked diaspidids, together with two rare shields (on right). The latter is evidence that the secretory glands of ant-associated Morganella conspicua continue to be functional. Photos by Christian Peeters.

Hita Garcia, Wiesel and Fischer (2013) - The four species of this Afrotropical and Malagasy genus are rarely encountered. The Afrotropical species were revised by Bolton (1982) who also provided a good species identification key. These ants are special in several ways. They build their nests in healthy wood by tunnelling through the living tissue beneath the surface (Bolton, 1982; Fisher & Robertson, 1999; Belshaw & Bolton, 1994) and are rarely found outside of their nests, which could be the main reason for their relative scarcity in museum collections (Bolton, 1982). They live in close association with symbiotic coccids that are kept inside the nest. Adults are able to produce silk, which is used to close exit holes or to seal cracks (Fisher & Robertson, 1999).


Identification

Bolton (1982) - Myrmicine ants with moderate to conspicuous size variation in most nest samples, living under bark and in wood of live trees. Mandibles short, when unworn armed with a long finger-like apical tooth followed by two much smaller teeth and sometimes also by a minute basal denticle. With wear these gradually become an undifferentiated blunt margin. Palp formula 0,1 (weissi). Median portion of clypeus bluntly triangular in shape and somewhat raised, not projecting back between the frontal lobes. Lateral portions of clypeus simple and unmodified. Frontal lobes narrow, confluent centrally and separated only by a narrow impressed line; the anteriormost parts of the frontal lobes abut the posterior clypeal margin. Antennal scrobes absent. Frontal carinae absent. Antennae with six segments, the scapes very short (SI 39-47), the two apical segments forming a strong club. Eyes present, distinctly longer than broad and set in front of the midlength of the sides. Alitrunk short, fusiform and box-like, without dorsal sutures or impressions except in the very largest individuals where rarely a metanotal impression is shallowly present. Propodeum unarmed and rounded. Metapleural lobes absent. Lateral portions of pronotum reduced to a narrow V -shaped wedge below the level of the conspicuous mesothoracic spiracle. Anterior coxae small, much smaller than the massively developed middle and hind coxae. Propodeal spiracle round, situated low on the side of the propodeum and just behind its mid length. Metapleural gland system easily visible through the cuticle. Basitarsal segment of each leg greatly swollen, as wide as the preceding tibia, terminating apically in a circlet of small teeth on the anterior (leading) edge on the middle and hind basi tarsi. Petiole with an anterior peduncle and a small low posteriorly situated node which is broadly attached to the postpetiole; the latter broadly attached to the gaster. Dorsal alitrunk finely longitudinally costulate throughout. Elongate fine hairs present dorsally on head and body, and also present on the upper surfaces of the scapes and outer surfaces of the tibiae.

The genus most closely related to Melissotarsus is Rhopalomastix Forel, represented by three or four poorly defined species distributed throughout the Oriental and Indo-Australian zoogeographical regions and utilizing the same lifeway as Melissotarsus. Since Emery (1922a) and Wheeler (1922) produced their classifications these two small genera have always been placed together in a tribe of their own (Melissotarsini) and it is fairly certain that they represent two stages on a single adaptive line. Rhopalomastix is the more generalized of the two, Melissotarsus decidedly the more specialized, but the modifications seen in the latter are foreshadowed in the former genus. It is the accentuation of these adaptive specializations which separates the genera, as follows.

Rhopalomastix

Antennae 10-segmented. Lateral portion of pronotum extensive, distinctly larger than the mesopleuron. First coxa as large as or larger than the second and third coxae. Petiole sub-sessile, with a strong ventral process. Free posterior face of petiole node long, its articulation with the postpetiole narrow. Basitarsal segment of each leg not swollen, without apical circlets of teeth. Sting long and strong.

Melissotarsus

Antennae 6-segmented. Lateral portion of pronotum very reduced, forming a V-shaped narrow wedge which is smaller than the mesopleuron. First coxa much smaller than the swollen second and third coxae. Petiole short-pedunculate, with feeble or no ventral process. Free posterior face of petiole node very short, its articulation with the postpetiole very broad. Basitarsal segment of each leg strongly swollen, with apical circlets of teeth. Sting very reduced and probably non-functional.

Keys to Species in this Genus

Distribution

World distribution based on political regions. View/Edit Data
Melissotarsus Distribution.png Worlddistribution legend.jpg

Species richness

Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data

Melissotarsus Species Richness.png

Biology

Bolton (1982) - This small genus, of which only four uncommon species are presently recognized, is restricted to the Malagasy region (1 species) where it is rare, and the Afrotropical region (3 species) where it is, however, very widespread. The species nest in the healthy wood of living trees, apparently tunnelling their own galleries below the surface. For this reason most collections of Melissotarsus are made more by luck than by intent as their presence in the wood is usually not detectable on the surface. Delage-Darchen (1972) has shown that the method of walking in these ants is very strange; they progress on their front and hind legs with the middle pair projecting upwards, and presumably in contact with the gallery roof. She also noted the presence of coccids inside the galleries, also discussed by Ben-Dov (1978). It seems probable that coccid secretions form a major, if not the main, item in the diet of Melissotarsus species.

Castes

Winged queens and workers differ little in body size. However reproductive queens become physogastric as a result of highly active ovaries.

Worker, delate queen and males of Melissotarsus. From Gorongosa, Mozambique. Photo by Adam Khalife.
Physogastric queen of Melissotarsus, i.e. abdomen is greatly enlarged by stretching the intersegmental membranes. From Toamasina Province, Madagascar. Photo by Christian Peeters

Morphology

Worker Morphology

 • Antennal segment count 6 • Antennal club 2 • Palp formula 0,1 • Total dental count 1-4 • Spur formula 0, 0 • Sting present

Male Morphology

 • Antennal segment count 11-12 • Antennal club 0 • Palp formula 0,1 • Total dental count 0-2 • Spur formula 0, 0

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • MELISSOTARSUS [Myrmicinae: Melissotarsini]
    • Melissotarsus Emery, 1877b: 378. Type-species: Melissotarsus beccarii, by monotypy.

References