Melissotarsus emeryi

Thousands of workers and several dealate queens nest under the bark of trees, after tunneling galleries in live wood. They obtain all nourishment from armoured scale insects (Diaspididae). Ants are never active outside trees, except for sexuals exiting the nest for mating and colony foundation.

Studied in South Africa by Prins et al. (1975), Ben-Dov & Fisher (2010), Schneider et al. (2013). Studied in Mozambique by Peeters et al. (2017)



Identification
This species can be identified by the abrupt anterior edge of the pronotum in dorsal and lateral view. Some individuals seem intermediate between those of emeryi and those of Melissotarsus beccarii, and in consequence are difficult to place.

1)

-With the alitrunk in dorsal view the anterior margin of the pronotum rounding evenly into the anterior declivity, the two not meeting in a sharp angle or edge. (Ethiopia, Tanzania, South Africa, Ivory Coast). . . . . beccarii

-With the alitrunk in dorsal view the anterior margin ofthe pronotum separated from the anterior declivity by a sharp angle or edge. . . . . 2

2)

-Sides of alitrunk meeting dorsum in a fairly well-defined angle. Alitrunk colour medium to dark reddish brown. (Ghana, Congo, Zaire). . . . . weissi

-Sides of alitrunk rounding bluntly into the dorsum. Alitrunk colour yellow to light yellowish brown. (Ethiopia, Sudan, Kenya, Tanzania, Zaire, Central African Republic. South Africa, Ivory Coast, Ghana). . . . . emeryi

Distribution based on Regional Taxon Lists
Afrotropical Region: Central African Republic, Democratic Republic of Congo, Ethiopia, Ghana, Kenya, Mozambique, Saudi Arabia, Senegal, South Africa, Sudan, Zambia.

Biology
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).

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.

Nomenclature

 *  emeryi. Melissotarsus emeryi Forel, 1907c: 133 (w.) ETHIOPIA. Bolton, 1982: 335 (m.). Senior synonym of compressus, pilipes: Bolton, 1982: 337.
 * pilipes. Melissotarsus emeryi var. pilipes Santschi, 1914b: 71 (w.) KENYA. Junior synonym of emeryi: Bolton, 1982: 337.
 * compressus. Melissotarsus compressus Weber, 1952: 1, figs. 28, 29 (q.) CENTRAL AFRICAN REPUBLIC. Junior synonym of emeryi: Bolton, 1982: 337.

Bolton (1982) - So little material of Melissotarsus is available at present that this survey must be regarded as strictly preliminary. Three species are now recognized in the Afrotropical region but it is possible that each may be compounded of more than one different sibling-species. Conversely it is by no means impossible that further collections will bridge what appear here as species for the differences between them, though consistent in the few samples to hand, are relatively minor and may well be anulled by further collecting.

The three presently recognised species are basically so similar that to present a full description for each would be redundant so, for the purposes of identification, a description of the type-species beccarii is given and the other two are compared to it.

The shape of the alitrunk in dorsal view shows subtle but perhaps significant differences between separate series of workers presently grouped as single species, but discovering whether these differences are meaningful, or even consistent, will have to await the amassing of considerably more samples than are presently available.

M. emeryi and beccarii have pale yellow feebly sclerotized males, and have females in which the postpetiole in dorsal view is quite broad (1.90-2.20 x broader than long) and lacking a rounded anterior margin, the margin instead being more or less straight or even slightly concave. The workers are yellow to light yellowish brown and have the sides of the alitrunk rounding bluntly into the dorsum when seen in dorsal view. Females of emeryi differ from those of beccarii as in the former the mesoscutum is broader than long in dorsal view; it is longer than broad in the latter. Workers of emeryi have the anterior margin of the pronotum sharply defined and angular where it meets the anterior declivity, whereas in beccarii there is no such sharp differentiation between dorsum and anterior declivity, instead the one surface rounds bluntly into the other.

Worker
Bolton (1982) - TL 2.5-3.4, HL 0.66-0.88, HW 0.70-0.90, CI 100-105, SL 0.30-0.38, SI 39-43, PW 0.37-0.57, AL 0.62-0.88 (13 measured).

Answering to the description of Melissotarsus beccarii but with the anterior pronotal margin in dorsal view separated from the anterior declivity by a well defined angle or edge.