Odontomachus bauri

A widespread and highly variable species.

Identification
Key to Odontomachus of the New World

Distribution based on Regional Taxon Lists
Neotropical Region: Barbados, Bolivia, Brazil, Colombia, Costa Rica, Dominican Republic, Ecuador, Galapagos Islands, Greater Antilles, Haiti, Honduras, Mexico, Panama, Paraguay, Peru, Puerto Rico, Saint Lucia, Trinidad and Tobago, Venezuela.

Biology
Ehmer and Holldobler (1998) provided the following details about this species in a study from Barro Colorado Island in Panama (the text has been edited and in some case summarized):

Foraging behavior

Foragers were active at all times of the day. Odontomachus bauri is a leaf litter ant and forages individually most of the time underneath the leaf litter. It probes narrow crannies for arthropods, and also readily takes dead insects. It was repeatedly observed that individual workers appear to return to locations where they had previously found food...The foraging success of Odontomachus bauri, as determined by the proportion of workers returning with prey, is at least 28% (n=325). 41% of incoming workers were definitely unsuccessful as they entered the nest with opened mandibles, and the remaining 31% had either no prey or prey which was too small to be discerned.

O. bauri accepts a wide range of invertebrates, but forages especially frequently on other ants and termites. The termites captured were mainly workers (22 of 25 caught were workers, 3 were soldiers). The termites all belonged to the family Termitidae: most were Nasutitermes; the rest were Amitermes. The ant prey consisted mainly of sexuals. The largest prey items are most likely found dead and then carried to the nest. The successful capture of larger insects was not observed, but the detection and retrieval of dead items was repeatedly witnessed. The size distribution of the prey specimens shows that items between 3 mm and 4 mm are the most common size class and the most frequent prey items, like termites and wood lice, are soft bodied.

Foraging area and polydomy

Colonies establish foraging territories and tend to avoid conspecific territories of neighboring nests. No queens were found in 9 colonies excavated at Gigante, but all nests contained larvae and pupae. All of these nests did not extend into the soil, they consisted of gaps and cavities in leaf litter and under wood. Nests were also commonly found in the accumulated leaf litter in the tops of Elaeis palms more than 2 m tall. Five of 9 colonies in palms tops contained single queens. It seems that colonies of O. bauri are monogynous and sometimes polydomous in this habitat.

Significance of the trap-jaws

In O. bauri, the trap-jaws appear to be designed to stun or kill prey, usually small, soft-bodied insects. This is suggested by the fact that O. bauri has short, broad mandibles with blunt instead of sharp teeth (Brown, 1976). The function of the mandibles is especially evident when the ants were observed catching termites. The ants snapped at individual termites and either stunned or squashed the insects. Even though the prey was usually stunned by the first strike, often the ant administered repeated blows before carrying the prey to the nest. O. bauri never stung termite prey, as was regularly observed in Ectatomma ruidum. Use of the high speed mandible strike may also be an effective mechanism for avoiding the chemical defenses by arthropods like the termite Nasutitermes. The very high speed of closure of the mandibles, and the fast release of the reflex via range finding trigger hairs (Gronenberg et al., 1993; Gronenberg, 1995), as well as the "strike and recoil" behavior, should be very well suited to handle chemically protected prey (Brown, 1976). Indeed, Traniello (1981) found that O. bauri was the most efficient ant species tested at successfully attacking Nasutitermes soldiers, which squirt a secretion that entangles and irritates an aggressor and can physically block sensilla and spiracles (Prestwich, 1979). The presence of Nasutitermes workers among prey items retrieved by O. bauri workers in this study shows that O. bauri can exploit a food resource largely unavailable to other ants.

Oliveira and Holldobler (1989) studied details of this ant's foraging behavior and found they use visual cues, including canopy pattern, as a means of home orientation/navigating. It was also found that workers are able to transmit recruitment signals, likely via the means of chemicals and antennal contact. It appears the cues elicts more of a stimulation response rather than guiding other foragers directly to rich food finds.

Brown (1976) provided the following synopsis regarding the distribution of and variation within this species:

Odontomachus bauri is a very widespread and variable species that usually has been lumped with Odontomachus haematodus. Of many sculptural variants, we can sort out one major trend toward coarser sculpture, particularly in the striation of the petiolar node, in samples from moist forest in continental South and Central America, while samples from the llanos and semi desert areas of Venezuela, Colombia and adjacent areas tend to have finer sculpture, with the petiolar node being delicately striate or striate-reticulate. The continental wet forest populations also tend in many cases to be larger, darker, more robust, and to have a thicker, more dome-shaped petiolar node in the worker.

O. bauri extends southward through Colombia and Ecuador on both sides of the Andes, and on the Pacific side it probably reaches south as far as real lowland or foothills forest does — possibly into Peru. In western Colombia and Ecuador, it is the dominant species of the genus, and is not accompanied here by O. haematodus, but only locally by Odontomachus erythrocephalus among closely related species (haematodus group; the much smaller and more cryptic Odontomachus minutus occurs on the Pacific side in wet forest, and Odontomachus brunneus may extend here also, but these are probably not serious competitors). Even on Barro Colorado Island in the Canal Zone, O. bauri is the most commonly collected, and probably dominant, species of the genus, though 5 or 6 congeners co-occur there. The Galapagos populations, which furnished the type of bauri, probably arose from Ecuadorean propagules, perhaps transported the islands accidentally by man.

The llanos populations extend through the Orinoco Delta (where they previously were mistakenly regarded by me as intergrades between bauri and haematodus) and Trinidad (the Odontomachus sericeus of Provancher), from that island extending into the Antilles as far as Hispaniola and Jamaica, but not Cuba or the Bahamas. Formica unispinosa Fabricius, described from Guadeloupe and long regarded as a synonym of O. haematodus, may be the same as bauri. Since at least O. brunneus also is widespread in the Lesser Antilles, the identity of unispinosus remains in some doubt, and it seems best to regard it as a nomen oblitum, which it is under the Code.

Roger's variety pubescens of Odontomachus haematodus in the old sense, from La Guaira, Venezuela, is possibly another early name for bauri, here rejected for similar reasons. A vigorous search for type material of var. pubescens in MNK-Berlin and elsewhere in European museums has proven fruitless, and the name is best placed in the oblitum category.

The West Indian bauri are even more variable than the mainland populations, and they tend to be smaller and with less dome-shaped petiolar nodes; the legs are often partly or entirely reddish or yellow in color.

The Hispaniolan form, which my wife and I collected widely in the Dominican Republic, especially in the pine-covered mountains of the southwestern and central parts of the country, and which is widespread in Haiti (MCZ), approaches black in color, but has the coxae and part of the femora contrasting brownish orange. In the Samana Peninsula and some drier parts of the island, the color is lighter, especially the brown trunk, and the legs tend to be all yellow. The form from Hispaniola corresponds to Emery's var. paucidens. A dark brown, slender variant with yellowish legs, superficially very like the typical O. haematodus, inhabits Jamaica and Mona Island. From Puerto Rico the samples available vary somewhat (var. notatus) but are basically brown, usually with the trunk — or at least the propodeum — and the petiole lighter and more reddish. The legs are yellowish to dull orange, at least over the coxae and basal half of femora. Many of the lighter specimens are in old museum lots, whereas the series we took in the Dominican Republic in 1975 are all blackish, mostly with blue iridescent reflections on the mesopleura, and have the orange leg bases rather brightly contrasting, indicating that fading may be important in older preserved specimens of Antillean samples.

South of the llanos, O. bauri is widespread in the Amazon Basin and the lower eastern foothills of the Andes up to at least 1000 m in Peru. It reaches the mouth of the Amazon near Belem, in the east, and extends southward through the forests of northern Mato Grosso and beyond into more open country. In most of Amazonia, it is less common than O. haematodus. The southern limits of O. bauri are not well known, due to its previous confusion with other species, but it has been collected at several localities in western Sao Paulo State by Karol Lenko, including Ilha Solteira in the Rio Parana. The MCZ has a sample taken at Buriti, near Cuiaba in central Mato Grosso (R. Duffield leg.), and an alate queen from Quincemil (750 m) in SE Peru. I regard it as certain that O. bauri extends well into Bolivia, but I have seen no specimens from that country yet. It also is found in dry northeastern Brasil, in Ceara and Paraiba.

Although bauri is common in Panama and around the Oolfo Dulce in SW Costa Rica, it is less common in northern Costa Rica. I took an alate queen near Ouapiles, in northern Limon Province, so the species may well reach into the Nicaraguan lowlands, but I have seen no specimens of bauri from Nicaragua or countries to the north, where Odontomachus laticeps prevails.

Nomenclature

 * pubescens. Odontomachus haematodus var. pubescens Roger, 1861a: 25 (w.) VENEZUELA. Forel, 1909a: 252 (q.). Raised to species: Dalla Torre, 1893: 52. Subspecies of haematodus: Emery, 1890b: 44 (footnote); Emery, 1911d: 115. Junior synonym of bauri: Brown, 1976a: 102.
 * microcephalus. Odontomachus haematodes var. microcephalus Emery, 1890b: 45, pl. 5, fig. 1 (w.) COSTA RICA. [Also described as new by Emery, 1894k: 50.] Junior synonym of bauri: Brown, 1976a: 102.
 *  bauri. Odontomachus bauri Emery, 1892d: 561 (diagnosis in key) (w.) ECUADOR (Galapagos Is). Emery, 1893d: 90 (w.); Wheeler, W.M. 1919c: 267 (q.m.). Subspecies of haematodus: Emery, 1911d: 115. Revived status as species: Taylor & Wilson, 1962: 142. Senior synonym of microcephalus, notata, paucidens, pubescens, rugisquama, sericeus: Brown, 1976a: 102. See also: Brown, 1976a: 129.
 * paucidens. Odontomachus haematodus var. paucidens Emery, 1893d: 91 (footnote) (w.) HAITI. Menozzi & Russo, 1930: 151 (m.). Subspecies of haematodus: Wheeler, W.M. 1936b: 196. Junior synonym of bauri: Brown, 1976a: 102.
 * sericeus. Odontomachus sericeus Provancher, 1895: 97 (q.) TRINIDAD. Junior synonym of bauri: Brown, 1976a: 102.
 * rugisquama. Odontomachus haematodes var. rugisquama Forel, 1908b: 35 (w.) COSTA RICA. Forel, 1912c: 28 (q.). Junior synonym of bauri: Brown, 1976a: 102.
 * notata. Odontomachus haematoda var. notata Mann, 1920: 404 (w.) PUERTO RICO. Junior synonym of bauri: Brown, 1976a: 102.

Wheeler (1919)

Description
Worker. Length 9-11 mm.

Differing from the worker of the typical form in having the head proportionally narrower behind, slightly narrower mandibles, with longer preapical tooth, the smooth, shining portion of the occiput extending somewhat further forward and that of the sides of the head further dorsally. The longitudinal striae of the pronotum and transverse striae of the epinotum are somewhat coarser and the anterior surface of the petiole is rather coarsely, transversely striate. The pilosity, pubescence and color are much as in the typical haematoda, but the body has a somewhat bronzy lustre and the antennae and legs are darker.

Queen
Length 10-11 mm.

Very similar to the worker and differing from the female of the typical haematoda in the same characters. The wings measure only 7 mm, or somewhat less, however, whereas those of the typical haematoda measure at least 8 mm.

Male
Length 6 mm.

Closely resembling the male of the typical haematoda, except in color. The head, thorax, legs and antennae are whitish yellow, with the epinotum, petiole and dorsal surface of the gaster dark brown, the venter brownish yellow. The mesonotum has a dark brown longitudinal spot on each side and a slightly paler median spot of the same color just behind its anterior border. Wings whitish, with pale brown stigma.

This form, which is extremely close to the typical haematoda, so widely distributed in the tropics of both hemispheres, was described by Emery from a single worker taken by Dr. G. Haur on Chatham Island. I have redescribcd it from a number of workers and females and a single male taken by Dr. F. X. Williams on the same island and at Cormorant Bay, Charles Island. The specimens were nesting under stones from sea-level to an altitude of 1100 feet.