Nothomyrmecia macrops

This ant was a myrmecological mystery for many decades after its description in 1934. The original type specimens were the only samples collected until the ant was rediscovered in the 1970s. Besides some vague locality data and Clark's statement about a 2,500 km stretch of southern Australia: "beyond those collected by Miss Baesjou very few species of ants have been seen from the great stretch of country lying between Albany, Western Australia, and Port Lincoln, South Australia" it was not clear where the types were even found. Taylor (1978) was finally able to report - Nothomyrmecia was rediscovered on 22 October 1977 southeast of Ceduna on the Eyre Peninsula of South Australia by a CSIRO field party that had camped overnight en route from Canberra to Western Australia. Workers and dealate queens were collected while foraging nocturnally on the ground and tree trunks in disturbed roadside mallee woodland, but colonies were not located. The collection site is about 1000 kilometers east of the Balladonia-Thomas River Track, which the party later surveyed without finding the ant, despite knowledge of its likely habitat preferences. Another well-informed party has since worked the area south of Balladonia, without success. In a visit in mid-November to Eyre Peninsula Philip S. Ward and I began systematic field studies and secured several colonies, complete with queens, larvae, and pupae. These colonies have since yielded alate females and males.

Identification
Taylor's 1978 description of the general morphology (see below) is helpful for identification.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Taylor (1978) reported the following about the intial collections and colonies found when this ant was rediscovered in 1977 - Nothomyrmecia workers were readily collected on Eucalyptus trunks at night, but they could not be found during day-time. Night search in surrounding areas shows that the population is apparently very local, occupying only several hectares. The ant seems absent from apparently similar adjacent sites. Nest entrances, when located, consisted of small (about 4 to 6 mm), unspecific holes in the ground under shallow leaf litter, without surrounding mounds or deposited soil. Location of further populations will almost certainly require night search, since the presence of Nothomyrmecia is not evidenced during the day. The ants forage singly and range to the tops of the trees, where they probably seek sweet substances and hunt for small arthropods. The remains of a small unidentifiable microlepidopteran and a spiderling have been taken from foragers. Workers feed avidly from baits of honey streaked on the tree trunks and imbibing for long periods, often exceeding 30 minutes. Their gasters visibly expand with crop expansion, although the sclerites do not separate sufficiently to expose the intersegmental membranes. After feeding, foragers continue to stray on the trees, apparently randomly, and observers experience great difficulty in tracking the return of the ants to nests, at least until around dawn. At first light, the ants begin to leave the trees, proceeding directly and positively across the surrounding leaf litter to the nest entrances, which are located in open ground and are evidently not associated with basal accumulations of bark litter and debris near trees. Incomplete observations, interrupted by bad weather, suggest that there might be a considerable exodus from the nests at dusk, with few foragers returning until near dawn. If this is true, the position of the sun or light areas of the sky would be similarly related to the body axis on both journeys. There is no evidence that chemical trails are laid by foragers, and, unlike smaller Myrmecia species, they show no structured jumping or hopping behavior. Disturbed foragers sometimes adopt a stationary open-jawed threatening stance, but they usually fall abruptly to the ground and feign death in a cryptic, motionless pupal posture. A Myrmecia species, similar in size to Nothomyrmecia, is an equivalent diurnal forager, first appearing as Nothomyrmecia withdraws. A few dealate queens of Nothomyrmecia were encountered among the workers. When tracked to nests they proved to be colony founders, following the incompletely claustral mode of establishment, in which young queens leave their immature first brood in order to forage.

Five Nothomyrmecia nests were excavated on 17 to 18 November. In each a single gallery (diameter, 4 to 5 mm) descended steeply at about 60° to a terminal, subelliptical, horizontal chamber (diameter, 3 to 5 cm; height, 5 to 10 mm; depth below ground, ranging from 18 to 43 cm). Each shaft had three to five side chambers, one within 10 cm of the surface. The ants retreated timidly, most being captured with brood and queens (one in each nest) in the terminal galleries. The brood comprised numerous half-to full-sized larvae, all probably of a single generation, and a few pupae; eggs were not seen. Callow adults, alate queens, and males were absent. Mature nests probably contain 50 to 70 workers. A dense layer of calcrete rocks in the soil profile apparently limited nest depth. A sixth nest penetrated this, and excavation was abandoned.

By 9 March 1978, four colonies, two with queens, survived in laboratory culture. Additional larvae had not been produced, and all but a few in two nests had pupated. Workers began emerging from 24 December, males from 16 January, queens from 20 January. Callows are recognizable for about 2 days. Emergence seemed due for completion by mid-April. One colony produced males, and another males plus queens. The latter began emerging on 20 January and 3 March, respectively, possibly in a natural sequence. Both trophic and apparently reproductive eggs were laid occasionally, but consistently, by workers. These were fed mostly to larvae, but also to other adults, including mother queens and alate sexuals. Oviposition by queens was not observed. No reproductive eggs were accumulated. Two observation series of assembled foragers were collected on 23 October and 17 to 18 November. The first included a (presumably colony-founding) dealate female. Both of these groups accumulated many reproductive eggs from late December onward, and a few of these hatched by mid-February; pupation had not occurred by 9 March. It is not known whether the dealate female in the mixed group contributed eggs, but oviposition by workers was seen. Production of eggs is thus not inhibited by laboratory conditions. These events suggest that brood is normally not present in colonies during winter (say from late April to early September). As a result, foraging in this season is likely to be reduced, and nests possibly sealed, as in Myrmecia tarsata, which does not over-winter brood (personal observation).

A further nest, with a single terminal chamber 18 cm below ground, was also excavated. This contained two dealate queens. Brood was not seen and, if present, must have been small. This nest was located by tracking a foraging queen at dawn from a tree 4.5 meters away. One queen left the nest briefly at night in light rain to drink water from fallen leaves. These ants survived in culture without evident antagonism, and on 9 March were supporting a large larva and a co-coon, which was smaller than those in mature colonies and was spun on 28 February. Larvae were fed with insect fragments and apparently normal (reproductive as opposed to trophic) eggs by both queens. Founding thus may be pleometrotic with queens evidently reduced later to one (secondary monogyny). Mating flight details are unknown. The queens might flutter from vegetation, like some brachypterous Myrmecia (personal observation). None had undergone dealation as virgins in the nests by 9 March. Alates are presumably released by late summer or autumn (March or April) but might be overwintered in parent nests. Founding queens excavate to considerable depth; and, even if released in late summer, evidently mature no eggs until spring.

Aptery or brachyptery in Myrmecia queens is not uncommon; although its adaptiveness is unclear, it might sometimes involve premating isolating mechanisms. This seems unlikely in Nothomyrmecia, where brachyptery might relate to population structure, as an adaptation developed in small scattered populations held in enclaves by competition with other ants, or by precise, unusual, ecological requirements. It might be inadaptative for queens to disperse and attempt to establish colonies away from enclaves. The situation could be compared to that of brachypterous mountaintop or island insects, and Nothomyrmecia could be dangerously overspecialized in this regard. Brachyptery might be recently evolved; female wings, if nonfunctional for dispersal, would probably quickly dis-appear altogether. Short-winged queens might be irregular products of drought-stressed colonies, as has been reported in some Chelaner (Myrmicinae) species in semiarid Australia, but no available evidence suggests such dimorphism in Nothomyrmecia.

Adult N. macrops are largely nectarivorous but drink hemolymph from insect prey. The latter, with little dissection, is fed directly to larvae. Larvae can move independently toward food, and cannibalism among them seems rare. Pupae are used for larval food if forage is withheld. Eggs are scattered in observation nests, with larvae plus eggs and pupal cocoons only roughly segregated. Mature larvae swell anteriorly before spinning cocoons and are buried by workers to facilitate cocoon formation. Emergence from cocoons is often assisted by nurses, which tend to be the smaller, least aggressive workers. Occasional trophallaxis has been seen between workers, and with sexuals or larvae, which exude anal droplets imbibed by workers. Workers and females actively groom each other, with special attention to the posterior mesosoma (? metapleural glands). They will collapse tonically immobile in pupal posture if nests are jolted, or if dragged or carried by nest mates. Queens or workers may be dragged by antennae or limbs without tonic immobility, sometimes by counteracting workers, and appear from abdominal movements to stridulate if distressed by this. Stridulation occurs when workers, queens, or males are held; but it is neither easily induced nor is it continuous, especially in males. Digging is induced when nest soil is moistened. Refuse heaps, including food wastes, discarded cocoons, and dead immatures or adults, are accumulated away from the occupied sections of nests. Wastes are regularly deposited in the small (15 mm in diameter) dishes used for feeding honey, which are frequently filled with soil, even by colony-founding queens. These seem to be behaviorally totipotent compared with workers. Males are occasionally observed riding for many minutes on alate female nest mates, without attempting copulation. All standard self-grooming routines are actively practiced, except abdominal tip licking, which has not been seen. Alarm communication is slow and inefficient. The ants are generally nonaggressive, differing markedly from most Myrmecia. Territoriality between colonies is not evidenced in either field or laboratory. Allozyme markers suggest that several colonies can contribute foragers to single trees. Workers transferred to alien colonies are shown little aggression. Mixed foragers will settle to behave like queenless colony fragments and will adopt foraging queens.

Genetics
Preliminary investigations show that Nothomyrmecia has a very high diploid chromosome number of about 92, the highest number known among Hymenoptera, where the range other-wise is 2n = 6 to 84. This range is encompassed by the ants, and all Hymenoptera with 2n exceeding 52 are ants. Most are Myrmecia species, of which ten have been investigated yielding a 2n range of 9 to 84. Four species of Myrmecia, with 2n = 60, 66, 81, and 84, have diploid numbers exceeding 52, and a Bothroponera species (Ponerinae) has 2n = 60. Most Nothomyrmecia chromosomes are dotlike acrocentrics, but some larger metacentrics are present.

Morphology
Taylor (1978) - Workers of N. macrops average about 10 millimeters in length. Although often likened superficially to Myrmecia, they more closely recall the formicine weaver ants of genus Oecophylla. Their pale yellowish-brown color and large eyes have been correctly interpreted as indicating nocturnality. The elongate-triangular mandibles, with spaced minute teeth, are less specialized than those of Myrmecia, and Prionomyrmex is intermediate. Ocelli are present but vestigial. The exoskeleton, especially that of the gaster, is less heavily sclerotized than in Myrmecia, is moderately heavily sculptured, and bears abundant long erect hairs. The first metasomal segment (abdominal II) forms a petiole, and, unlike Myrmecia, Prionomyrmex, or Ameghinoa, there is no constriction behind abdominal III, delimiting a postpetiole. The sting is prominent and effective, with moderately painful delivery. The meta-pleural glands each comprise a dense pad of very small cells, whereas most other ants investigated have many fewer, loosely scattered, large cells, as in Myrmica (Myrmicinae). A large thin-walled apical extension of each metapleural bulla receives the numerous glandular ducts and apparently represents an expanded "sieve plate." Myrmecia has a similar metapleural gland structure, which might be unusual among ants.

Perhaps the most astonishing discovery of my investigation is the stridulatory organ of Nothomyrmecia. This organ consists of the usual plectrum and stridulitrum arrangement between abdominal segments III and IV. However, the organ is here uniquely positioned ventrally, involving the sterites. Stridulatory organs found among other ants are dorsal and tergal, and neither type is present in Myrmecia. Other hymenopterous abdominal stridulatory organs are always dorsal, with stridulitrum on either the IV or V tergite, and plectrum on the one preceding.

Females differ from workers in the expected features. They are slightly larger on average, with similar general structure, including that of abdominal segments III and IV, which also bear a ventral stridulatory organ. Ocelli are well developed, but the eyes are not significantly enlarged. The pterothoracic sclerites are structured as usual in flying ants, although they occupy less of the mesosomal bulk than is usual. This peculiarity relates to the un-expected and specialized brachyptery of the alate queens, the wings of which barely overlap the first gastral segment (abdominal III). They are not only scaled down relative to those of males, but they are also peculiarly trimmed, although a frenal fold and hamuli are retained. The reduced mesosomal structure resembles that of some brachypterous Myrmecia species.

Males superficially resemble those of Myrmecia but have a single waist node. The wings are long, with a full, primitive, venational complement. The median vein leaves the cubital proximal to the root of the cubito-anal cross vein, an unusual feature convergently developed in Dorylinae, Ecitoninae, and Typhlomyrmex (Ponerinae). An anal (that is, jugal) lobe is present on the hind wing, as is the case in various primitive ants; but a series of basal hamuli in addition to the apical set occurs only in Nothomyrmecia among formicids and is a primitive character. The forelegs of most, but not every, male specimen each bear two apical tibial spurs, one a long calcar, the other a short thick cone. All other Hymenoptera, except some primitive Symphyta and Proctotrupoidea and all Ceraphronoidea, have single foretibial spurs. Some illustrations of Sphecomyrma freyi incorrectly depict paired spurs in that species. The mesoscutum carries parapsidal furrows, but notauli are lacking, a clearly derived condition. A functional ventral stridulatory organ, like that of the female castes, is present. Significance of genitalic structures cannot be estimated in the absence of comparative studies. Cerci are present; sternite IX has a bifid apex; the gonoforceps are divided into proximal and distal sections and lack the dorsal projection present in some Myrmecia species; the volsellae are unspecialized, and the penis valves are strikingly elaborate, with several denticulate apical processes.

Adult Nothomyrmecia and Myrmecia share other significant primitive features including a formula of six maxillary and four labial palpae in all sexes; 12 antennal segments in female castes and 13 in males; paired calcariae on the middle and hind tibiae; tarsal claws each having a strong median tooth; and a sting whose complete structure includes a furcula and two-jointed gonostyli, as in other primitive ants. The proventriculus of workers is actively dammed, with the cuticular structure relatively unspecialized, that of Nothomyrmecia being similar to Pseudomyrmex (Pseudomyrmecinae). Most of these features are present in various other primitive ants of subfamilies Ponerinae and Pseudomyrmecinae.

Nothomyrmecia eggs, like those of Myrmecia are subspherical and non-adhesive. The larvae lack specialized tubercles and have a primitive shape and general structure, sharing many features with Myrmecia and with primitive prodoryline and proponerine Ponerinae, although the sensilla on the mouth-parts are more abundant. The pupal cocoons are substantial, but have thinner walls than those of Myrmecia and most primitive ponerines; meconia are produced.

In short, the general structure of adults and developmental stages confirms the primitiveness of Nothomyrmecia. Clearly derived features include the vestigial worker ocelli, female brachyptery, and male mesoscutal structure, whereas the abdominal and female mandibular structure, with the basal hamuli and two-segmented gonoforceps of the males, are features more primitive than those of Myrmecia. The stridulatory organ and supplementary male fore-tarsal spurs probably represent evolutionary novelties. The differences in waist structure separating Nothomyrmecia and the advanced myrmeciines are neither superficial nor trivial. Abdominal segment IV of Myrmecia is "tubulate" in form, with its acrotergum and acrosternum each broadly expanded and separated from the body of its plate by a transverse construction and incised groove, presumably representing the antecostal suture. In addition, the lateral edges of these plates are aligned and intimately associated, especially in the anterior portion, which at rest is fully inserted into segment III (the postpetiole), the posterior edge of which embraces the antecostal constriction of segment IV to form a ball joint. Controlled telescopic and rotational movement at this node facilitates abdominal mobility. Similar tubulation of segment III was doubtless important in evolution of the petiole-postpetiole joint in ants and other Hymenoptera. Evolution of the mesosomal-metasomal waist in primitive Aprocrita apparently involved acrotergal expansion. Subfamily Pseudomyrmecinae has been related to the Myrmeciinae and has a Myrmecia-like metasoma. Tubulation of abdominal IV is found in workers, queens, and most males of sub-family Ponerinae, where full lateral fusion of the sclerites is frequent and the structure is sometimes further elaborated. Tubulation evidently functions as a preadaptation to postpetiole formation, which has been important in evolution within and beyond the Ponerinae. In contrast, Nothomyrmecia has the sclerites of segment IV freely articulated, with structure similar to that of succeeding segments. The acrotergite and acrosternite are probably represented only by the thickened anterior rims of the sclerites, and the portion of each plate which inserts into segment III is only feebly differentiated, by superficial sculpture (which includes the sternal stridulitrum) from the exposed part. The structure is here nontubulate, and a postpetiole is not differentiated. A generally Nothomyrmecia-like segment IV is considered primitive to that of Myrmecia, because this is the condition in most aculeates, and probably in Sphecomyrma.

Nomenclature

 *  macrops. Nothomyrmecia macrops Clark, 1934a: 19, fig. 1 (w.) AUSTRALIA. Taylor, 1978a: 979 (q.m.); Wheeler, G.C., Wheeler, J. & Taylor, 1980: 131 (l.); Imai, Taylor, et al. 1991: 133 (k.). Combination in †Prionomyrmex: Baroni Urbani, 2000: 479; in Nothomyrmecia: Ward & Brady, 2003: 375. See also: Jaisson, Fresnau, et al. 1992: 425; Hölldobler & Taylor, 1983: 382; Ward & Taylor, 1981: 177.

Worker
Length, 9.7-11 mm.

Testaceous, basal half of first segment of gaster darker. Mandibles, clypeus, antennae and legs pale yellow.

Mandibles very finely and densely punctate, with a row of large punctures along inner border at base of teeth. Clypeus and head very finely and superficially reticulate. Pronotum finely rugose, the rugae forming feeble transversely arched ridges. Mesonotum finely reticulate with a few large shallow punctures. Epinotum transversely and finely rugose. Node smooth in front, finely reticulate and with a few large punctures behind. Postpetiole gaster, antennae and legs microscopically punctate.

Hair yellow, erect, moderately long and abundant throughout, shorter and suberect on antennae and legs. Pubescence white, very fine and adpressed, abundant throughout but not hiding the sculpture.

Head as long as broad, much broader behind than in front, broadest just behind the eyes, sides convex, occipital border strongly concave, angles strongly rounded. Mandibles shorter than head, external borders straight to apical third then rounded inward and downward; inner border straight to basal fourth then abruptly reduced to base, furnished with ten or twelve small sharp teeth, about equally spaced along the edge, with minute denticles between them, basal angle sharp, apex long and pointed. Clypeus feebly convex above, produced and convex in front. Frontal carinae erect, almost parallel, extending backward level with middle of eyes, not covering the antennal insertions in front. Eyes large and convex, placed at middle of sides slightly on top, occupying fully one-third of sides. No ocelli. Scapes extending beyond occipital border by one-fifth their length, slightly thickened toward the apex; second segment of funiculus one-fourth longer than first, third and fourth, these equal in length, fifth to tenth becoming gradually shorter, apical as long as the two preceding together. Thorax two and three-quarters times longer than broad. Pronotum slightly broader than long, strongly convex in all directions. Mesonotum almost as long as broad, almost circular, strongly convex transversely. Epinotum longer than broad, convex in all directions; in profile the dorsum and declivity strongly convex without traces of a boundary. Node slightly broader than long, bluntly pointed in front, convex in all directions; in profile longer than high, dome shaped but slightly higher in front than behind, one-third longer than the stalk in front; ventral surface with a long broad bluntly pointed tooth in front directed downward. No traces of a constriction between the postpetiole and gaster. Postpetiole twice as broad as long, bell-shaped; ventral surface with a long sharp, hook-shaped, semitransparent tooth directed backward. First segment of gaster one-third broader than long, broader behind than in front, sides strongly convex. Sting very long and stout. Legs robust.

Type Material


Western Australia, Russell Range (Miss A. E. Baesjou). Described from two examples captured by Miss Baesjou near the Russell Range, inland from Israelite Bay.

Taylor (1978) had this to say about the vaguely noted type locality: Clark's specimens were probably collected near the western end of the Great Australian Bight by an excursion party that traveled, in December 1931, southward from near Balladonia through mallee-type Eucalyptus woodland and forest and set up camp for several weeks at the Thomas River mouth, east of Esperance, in the extensive sand plain heath present there. Insects were collected, without precise data, for a local naturalist, Mrs. A. E. Crocker, who sent them to Clark. Many Australian and American collectors and expeditions have since unsuccessfully sought Nothomyrmecia in this area, especially in the sand plain heath, where a guild of similarly pale colored, large-eyed, nocturnally foraging ants is well represented.