Strumigenys nidifex

A Fiji endemic. This species is the largest Strumigenys known from Fiji and is the best known biologically. It has been found nesting in logs and under rocks. It prefers forest habitats but has also been found in disturbed areas. Foragers have been collected on numerous occasions.

Identification
Bolton (2000) - A member of the Strumigenys szalayi-group. A very distinctive large species, apparently restricted to the Fiji Islands. It is the only member of the group to have two intercalary denticles and retain spongiform tissue on the petiole.

Sarnat and Economo (2012) - Strumigenys nidifex is one of the most conspicuous dacetines of the Fijian fauna. It is the largest of the species, with a distinctive broad head that is impressed posterior to the vertex and bears a preocular impression on the ventrolateral margin of the head. All surfaces of the head, mesosoma, waist and coxae are punctate-reticulate. The nearest relative to S. nidifex is Strumigenys sp. FJ01. The gaster of the former is sculptured basally, but is otherwise strongly polished and shiny. The gaster of the latter is strongly punctate-striate the entire length of the first segment. The males of the two differ, with those of S. nidifex being larger with a distinctly elongated head, while the male of Strumigenys sp. FJ01 is smaller with a much rounder head. The queen of Strumigenys sp. FJ01 is also distinctly smaller, especially with regard to the mesonotum. However, the series of S. nidifex from Koro are all smaller, and the queens of that series are more similar to those of Strumigenys sp. FJ01 than to those of its conspecifics on other islands, with the caveat that its gaster is polished and shiny. Both species occur sympatrically in the Nadarivatu area. The only other species in Fiji with a preocular notch is Strumigenys rogeri, which is easily separated by its significantly smaller size, yellow brown color, and mandible with two pre-apical teeth. The other large Strumigenys in Fiji all lack the preocular impression.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Fiji.

Biology
Brown (1971) - Mann and Wilson both found S. nidifex a rather common ant in parts of Viti Levu, where it forms nests of up to 100 or more workers either in rotten wood on the densely shaded forest floor, between layers of stone, or in the earth under stones. Wilson found larvae in nests feeding on a worker-sized entomobryoid collembolan and on the femur of an orthopterous insect.

This indication of wide prey preference was fully borne out by observations made over 2 years on a laboratory nest of S. nidifex  (70 -80 workers and several dealates) that was sent by Wilson to the United States from Nadala, Fiji. This colony, kept in a small glass-topped plaster nest at home room temperature (68°-85° F), did exceedingly well in these artificial circumstances, and produced broods of males and queens 3 times in 2 years. The ants killed and fed to the larvae a wide variety of small arthropods, including mosquitoes, Drosophila, mites, aphids, beetles, blattarian nymphs, geophilomorph centipedes, and several different families of Collembola; in fact, they took almost all types of small arthropods offered to them. Poduroid collembolans were, however, definitely avoided and on several occasions when I maneuvered living poduroids so as to cause the ants to strike at them defensively, the ants immediately recoiled and began vigorous grooming of mandibles and anterior head, as though attempting to remove some noxious substance derived from the collembolans.

In hunting, the Strumigenys attacked quickly and directly, striking with the mandibles open to more than 180°, and stinging if the prey continued to struggle after being caught. Defensive behavior, observed when workers of the dacetine ants Strumigenys loriae, Strumigenys yaleogyna, and Strumigenys nigrescens were introduced into the S. nidifex foraging chamber, consists of repeated strikes with the mandibles followed by hurried retreats from the enemy.

Oviposition by queens was observed twice, and each time was accomplished in the same way. The gaster is brought forward under the head, and the head is held with the mandibles perpendicular to the floor; the stance is on all 6 legs. The egg slowly appears at the tip of the gaster, but it is not glossated or touched by the under-mouthparts; only occasionally is it touched gently by the antennae. After 8 or 10 minutes, the egg is received directly into the mandibles near their apices without touching the floor; the queen then carries it herself to the egg pile and places it there, after which she leaves it and shows no further interest in it.

Nomenclature

 *  nidifex. Strumigenys nidifex Mann, 1921: 464, fig. 23 (w.q.m.) FIJI IS. Wheeler, G.C. & Wheeler, J. 1955a: 140 (l.). See also: Brown, 1971c: 81; Bolton, 2000: 905.

Worker
Bolton (2000) - TL 4.7-5.1, HL 1.38-1.48, HW 0.98-1.13, CI 71-76, ML 0.62-0.64, MI 43-46, SL 0.88-0.94, SI 83-90, PW 0.46-0.51, AL 1.34-1.44 (10 measured).

Apex of mandible with 2 intercalary denticles. Postbuccal groove inconspicuous. With head in profile dorsum very broadly and deeply concave from just behind level of eye to close to occipital margin; this concavity extending as a broad groove across entire width of vertex. Ventral surface of head with a distinct postocular concavity. Ventral surface of petiole with a narrow spongiform curtain, at least on posterior two-thirds of length. Entire alitrunk reticulate-punctate. Pronotal dorsum with a pair of erect hairs, as well as those at the humeri. Colour uniform dark brown to blackish-brown.

Queen
Brown (1971) - Showing the usual differences from worker; sculpture coarser, rugulose on alitruncal dorsum; postpetiolar disc striate; basigastric costulation denser and much longer than in worker.

Male
Brown (1971) - (1 specimen from a nest taken at Nadala, Fiji): TL 3.9, HL 0.83, HW (without compound eyes) 0.52, greatest diameter of compound eye 0.29, forewing L ca 3.4. WL (without cervix) 1.27 mm; CI 63.

Head slender, strongly depressed across occiput and deeply excised medially behind, forming narrow occipital lobes. Cervix prominent, depressed. Scutellum and metanotum protruding, both rounded; propodeal teeth low, rectangular. Nodes slender, without appendages, finely sculptured and opaque. Gaster smooth and shining, with a finely shagreened area at extreme base. Color dark brown, appendages lighter and more yellowish.

Type Material
Bolton (2000) - Syntype workers, queens and males, FIJI IS: Viti Levu, Nadarivatu (W. M. Mann) [examined].