Temnothorax obturator

Mackay (2000) "Colonies are found in live oak galls (Quercus virginiana Mill.) or hollow twigs of the wafer ash and ironwood (Wheeler, 1903a; Moody and Francke, 1982; Longino and Wheeler, 1987; Wheeler and Longino,1988). Nests are monogynous (Frumhof and Ward, 1992). The female enters the gall, plugs the entrance and begins egg laying. Later the workers open gall, but the entrance hole is so small, the queen remains trapped in the gall. Sexuals appear in nests in late May, but it is not clear how the virgin females exit through the tiny exit hole. Nests contain up to 36 or 40 workers. They are extremely hostile to workers from other nests."

Identification
Mackay (2000) "The peculiar propodeal spines united by a carina easily distinguish this species from all other known North American Temnothorax. The petiolar node is also rounded and poorly defined, which will also help separate it from other species in the genus. The propodeum is lower than the mesonotum and appears depressed. The antenna has 12 segments."

Distribution
United States. Central Texas.

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Habitat
Woodlands

Abundance
Locally common

Biology
Wheeler (1903): Described from many specimens collected at different times from the abandoned Holcaspis cinerosus galls on the live-oaks (Q. virginiana). The young fertilized queen, on entering the gall to establish her colony, gnaws minute fragments from the ligneous wall, mixes these with some secretion,(saliva?) and completely plugs up the round opening through which the Holcaspis escaped and she herself has entered. Later when the first batch of tiny workers appear, they perforate the center of the plug with a small opening like a pin-prick, and just large enough for egress and ingress. This opening is too small for the queen to pass, so that she remains imprisoned. With the growth of the colony the chamber formerly made and inhabited by the Holcaspis larva is enlarged by the workers. The queen with the larval prefers to inhabit the small central capsule in which the Holcaspispassed its pupal life. The larval are of a peculiar greenish tint. The males and virgin females make their appearance in the colony during the last week of May. At no time are the colonies of Temnothorax obturator very large. They rarely comprise more than 36 or 40 workers. Members of different colonies, even from galls on the same branch, are extremely hostile to one another. Along the creek-bottoms near Austin, Temnothorax obturator is also occasionally found nesting in the-twigs of the wafer ash (Ptelea trifoliata) which have been hollowed out by tiny carpenter-bees (Ceratina nanula Ckll. and C. arizonensis Ckll.). The relatively large entrance made by the bees at the end of the twig is plugged up by the ants with agglutinated vegetable particles and then perforated with a minute opening in the center.

and some additional notes, modified from Longino and Wheeler (1987)

"Temnothorax obturator was the most common ant found nesting in galls in surveys conducted in three sites, in three different counties, in Texas. Galls inhabited by this species showed the typical plug built by the queen and the pin-prick-sized hole opened by the workers. Entire colonies could be found within a gall, with the workers carrying out considerable excavation. In Bexar County, queens, eggs, larvae and pupae were collected from March to October. On June 16 one gall contained 4 winged females and one male; another contained a single winged female. On the same date an incipient colony in a plugged gall contained a queen and young brood. This shows it is possible for colonies to spend their entire life cycle in a gall.

Temnothorax obturator was found nesting away from oak galls at the Webberville site. No oak galls were found, but three colonies of Temnothorax obturator were found in the dead twigs of Bumelia lanuginosa (ironwood).

Temnothorax obturator appears to be a specialized inhabitant of Disholcaspis cinerosa galls on live oaks but can nest elsewhere."

Nesting Biology
Arboreal nester. Prefers galls that have been damaged by other organisms. A queen enters the gall through a premade hole, seals herself in through making a plug of plant material and after her workers emerge they create a pin sized hole in order to forage outside the nest. Temnothorax obturator will also nest in dead branches of a few different plant species. A similar pattern of nesting to what occurs in galls is followed, with queens finding premade holes created by other organisms.

Reproduction
Winged reproductives were found in nests in the June.

Plants
This ant has been found nesting in
 * galls of live-oaks (Quercus virginiana)
 * hollow branches of living ironwood (Bumelia lanuginosa) and wafer ash (Ptelea trifoliata) plants

Nomenclature

 *  obturator. Leptothorax obturator Wheeler, W.M. 1903c: 249, pl. 12, fig. 19 (w.q.m.) U.S.A. Wheeler, W.M. 1903f: 662 (gynandromorph); Wheeler, G.C. & Wheeler, J. 1955b: 24 (l.). Combination in L. (Myrafant): Smith, D.R. 1979: 1394; in Temnothorax: Bolton, 2003: 271. See also: Mackay, 2000: 382.

Worker
Length 2.25-2.75 mm. Mandibles 5-toothed. Clypeus rather fiat, its anterior margin broadly truncated in the middle. Antennae 12-jointed; scape reaching posterior angle of head; first funicular joint as long as the three succeeding joints; joints 3-8 broader than long, joints 9-11 forming a club, the ninth distinctly narrower and shorter than the tenth, the terminal joint longer and considerably thicker than the two preceding joints. Thorax slender, somewhat broader in front than behind; rounded at the hi.uneri, in profile convex in front and slightly concave behind on the dorsal surface, without mesoepinotal constriction. Epinotal spines small, rather acute, not longer than broad at their bases, nor further apart than long, directed upward. In front and on the side of each epinotal spine there is a distinct longitudinal swelling or ridge on the epinotum. Petiole very slender, three times as long as broad, sides of the node parallel, the peduncle somewhat narrower when seen from above; in profile the lower surface is evenly concave, the anterior tooth minute; the dorsal surface with a low regularly rounded, knoll-like node. Postpetiole small, about 1 1/2 times as broad as the petiole, as broad as long, square when seen from above, with prominent anterior angles ;in profile the lower surface is flattened, the upper convex, especially in front. Gaster with distinct anterior angles. Sting well developed.

Mandibles opaque, striated and with a few coarse punctures. Clypeus subopaque, its whole surface longitudinally rugose. Head subopaque in front and on the sides, shining behind, on the former regions densely and rather finely reticulate-rugose; the rugal with a distinct longitudinal trend except on an opaque patch above each eye, where the rugae are evenly reticulate. The shining portion of the head is traversed by clean-cut longitudinal rugae much farther apart than on the front and crown and interspersed with a few coarse punctures; posterior angles of head delicately reticulate. Thorax subopaque; pronotal region more shining, foveolate-reticulate on the whole dorsal surface; pleural more coarsely reticulate-rugose, with pronounced longitudinal trend in a few of the rugal, especially in the upper meso and lower metapleurae. Petiole and postpetiole subopaque, rather evenly foveolate-reticulate. Gaster smooth and shining.

Hairs moderately abundant, snow-white; clavate on the crown of the head, thorax, pedicel and gaster; a little longer on the pedicel and gaster and somewhat more reclinate. Hairs on the legs and antennae sparse, non-clavate, appressed and inconspicuous.

Black or very dark-brown. Mandibles, joints 3-9 of the antennae, neck, ventral surface of petiole and postpetiole reddish-yellow. Legs reddish-yellow, except the middle of the coxae, femora, tibial and last tarsal joint; which are black.

Queen
Length 3.5-3.75 mm. Clypeus and head more coarsely longitudinally rugose and more opaque than in the worker. Thorax subopaque; neck delicately reticulate-rugose; pronotum transversely and irregularly rugose; mesonotum, paraptera and scutellum traversed by dense, parallel, clean-cut, longitudinal rugal. Epinotum delicately and somewhat concentrically reticulate-rugose; armed with two inconspicuous swellings in the place of the spines; pleural longitudinally rugose. Petiole and postpetiole like those of the worker, the node of the former relatively lower; postpetiole hardly 1 1/2 times as broad as the petiole. The white hairs on the body are non-clavate, though those on the pedicel and gaster are somewhat thickened. Head, thorax and pedicel yellowish-red or dark-red, their upper surfaces more or less infuscated. Gaster black. Antennal scape black with basal half yellow; first joint of funiculus and club black, remaining joints yellow. Legs colored like those of the worker. Wings milky-white, veins yellow; stigma brown, conspicuous.

Male
Length 1.5-2 mm. Head as long as broad, exclusive of the mandibles; cheeks very short. Mandibles meeting with their tips. Clypeus convex, truncated in front. Antennae slender; 13-jointed; scape nearly as long as the first five joints of the flagellum; first flagellar joint thickened, nearly as long as the three following joints together; joints 2-8 of the flagellum cylindrical, as long as broad; the four terminal joints forming a club, of which the three basal joints are subequal in length but increase somewhat in thickness distally; terminal joint much larger, distinctly longer than the two preceding joints. Epinotum with two very inconspicuous thickenings in the place of the spines. Petiole and postpetiole similar in shape to the corresponding segments of the worker, node of former very low.

Clypeus shining, with a few reticulate ruga: forming rather large meshes. Head, thorax and pedicel opaque, finely and evenly reticulate-rugose. Mesonotum sparsely foveolate-punctate and traversed by a narrow, smooth, longitudinal stripe. Pleura: shining in part. Gaster smooth and shining.

Hairs white, sparse, non-clavate, most abundant on the thoracic dorsum, pedicel and gaster.

Black; pleura: and pedicel more piceous. Mandibles, legs and antenna: white; the mandibles with brown edges, the antennae with scape, second joint and club blackened; legs with the coxae, middle of the femora and tibia: and the last tarsal joint blackened.

Type Material
As reported in Mackay (2000) "AMNH, MCZC [seen]"

Type Locality Information
USA. Austin, TX.

Additional References

 * Longino, J. T. and J. Wheeler. 1987. Ants in live oak galls in Texas. National Geographic Research. 3:125-127.
 * MacKay, W. P. 2000. A review of the New World ants of the subgenus Myrafant, (Genus Leptothorax) (Hymenoptera: Formicidae). Sociobiology. 36:265-444.
 * Wheeler, W. M. 1903. A revision of the North American ants of the genus Leptothorax Mayr. Proceedings of the Academy of Natural Sciences of Philadelphia. 55:215-260.