Temnothorax ambiguus

Temnothorax ambiguus has small colonies (< 100 workers), nests in the soil or in small hollow cavities that are contiguous with or just above the soil surface (dead roots, dead stems, at the base of vegetation, in leaf litter, etc.) and forages for honeydew and dead insects.

Identification
Wesson and Wesson (1940) noted that Emery's description was not sufficient to separate this species from Temnothorax curvispinosus, which Temnothorax ambiguus closely resembles, and offered the following: "Differs from the worker of Temnothorax curvispinosus in the following characters: 1) The epinotal spines are shorter, from 1/2 to 2/3 the length in Temnothorax curvispinosus, as far apart at the base as they are long, slightly diverging, obtusely pointed. 2) The petiole is proportionately shorter and the node higher than, in Temnothorax curvispinosus, only slightly compressed laterally above when seen from behind, the anterior slope concave and steep, the posterior slope sharply convex or angulate. 3) The postpetiole in profile is larger in proportion to the petiole, and is subquadrate; from above, the postpetiole is rectangular, 1-1/4 times as broad as long. 4) The sculpture on the thorax is more opaque than in Temnothorax curvispinosus and more uniform; the rugae are more irregular and the interrugal spaces coarsely and densely recticulate-punctate. 5) The color is uniformly tawny yellow, the spots on the sides of the gaster in Temnothorax curvispinosus being absent in ambiguus."

Distribution
Creighton (1950): "eastern Canada and New England west to the Dakotas. In the east the southern limit of the range seems to lie at the latitude of Pennsylvania and Ohio."

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

Habitat
Occurs in woodlands and moist habitats (e.g., fens, bogs) in some areas of its range (e.g., northeastern NA) but is a dry-mesic and mesic grassland species in the Midwest where it can be found in prairies and old fields.

Abundance
Common

Missouri
(Antweb) Temnothorax ambiguus is very commonly associated, in prairie and prairie-like habitats, with Formica incerta, Aphaenogaster N16, Myrmica af-evani, Myrmica af-sculpt and Tapinoma sessile. T. ambiguus is frequently seen as individual foraging workers on the ground and on vegetation. It laps up honeydew ejected onto foliage and litter on the ground, and may also be seen transporting small insects. Alates are attracted to lights on warm, humid nights in early summer.

It nests in rhizomatous bases, dead leaf sheaths and soil in the tufts and root-zone of native plants, especially clumping grasses. It also nests in the interstices of mound nests of prairie Formica species.



North Dakota
Wheeler and Wheeler (1963): "This tiny timid yellowish ant has been found only a few times in North Dakota in woodlands and only once in grasslands. It seems to be much more common further east, where it occurs in woods or, more often, in grassy areas.

Ohio
Wesson and Wesson (1940)


 * "This species seems to be typically a meadow ant. We have found it in nearly every growth of beard grass that we have examined, less often in more thickly vegetated fields. Several colonies were found in a moist sunny pasture in the bottom of a gulch. The colonies usually nest in hollow dead stems at the base of grass tufts, although one colony from the low pasture was nesting in the soil.


 * described the subspecies Leptothorax ambiguus pinetorum from south central Ohio (Jackson Co.). "Described from a colony comprising 12 workers, 1 dealate female, 2 alate females and 5 males, taken July 10, 1938, Jackson County. The colony was nesting in a small, hollow, dead root covered by pine needles on the edge of a dry piney bluff. Four colonies and several stray workers of this form have been taken in or near the type locality. All have been small, comprising 10 to 25 workers. Besides the type colony, one nest consisted of a small hollow twig, another of a curled-up dead leaf, both just under the pine needles. The fourth colony was nesting in the bark of a pine log."

Foraging/Diet
General scavengers, mainly collecting insect parts and lapping up of liquids.

Colony Attributes
Colonies typically contain less than one hundred workers although an occasional nest can be found that exceeds this number. Roughly half of the queens survive the winter, for workers roughly two thirds to slightly more than one half survive from fall to spring.

(Herbers, her co-workers and others).

Nesting Biology
Temnothorax ambiguus will nest in soil, dead stems, grass clumps, hollow twigs, acorns and other preformed cavities.

In the northeastern hardwoods, at least, there is quite a bit known about nest use. Nests are located in preformed cavities in structures found in the litter, e.g., in small sticks or nuts. This ant is facultatively polydomous and their nesting arrangements vary with season. In the productive summer months, colonies can fragment and be arranged across numerous nest sites. These vary in queen number, from multiple queens to those that only have workers and brood.

During the winter nests coalesce and typically are found in a single structure. Nest mortality can be significant. From one third to one half of all nests are gone by the end of the winter. Some of these losses are colony deaths while others represent migration to a new nest site, which likely occurs during warmer winter days.

(based, in part, on Herbers and Johnson 2007, Alloway 1983)

Reproduction
Queen number can vary by colony and season. New colonies are founded by pleoemetrosis and new queens are likely adopted into existing nests. The latter is evident from the presence within populations of both monogynous and polygonous nests. Reproductive queens contain 6 ovarioles. Worker reproduction does occur with some male production possible from worker derived eggs. Reproductive workers contain 2 ovarioles.

Reproductive flights take place in early summer in the middle latitudes of this species' range. Males were found in nests in early July in Ohio (Wesson and Wesson 1940) and in Missouri "alates are attracted to lights on warm, humid nights in early summer."). This timing may vary further north and south.

New queens are produced in some queenless nests. These are presumed to be nests that are separated from a queenright nests or from a nest that had earlier lost its queen(s).

(based, in part, on Herbers and Johnson 2007, Alloway 1983)

Kannowski (1959) noted the following concerning Temnothorax ambiguus reproduction in southeastern Michigan: "Alates were found in nests between July 9 and August 29, but were seldom numerous. This condition plus the fact that the pupae of the alate forms were found for 3 to 4 weeks after the first alates have appeared suggests that alates fly very soon after maturing, probably remaining in the nest only for a few days to complete the maturation process. Flights probably occur in late July and August, but none were seen. What may have been a prelude to a flight was observed about noon on July 26, 1954 at Mud Lake Bog. Alates of both sexes were crawling on sedge stems and on moss near a nest, but did not fly. Many workers were active among the alates; they did not, however, deter the alates from their activities. At the time of this activity the nest was largely shaded and the temperature was 85 ~ F."

Behavior
Stuart (1981) studied inter- and intra-specific interactions between co-occuring Temnothorax colonies and found: "Queenless, monogynous and polygynous nests showed no significant differences in aggressiveness. However, larger nests were significantly more aggressive than smaller nests and heterospecifics were attacked more frequently and more intensively than conspecifics."

Herbers (1983) studied time budgets and social organization: Workers exhibit a total of 46 behaviors, queens 13. Queens were less active and much of their activity focused on the brood. Workers spent the most time: (averages) 68% motionless, 13.8% walking within the nest and 5% self-grooming. The sum of their social behaviors were less than 15% of the workers' time. Worker social actions were grouped within four roles (brood care, social interactions, physical nest maintenance and provisioning) and workers did tend to specialize on activities within a single role in the short term. This tendency was weaker over 30 minute periods, as compared to observing transitions from one action to the next.

Other Ants
This species is parasitized by three species of slave-making ants: Temnothorax duloticus, an undescribed Temnothorax species and Temnothorax americanus. (Talbot 1957, Beibl et al. 2005).

Morphology
Worker head width is normally distributed: average head width = 0.552 mm, s 0.043 mm (n = 50).

Nomenclature

 *  ambiguus. Leptothorax (Leptothorax) curvispinosus subsp. ambiguus Emery, 1895c: 320 (w.) U.S.A. Wesson, L.G. & Wesson, R.G. 1940: 97 (q.m.); Wheeler, G.C. & Wheeler, J. 1955b: 22 (l.). Combination in L. (Myrafant): Smith, D.R. 1979: 1392; in Temnothorax: Bolton, 2003: 271. Raised to species: Wesson, L.G. & Wesson, R.G. 1940: 97. See also: Mackay, 2000: 312. Current subspecies: nominal plus foveatus, pinetorum.

Worker
unterscheidet sich vom typischen curvispinosus durch die etwas grobere, abel' zugleich weniger dichte Sculptur sowie durch die Metanotumdornen, welche kiirzer und fast gerade sind. Hill City, S. Dakota (PERGANDE); Cleveland, Ohio (von Herrn WASMANN eingesandt); N. York (SCHMELTER).

Wesson and Wesson (1940) Differs from the worker of Temnothorax curvispinosus in the following characters: 1) The epinotal spines are shorter, from 1/2 to 2/3 the length in Temnothorax curvispinosus, as far apart at the base as they are long, slightly diverging, obtusely pointed. 2) The petiole is proportionately shorter and the node higher than, in Temnothorax curvispinosus, only slightly compressed laterally above when seen from behind, the anterior slope concave and steep, the posterior slope sharply convex or angulate. 3) The postpetiole in profile is larger in proportion to the petiole, and is subquadrate; from above, the postpetiole is rectangular, 1-1/4 times as broad as long. 4) The sculpture on the thorax is more opaque than in Temnothorax curvispinosus and more uniform; the rugae are more irregular and the interrugal spaces coarsely and densely recticulate-punctate. 5) The color is uniformly tawny yellow, the spots on the sides of the gaster in Temnothorax curvispinosus being absent in ambiguus.

Queen
Wesson and Wesson (1940) Differs from the female of Temnothorax curvispinosus as follows: 1) The epinotal spines are obtuse, as broad as long at the base. 2) Petiole and post- petiole as in the worker, and differing from the curvispinosus female in the same manner as do the workers of the two forms. 4) The sculpture is less shining.

Male
Wesson and Wesson (1940) Differs as follows from the male of Temnothorax curvispinosus. 1) Smaller size (2.2-2.4 mm). 2) The epinotum lacks spines, bearing instead small, low, broadly rounded tuberosities. 3) Front and vertex are rather delicately reticulate-rugose, without the more prominent longitudinal rugae of v curvispinosus. 4) Color is lighter than in Temnothorax curvispinosus, very pale yellow, gaster and head slightly darker.

Type Material
Hill City, South Dakota by present restriction, , as reported by Creighton (1950)