Temnothorax rugatulus

Modified from Mackay (2000) Higher elevation coniferous forest species which occurs in moist habitats, in shaded grassy slopes with pines or grasslands. Temnothorax rugatulus can also be found in pinyon-juniper and cool desert habitats. Nests have been found in the soil, under rocks, in decaying wood, in grasses and in trees. Colonies may be monogynous, typically with a single macrogyne queen, or polygynous, with multiple microgyne queens.

Identification
Mackay (2000) "Workers of this species have an 11 segmented antenna, a coarsely rugose dorsal surface of the head, the dorsum (and sides to a lesser extent) of the mesosoma and petiole are rugose as the head, the propodeal spines are well developed, longer than the distance between their bases, the dorsum of the postpetiole has rough punctures.

This species can be recognized by the coarse rugae on the head, the areas between the rugae are punctured, but shiny (Fig. 156). This characteristic separates Temnothorax rugatulus from Temnothorax bradleyi and Temnothorax smithi. It is smaller than Temnothorax josephi and is basically concolorous medium yellowish-brown, often with dark infuscation on the head and mesosoma. The node of the petiole is rounded in profile, not truncate as in Temnothorax ambiguus. The subpetiolar process is often about as wide at the tip as it is at the base, although specimens that were previously referred to as Temnothorax rugatulus tend to have a tapered subpetiolar process. The propodeal spines are well developed, which separates it from Temnothorax schaumii, and Temnothorax whitfordi."

Range
CANADA, USA, MEXICO. Canada - British Colombia, Alberta. US - Washington, Oregon, Idaho, Montana, North Dakota, South Dakota, Wyoming, California, Nevada, Utah, Colorado, Arizona, New Mexico, Texas. Mexico - Baja California.

Habitat
High elevation coniferous forest, shaded grassy slopes with pines or grasslands, pinyon-juniper and cool desert habitats.

Abundance
Common

Idaho
Cole (1934): This ant is rather frequent in moist habitats near Twin Falls, Hagerman and Buhl, chiefly along the Snake River. Colonies are small, the workers timid and sluggish and the brood scant. Winged forms appear at Twin Falls in late September.

Nevada
Wheeler and Wheeler (1986): In Nevada Temnothorax rugatulus records are widely scattered, but absent from the southern quarter of the state. We have 30 records from 20 localities; 4,700-9,100 ft., mostly 6,000-7,000 ft. Fifteen records were from the Coniferous Forest Biome, 5 from the Pinyon-Juniper Biome, and 4 from the Cool Desert. Five nests were under stones, 8 were in rotten wood. This is a slow-moving ant.

New Mexico
Cole (1953, 1954): Colonies of Temnothorax rugatulus Emery were observed at an elevation of 6,350 ft. at Bandelier National Monument and 5 mi. E. of Taos, 7,350 ft. At both places nests were common beneath stones on shaded grassy slopes with pines. A number of the colonies was very populous and multiple queens were present.

Foraging/Diet
An interesting study of starvation resistance by Ruppel and Kirkman (2005) showed the following interesting findings.

Most of a set of 21 laboratory colonies were able to survive eight months without any food. Brood decline began first (after two months) and mortality was highest, worker decline was intermediate, and queen mortality started latest and remained lowest. Brood (its relative change during the first four months and the level of brood relative to colony size) was the only significant predictor of colony starvation resistance.

Most colonies survived four months of total starvation without a significant decline. While it was found that the number of brood and workers was dramatically reduced after eight months, this time period exceeds the annual period of productive warm weather activity in most Temnothorax rugatulus habitats.

From this study they conclude that most well-fed colonies could survive a whole season without food. Internal resources and brood are suggested to be the only effective mediators of starvation resistance in this species. The amount of brood continued to increase during the first two months without food, with the brood then becoming a source of nutrients once internal reserves were depleted. Colony size was not shown to provide does not confer any survival advantage.

Colony Attributes
Colony size averaged from 54 to 141 workers (15 subpopulations), with a significant difference between pologyne (91±85 (SD)) and monogyne colonies (65±42). (Rüppell et al. 2001)

Moglich (1978) studying a population of Temnothorax rugatulus in a mixed oak-juniper forest in the Chiricahua Mountains found colonies had an average of 109 workers (range 30 to over 200).

Males fat stores were found to be 10.1±9.0 (SD) μg, n=40; macrogyne fat stores 466.4±146.9 μg, n=35; microgynes fat stores 51.4±12.3 μg, n=10. Relative fat content was not correlated with head width in microgynes (rp=–0.19, P=0.60), but was in macrogynes (rp=0.42, P=0.01).(Rüppell et al. 2001)

Nesting Biology
Nests have been found in the soil, under and between rocks, in decaying wood, in grasses and in trees. Colonies will readily emigrate to new nest locations if a nest or micro-ecological conditions become unfavorable.

Moglich (1978) studying a population of Temnothorax rugatulus in a mixed oak-juniper forest in the Chiricahua Mountains described their nests, which were found under stones. Dry brown oak leaves, juniper needles, little twigs and a diversity of other plant materials formed the bases of the nest chambers, which showed flat, often unbroken surfaces. Thus the whole colony was exposed after the stone was turned. The ants were crowded together either on the top of the material or upside down on the stone ceiling. Sometimes, however, a few small chambers were built into the base of the nest. Although the space covered by the rock measured 219 x 292 cm2 (range 32-1 800 cm2) the nest chambers were considerably smaller (24 x 17 cm2; range 2.4-63 cm2). The walls confining the nest chambers were constructed out of fine material like soil and small vegetation particles. Mean nest density was 1.5 ± 0.9 per 9.3 m2).

Reproduction
There are two queen morphs in Leptothorax rugatulus. Microgynes, slightly larger than worker size, and macrogynes, which are roughly twice as large as workers. Genetic evidence shows that queens in polygynous colonies are related to each other, supporting the hypothesis that colonies with more than one queen commonly arise by the adoption of daughter queens into their natal colonies. The higher fat content of macrogynes, their predominance in monogynous societies and in small founding colonies, and their greater flight activity favor the view that macrogynes predominantly found colonies independently, while microgynes are specialized for dependent colony founding by readoption. Despite the potential for these two mating strategies to lead to the creation of distinctive genetic subpopulations, genetic diversity is likely maintained by queens mating randomly with males. (Rüppell et al. 1998, Rüppell et al. 2001, Rüppell et al. 2003)

Nest Migration
Temnothorax rugatulus use both tandem running and carrying behavior during nest emigration. Tandem running is strictly limited to the first phase of nest emigration, whereas carrying behavior is the predominant technique (84 %). Workers which are recruited by tandem running inspect the new nest site. If they accept it, they join the scout force and lead or carry nestmates to the new nest by themselves. (Moglich 1978)

Other Insects
Amecocerus sp. (Coleoptera: Melyridae; det. J.M. Kingsolver) was taken in a nest of Peavine Peak (Washoe Co.) at 6,800 ft. (Wheeler and Wheeler 1986)

Cysticercoids of a dilepidid cestode were found by dissection of aberrant yellowish workers and virgin queens of the ant Leptothorax rugatulus from several mountain ranges in the southwestern United States. The cestode was not positively identified, but cysticercoids are similar to those of the genus Anomotaenia previously found in related ants. (Heinze et al. 1998)

Queen
There are two queen forms, microgynes and macrogynes.

Worker
Testacea, capite abdomineque magis minusve (uscatis, capite thoraceque dense punctatis et cum rugis subtilibus longitudinalibus,antennis 11 articulatis, thorace breviusculo, dorso haud impresso, spinis vix curvatis, obliquis, mediocribus, acutis; petioli segmento 1. postice modice incrassato, 2. subtrapezoideo, scapo pedibusque haud pilosis.

Queen
Queens are known for this species but they have not been described.

Male
Males are known for this species but they have not been described.

Type Material
AMNH,MCSN (as reported in Mackay 2000)

Type Locality Information
The original description lists specimens from Colorado and South Dakota. Creighton (1950) gives the type locality as Colorado "by present restriction."

Etymology
Morphology. A reference to the rugosity found on the body.