Temnothorax congruus

This is an arboreal species, nesting in dead twigs of standing trees. Nuptial flights occur in mid July (Sonobe, 1980). The chromosome number is 2n = 18 (Imai & Kubota, 1972). It is common in Honshu, Shikoku, and Kyushu, but rare in Hokkaido.

Identification
Radchenko (2004) - T. congruus is a small blackish-brown species with short propodeal spines. It most resembles Temnothorax wui and differs from it by the shape of the petiole, whose node has a wide, slightly convex dorsal plate (in T. wui the petiolar node is very narrowly rounded, subtriangular in profile); the sculpture of the head dorsum: frons with longitudinal rugae and coarse punctures, remaining parts punctate (in T. wui the whole head dorsum finely and densely punctate, striated only near the eyes; the central part of frons with a smooth and shiny longitudinal band). T. congruus differs from Temnothorax kurilensis by its much shorter antennal scape, which distinctly fails to reach the occipital margin, SI1 < 0.73, SI2 < 0.90 (in the latter species the scape almost reaches or slightly surpasses the occipital margin, SI1 > 0.75, SI2 > 0.94), and by the shorter propodeal spines.

Terayama and Onoyama (1999) - Total length of workers around 2.5-3 mm. Body color black to blackish brown. Scapes short, not reaching posterior margin of head. Dorsal outline of mesosoma almost straight in profile. Propodeum with short, triangular spines of variable size. Petiolar node triangular, its dorsal margin angulate in profile.

T. congruus is distinguished from other Japanese Temnothorax species by the black body, the short scapes, and the short propodeal spines.

Distribution based on Regional Taxon Lists
Palaearctic Region: China, Democratic Peoples Republic of Korea, Japan, Republic of Korea, Russian Federation.

Biology
Syoji and Eguchi (2017) - This species is widespread in Japan, usually inhabiting forest edges, bushes and gardens. They nest inside hollow dead branches and dead grass stems. They examined nest choice in laboratory experiments:

using Temnothorax congruus and its putative sympatric competitor Crematogaster teranishii we investigated whether nesting site selection by T. congruus is affected by the presence of C. teranishii.

All of the T. congruous colonies (n=93, found in stems of Hydrangea sp. and bamboo grass) were queenright; the median number of the workers and larvae + pupae per a T. congruous colony was 59 (interquartile range: 39 to 80) and 58 (interquartile range: 35 to 88), respectively. Experimental results suggested that T. congruus colonies prefer straws that are narrow and have a small number of entrances, which may provide defensive and survival advantages to the colonies. In nature, tube-like structures such as dead branches/stems of Hydrangea spp. and bamboo grass often have many holes and cracks. In nature, stems of bamboo grass nests have only one entrance and T. congruus colonies build collars to reduce the entrance size. Using structures containing holes may increase the risks of desiccation (Bollazzi and Roces 2007) and/or invasion by intra and interspecific competitors (Franks & Partridge 1993) and may require additional costs for maintaining/repairing the nest (Franks 1992). Thus, the fitness of T. congruus colonies may be improved by evaluating the quality of tube-like structures and avoiding low-quality ones.

In the presence of C. teranishii, T. congruous colonies clearly avoided tubes near the C. teranishii nests as their nesting site, even if the tubes near C. teranishii nests were higher in quality than those far from C. teranishii nests. The mortality rate of T. congruus adults was higher in the presence of C. teranishii adults than in the absence of them.

Nomenclature

 *  congruus. Leptothorax congruus Smith, F. 1874: 406 (w.) JAPAN. Wheeler, W.M. 1906c: 317 (q.); Wheeler, G.C. & Wheeler, J. 1955b: 24 (l.); Imai & Kubota, 1972: 197 (k.). Combination in Temnothorax: Bolton, 2003: 271. See also: Terayama & Onoyama, 1999: 83.

Determination Clarifications
Radchenko (2004) - The specimens from North Korea, determined by Collingwood (1976) as T. congruus, are in fact Vollenhovia emeryi Wheeler (material is in, examined).