Polyrhachis laboriosa

Identification
A member of the Polyrhachis militaris species-group.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Cameroun, Congo, Democratic Republic of Congo, Equatorial Guinea, Ghana, Ivory Coast, Nigeria, Sierra Leone, Togo, Uganda.

Biology
P. laboriosa lives in pioneer trees and shrubs on forest edges in west Africa (Lenoir & Dejean 1994). Nests are built at a height of 2-3m in the canopy of small trees, using living leaves and plant debris. There is great diversity in the architecture of these nests, showing high opportunism by the ants. Leaves are often incorporated in the nests, and provide structural strength for the carton. P. laboriosa belongs to the subgenus Myrma, in which there is no weaving using larval silk. The use of spider silk for nest construction has been described for P. laboriosa (Collart 1932). J.-L. Mercier (unpublished) observed a worker collecting silk from a spider web on a leaf surface. The ant pulled on the silk strands one by one, and rolled them into a ball using her gaster. During this time, the spider stood about 5cm away, and once attempted to chase the ant. At the end, the worker carried the silk to her nest that was being constructed by about 10 nestmates.

Founding queens have been observed retrieving various vegetal material which was used to build a small cell under a leaf (Lenoir & Dejean 1994). Two of 18 foundations involved two queens.

Foraging for plant secretions and small prey or insect corpses is done mostly by single workers orientating visually, although chemical recruitment occurs when larger food sources are exploited (Mercier & Lenoir 1999).

61 nests censused near Yaoundé (Cameroon) yielded an average of 400 workers per nest (range 25-1919). Only 21% of nests had a dealated fertile queen, and such nests were more populous (881±505 workers, N=12) than queenless nests (277.5±263 workers, N=44) (J.-L. Mercier, unpublished). Five nests collected in Dja Reserve (Cameroon) contained 63-457 workers and up to 259 worker cocoons; a dealate queen was present in only one nest (K. Yéo & C. Peeters, unpublished). These data support the idea that P. laboriosa colonies are polydomous (i.e. distributed into several nests) and monogynous (single queen).



Castes






Nomenclature

 *  laboriosa. Polyrhachis laboriosus Smith, F. 1858b: 72, pl. 4, figs. 21, 22 (w.) SIERRA LEONE. Mayr, 1896: 250 (q.m.); Wheeler, G.C. & Wheeler, J. 1953e: 207 (l.). Combination in P. (Myrma): Santschi, 1914d: 384. Senior synonym of architecta, hortulana: Bolton, 1973b: 308.
 * architecta. Polyrhachis (Myrma) laboriosa var. architecta Santschi, 1924b: 224 (w.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of laboriosa: Bolton, 1973b: 308.
 * hortulana. Polyrhachis (Myrma) hortulana Arnold, 1955: 735, fig. 3 (w.) UGANDA. Junior synonym of laboriosa: Bolton, 1973b: 308.