Monomorium exiguum has been found across central and southern Africa, from Ethiopia in the east to Guinea in the west and Zimbabwe in the south. It appears to be primarily a forest species, so it is no surprise that the Gambian specimens were collected from a tree in Abuko National Park, one of the few remaining patches of gallery forest.
Bolton (1987) states that M. exiguum as defined definitely contains more than one valid species, but could not resolve them. It is therefore interesting to note the small size of the Gambian specimens, which are apparently much smaller than is typical for the species; Bolton gives lengths of 1.5-1.7 mm whereas the Gambian specimens can be little more than 1 mm long.
These have been compared with specimens checked by Bolton at the Natural History Museum, London, and are confirmed as M. exiguum.