Rossomrymex  (Rossomyrmex minuchae)

Rossomyrmex minuchae is classified as Vulnerable (VU) on the IUCN Red List (1).

Rossomyrmex minuchae is an extremely rare ‘slave-making ant’ – an ant which enslaves ants of other species to provide workers for its own colony (3). It is one of four species of the Rossomyrmex genus, all of which are similar in appearance. Rossomyrmex ants are black or dark brown in colouration with bright red, well-developed mandibles. The thorax is shiny and polished, but also covered in hairs. These hairs are much sparser on Rossomyrmex minuchae than the other three Rossomyrmex species (2) (4).

Rossomyrmex minuchae is found only in south-western Spain, where only three populations are currently known: in Sierra Nevada, Sierra de Gador and Sierra de Filabres (5).

All three populations of Rossomyrmex minuchae are located high in the mountains, between 1,900 and 2,100 metres above sea level (5), in sclerophyll thorn scrub (6).

Rossomyrmex minuchae has a remarkable life history. Unlike other ant species, in which the worker ants (wingless, sterile females) undertake tasks such as searching for food and defending the nest, worker Rossomyrmex minuchae ants enslave another ant species to do this work instead (3) (7). Proformica longiseta, another ant endemic to the mountains of southern Spain, is the unfortunate species that is enslaved by Rossomyrmex minuchae (8).

Rossomyrmex minuchaeis only active outside of its nest for two months each year, between late June and early August. During this period, Rossomyrmex minuchae workers first scout for a nest of Proformica longiseta; once found, around 60 to 90 Rossomyrmex minuchae gather by the target nest and the invasion begins, with some ants invading through the main entrance while others dig into the nest. A struggle between the two ant species is presumed to take place within the nest, and results in Rossomyrmex minuchae carrying Proformica longiseta pupae, larvae, eggs and small workers back to their own nest. When the pupae hatch, they accept the Rossomyrmex minuchae nest as their own and forage for Rossomyrmex minuchae and care for its brood (3) (6) (7).

All reproductive activity of Rossomyrmex minuchae also takes place within this very short period of annual activity, typically for three weeks during July and August. The mating strategy of this species is characterised by two activity periods. During the ‘mating period’, females call in order to attract males, mate, then return to the nest in which they were born. During the ‘dispersal period’, mated females fly from the nest in search of a new non-parasitized Proformica longiseta nest (8), where they eliminate and replace the Proformica longiseta queen. In this parasitized nest, the Proformica longiseta workers care for the slave-maker (Rossomyrmex minuchae) brood and perform other nest duties, while the slave-making workers specialise in raiding new nests to refresh the worker force (9) (10).

The suitable habitat range of Rossomyrmex minuchae is very small, as this rare ant is highly sensitive to changes in temperature, soil composition and sunlight levels (7). The reforestation of pine (or another tree) in the area inhabited by Rossomyrmex minuchae would greatly alter this specific habitat (6), with possible devastating impacts on the species. In addition, in some areas this habitat has been ploughed, or is at risk from the widening of roads or the planting of crops (6).

Although genetic variation is high between the three separate Rossomyrmex minuchae populations, within each population genetic variation is very low, because there is a low number of sexually reproductive individuals produced each year and limited dispersal of both males and females (5).Low genetic variation limits a population’s ability to adapt to changes in its environment, such as exposure to a new disease, and results in a greater risk of extinction.

Rossomyrmex minuchae occurs in the Sierra Nevada National Park and the Natural Park of Sierra de Gador (6), which should hopefully offer some protection to this species’ habitat. It has been recommended that all populations of Rossomyrmex minuchae should be protected, and that the proposed extension of a road that passes the Sierra Nevada populations is prevented (6).

To learn more about the conservation of ants and other insects see:

• The Xerces Society:
  http://www.xerces.org/
• Buglife:
  http://www.buglife.org.uk/