Slave-making ant  (Chalepoxenus muellerianus)

Classified as Vulnerable (VU) on the IUCN Red List (1).

Chalepoxenus muellerianus is a fascinating ‘slave-making ant’, so named because of its curious behaviour whereby it enslaves other species of ant to perform the work of the colony (3).

Chalepoxenus muellerianus is generally yellowish-brown and its body and legs are covered with fine erect hairs (4). Wrinkles can be found over its entire body, with the exception of the final segment, called the gaster, which is smooth and shiny (5).

Like all ants, Chalepoxenus muellerianus has a short, truncated waist segment, or petiole, which connects the middle body section to the final segment (5). Chalepoxenus muellerianus has a rounded petiole, and the postpetiole segment, found between the petiole and gaster, is virtually absent (4).

Chalepoxenus muellerianus is one of the most common slave-making ants in Europe and is predominantly found in southern parts of the continent (6). It has a wide distribution in the Mediterranean region (7), ranging from Spain and southern France, to Italy, Croatia and as far east as Turkey (4).

Colonies of Chalepoxenus muellerianus usually inhabit mountainous regions, and can be found in rock crevices, often in close proximity to woodland (7). Chalepoxenus muellerianus nests have been found in dry sticks in dense woodland, especially in areas containing black pine (Pinus nigra) (8).

Chalepoxenus muellerianus lives at a variety of altitudes (4), from 300 metres in the Vallée d’Ossau, up to 1,400 metres in San Juan de la Pena in the Pyrenees (7).

All ants found within the genus Chalepoxenus are socially parasitic, raiding the nests of closely related Temnothorax species to capture their brood. The captured ants are raised as slaves of the Chalepoxenus ants to carry out the work of the colony (3) (4). Work includes rearing the slave-maker brood, foraging for food and protecting the nest from other invading insects (9).

Chalepoxenus muellerianus predominantly parasitises Temnothorax unifasciatus, although it also parasitises approximately 12 other species of Temnothorax, including T. tuberum and T. recedens (3) (4) (7). A colony will typically consist of a few dozen Chalepoxenus muellerianus individuals and from zero to several hundred host individuals (10).

Slave raids occur throughout the summer and involve several characteristic steps: scouting for host nests, recruitment of workers, fighting the host species and brood transport (11). The queen Chalepoxenus muellerianus selects only the host brood, and has no use for the other host ants (9). Young female Chalepoxenus muellerianus are responsible for gaining access to the host brood, and capture, destroy or evict any host ants using their stingers (4).

Chalepoxenus muellerianus colonies generally tend to exclusively parasitise one species of host, due to imprinting upon the odour of the host species during a very sensitive period of growth. This significantly affects the queens choice of host during colony foundation, and workers almost exclusively raid the nests of host species already working in the slave-makers nest (9) (10).

The specific threats affecting Chalepoxenus muellerianus are unknown. However, in the Pyrenees, socially parasitic ants are threatened by the degradation of the natural habitat, due to forestry and agricultural practices, pesticide treatments and the snowsports industry (7).

No conservation measures are currently known to be in place for Chalepoxenus muellerianus, but it occurs in several protected areas throughout its range, including the Serra da Estrela in Portugal (4) and the Abruzzi National Park in Italy (12).

Further investigation into the Chalepoxenus muellerianus population and behaviour is recommended to help determine exactly how this ant is threatened, and implement measures to protect it (10).

More information on the conservation of ants and other insects:

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