Slave-making ant (Harpagoxenus sublaevis)
|Size||Worker length: 4 - 6 mm length (2)|
Harpagoxenus sublaevis is classified as Vulnerable (VU) on the IUCN Red List (1).
Harpagoxenus sublaevis is a ‘slave-making ant’ – an ant which enslaves ants of other species to provide workers for its own colony. Like all Harpagoxenus species, Harpagoxenus sublaevis workers (wingless females) are small with dark brown, hairy bodies and short legs, but can be distinguished from other species by the large, wide, rectangular head and toothless mandibles (3) (4). Queen (reproductive female) slave-making ants are well adapted to their parasitic lifestyle, having strong mandibles and a very thick cuticle (5). Unlike many ant species, in which the queens are able to fly, the majority of Harpagoxenus sublaevis queens are wingless (5) (6).
Harpagoxenus sublaevis is found in Europe. Its range extends from the Pyrenees eastwards to Russia, and from the north of Italy to northern Norway (7).
Harpagoxenus sublaevis occurs in mountainous regions up to 2,400 metres above sea level. It is mostly found under rock cover but has also been found in subalpine meadows, bogs, marshland, rocky slopes, dry woods, in rotten logs and under tree bark (7).
Harpagoxenus sublaevis has a remarkable life history. Unlike other ant species, in which the worker ants (wingless females) undertake tasks such as searching for food and defending the nest, Harpagoxenus sublaevis ants enslave Leptothorax ants to do this work instead (8) (9) (10).
This begins when a wingless virgin queen climbs a vertical structure in the vicinity of the nest and releases a sexual pheromone which attracts males and stimulates them to mate (10). Once mated, the queen searches for a Leptothorax nest within walking distance to invade (6).
The queen attacks the Leptothorax colony by using her mandibles like secateurs to dismember defending workers, and also deploys what could be described as a ‘chemical weapon’; the queen secretes a sticky substance which, when smeared on Leptothorax workers, causes the defending workers to attack each other. The substance somehow results in the contaminated worker, and not the slave-maker queen, being perceived as the enemy. As the substance is sticky, it quickly spreads from worker to worker, enabling the queen to slip past the growing chaos to begin her final assault on the Leptothorax queen (9). Once all adult Leptothorax ants have been killed or driven away, the Harpagoxenus sublaevis queen remains with the Leptothorax brood. When the brood hatches, these new workers accept the Harpagoxenus sublaevis queen as their own, and start undertaking all routine tasks such as foraging, nest building and caring for the queen’s new brood. The Harpagoxenus sublaevis workers that hatch from this brood specialise in raiding new nests to refresh the ‘slave’ worker force (6) (11).
A Harpagoxenus sublaevis ‘scout’ locates a Leptothorax nest and then returns to its own nest to recruit a nest mate by releasing special pheromones from its abdomen. The recruited member will then follow the scout back to the host species nest. Once there, either the scout or the newly recruited ant will again return to its own nest and recruit another worker. This occurs until a sufficient number of workers have assembled to lay siege to the host colony (8).
In a similar manner to how the queen invaded a Leptothorax colony, the Harpagoxenus workers use their mandibles to clip the legs and antennae of the host defenders, and secrete a substance that provokes internal battles among the Leptothorax workers (9). Once the siege is over, the host eggs and larvae are eaten and the pupae are removed and returned to the Harpagoxenus sublaevis colony (8). The Leptothorax workers that emerge from this stolen brood then undertake foraging, nest-building, and caring for the brood for Harpagoxenus sublaevis (8) (11). Harpagoxenus sublaevis undertakes any reproductive activity and slave raids during the summer (10).
Unlike many other ant species, Harpagoxenus sublaevis workers are capable of producing viable sons from unfertilised eggs. However, the queen, who would prefer workers to be exclusively putting energy into her young, uses chemical secretions to inhibit the workers’ reproduction. Harpagoxenus sublaevis workers probably only reproduce after the death of the queen (9).
While Harpagoxenus sublaevis is considered threatened by the IUCN Red List (1), it is not clear what threats this ant faces.
No conservation measures are currently known to be in place for Harpagoxenus sublaevis.
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- Cuticle: the outer layer of the external skeleton of the ant.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ scientific species name; the second part is the specific name.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Mandibles: the pair of mouthparts most commonly used for seizing and cutting food, common to the centipedes, millipedes and insects.
- Parasitic: describes an organism that derives its food from, and lives in or on, another living organism at the host’s expense.
- Pheromone: a chemical produced by an animal, which stimulates a behavioural or physiological response by another member of the same species.
- Pupae: stage in an insect’s development when huge changes occur, which reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
IUCN Red List (October, 2010)
AntWeb - Harpagoxenus sublaevis (October, 2010)
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- Wheeler, W.M. (1910) Ants: their Structure, Development and Behaviour. Columbia University Press, New York.
- Brandt, M., Foitzik, S., Fischer-Blass, B. and Heinze, J. (2005) The coevolutionary dynamics of obligate ant social parasite systems - between prudence and antagonism. Biological Review, 80: 251-267.
- Bauer, S.M.V. (2009) Coevolutionary Dynamics and Geographic Mosaics in the Social Parasite Harpagoxenus sublaevis and its Two Host Species. Dissertation, Ludwig-Maximilians-Universität, München.
- Antonova, V. (2009) First record of the slave-maker ant Harpagoxenus sublaevis (Nylander, 1849) from Bulgaria (Hymenoptera: Formicidae). Myrmecological News, 12: 1-2.
- Hӧlldobler, B. and Wilson, E.O. (1990) The Ants. Springer, Berlin.
- Franks, N. and Bourke, A. (1988) Slaves of circumstance. New Scientist, 1627: 45-49.
- Buschinger, A. (1983) Sexual behaviour and slave raiding of the dulotic ant, Harpagoxenus sublaevis (NYL.) under field conditions (Hym. Formicidae). Insectes Sociaux, 30(3): 235-240.
- Bourke, A.F.G. (1988) Dominance orders, worker reproduction, and queen-worker conflict in the slave-making ant Harpagoxenus sublaevis. Behavioural Ecology and Sociobiology, 23: 323-333.