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Anoplolepis gracilipes (Family Formicidae)

Yellow Crazy Ant, Gramang Ant, Long-legged Ant, Maldive Ant

Distribution:

The centre of diversity for the genus Anoplolepis is Africa and A. gracilipes is the only species distributed beyond that continent. It has been widely introduced through human commerce and trade across the subtropics and tropics, including East Africa, South and South-east Asia, Melanesia, and the Indo-Pacific Islands. In Australia, A. gracilipes has spread across approximately 2500 km² in the Northern Territory. Recent incursions have been reported in tropical and subtropical Australia (Cairns, Townsville, Brisbane). It is capable of invading both disturbed and undisturbed habitats, including tropical urban areas, plantations, grassland, savannah, woodland, and rainforest. (QLD, NT, Christmas Is; Cocos-Keeling Is.)

Features:

Anoplolepis gracilipes is notable for its remarkably long legs and antennae (hence the common name, long–legged ant) as well as its frenetic behaviour when disturbed (hence the name, crazy ant). Adults are yellow-brownish with a long slender (i.e. gracile) body, and approximately 4–5 mm long. Lacks a sting but subdues and kills prey by spraying formic acid.

Ecology/Way of Life:

Anoplolepis gracilipes is a well-known tramp ant species. It is multi-queened and forms diffuse “supercolonies”, sometimes extending over large areas (10–150 ha). Single nests can contain upwards of 300 queens and 2 500–36 000 workers. Most dispersal and colony foundation occurs through colony budding; mating flights have not been reported. Worker production is continuous throughout the year and initiation of sexual brood usually follows the onset of the wet season. The life cycle of A. gracilipes has been estimated to take 76–84 days. Anoplolepis gracilipes has a broad diet and preys on a variety of litter and canopy fauna, from small isopods, myriapods, molluscs, arachnids, and insects to large land crabs, birds, mammals, and reptiles. In addition to these protein-rich foods, A. gracilipes obtains carbohydrates and amino acids through its association with honeydew-secreting Homoptera, which it tends on stems and leaves of a wide variety of plants.

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Interaction with Humans/Threats:

Anoplolepis gracilipes is a major environmental pest and is recognized as one of the world's worst invaders. Where densities are high, impacts can occur on native 'keystone' species as well as endemic reptiles, birds, and mammals. This can alter community structure and species composition, and affect ecosystem processes including litter decomposition. On Christmas Island, Indian Ocean, deletion of the native red land crab by A. gracilipes causes a rapid state change in native communities. Association of A. gracilipes with honeydew-secreting Homoptera can cause population outbreaks of these sap-sucking insects and lead to forest dieback. Secondary invasions of giant African landsnails and woody weeds can follow invasion by A. gracilipes, further degrading native forests. In crops, negative impacts occur through increased populations of Homoptera, although some believe that this ant benefits crop plants by deterring plant pests. A. gracilipes commonly nests at the base of plants, sometimes undermining crops such as sugarcane and coffee. In some instances, A. gracilipes is a household and rural pest. Formic acid sprayed by the ants can cause skin burns and irritate the eyes of fieldworkers. A control program administered by Parks Australia North is currently underway on Christmas Island, Indian Ocean.

Further Reading:

The IUCN/SSC Invasive Species Specialist Group (ISSG). (2005). Global Invasive Species Database. www.issg.org/database

Shattuck, S.O. & Barnett, N.J. (2001). Australian Ants On-line. http://www.ento.csiro.au/science/ants/

Japanese Ant Database Group. (2003). Japanese Ant Image Database. http://ant.edb.miyakyo-u.ac.jp/E/index.html

Green, P., O'Dowd, D. & Lake, P.S. (2000). Ecosystem collapse on an oceanic island following alien ant invasion. Aliens 9: pp2–4.

Acknowledgments:

Text, map and photographs by Dennis O'Dowd.

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Images and Multi-media:  
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image/gif 59821 bytes Anoplolepis gracilipes
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image/gif 61543 bytes Anoplolepis gracilipes attacking a crab
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image/gif 43948 bytes Anoplolepis gracilipes structure

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