Short description of Linepithema humile, Argentine ant

Argentine ant workers are monomorphic.  Small (body length is 2-3 mm), medium to dark brown ants with smooth, hairless head, thorax and abdomen.  The petiole comprises a single (scale-like) segment.  Similar to Iridomyrmex species in body shape and colour but differs in the number of teeth on the mandibles, a more pronounced tear-shaped head and lower placement of the eyes. No sting.  No soldier caste. 

Impact summary: Linepithema humile, Argentine ant

Workers can reach high densities (supercolonies) and as such the Argentine ant can be a human nuisance and because it is also a dominant ant and aggressive competitor it has displaced native ant species in many invaded regions of the world, even causing local extinction of some ant species.  The displacement of native ants can disrupt natural ecosystem processes such as soil processes (where ants act as engineers), pollination and seed burial.  

Habitat summary: Linepithema humile, Argentine ant

Regularly or recently cultivated agricultural, horticultural and domestic habitats.  Additionally deciduous and coniferous woodland; preferably associated with disturbed, human-modified habitats in its introduced range, but may also invade natural habitats (e.g., oak and pine woodland in the Mediterranean).

Overview table

Environment	Terrestrial
Species status	Non-Native
Native range	Brazil, Argentina Distrito Federal, Paraguay, Uruguay
Functional type	Omnivore
Status in England	Non-Native
Status in Scotland
Status in Wales
Location of first record	Fulham, West London
Date of first record	2013

Origin

South America (Argentina, Brazil, Paraguay, Uruguay).

First Record

1927 Windsor Forest, England.

Pathway and Method

Transported with vehicles (airplanes, ships) together with imported goods, soil and plants.

Species Status

The species occurs throughout the world on all continents, especially in mediterranean-type climates, and many oceanic islands.  Ecological niche models predict that with changing climate the species will expand at higher latitudes. A recent horizon scanning exercise highlighted the potential for this species to arrive within GB in the next ten years (Roy et al., 2014).

Dispersal Mechanisms

Natural dispersal (non-biotic): Colonies reproduce by diffusion or “budding” (colony expands and radiates outwards eventually forming new satellite colonies).  Winged dispersal of female reproductive forms is rare and this limits natural long distance spread.  Linepithema humile can spread locally by rafting downstream and also form rafts in response to flooding which contributes to dispersal.  However, in general long distance movement of this species is largely dependent on anthropogenic practices.  Trails can often be found ascending from flowering trees and shrubs. Nests are located under wood, stones, piles of leaves in potted plants.   

Anthropogenic practices: In tropical or cold climates L. humile persists in glasshouses or other climate-controlled buildings.  Linepithema humile routinely move their nests and colonise potted plants and refuse; this can facilitate dispersal through subsequent human movement of the material.  Linepithema humile can be transported as small nest fragments on land vehicles and in sea freight.  One queen and ten workers are considered the lower limit for colony establishment.

Reproduction

Haplodiploid, sexual, polygynous. The adult reproductive males are winged and larger than the workers but much smaller than the winged queens.  Fertilisation of new queens takes place in the nest and the new queens lose their wings and walk with the workers to establish new nests.  It has been estimated that populations can spread at a rate of more than 200 m per year.

Workers of all invasive ants are sterile but, each year, in an introduced range, workers kill 90 % of the queens in their colony just prior to the production of new reproductives.  It is thought that this behaviour increases within colony relatedness, promoting social cohesion.  In the absence of a queen L. humile workers can produce eggs. 

Known Predators/Herbivores

Pseudacteon spp. (Diptera: Phoridae) attack L. humile in Brazil and deter ants foraging during the phorid activity period. There is a known nematode Diploscapter lycostoma. 

Resistant Stages

None known.

Habitat Occupied in GB

Linepithema humile have been predominantly found in urban areas and only on the margins of natural habitats so their potential impact on native systems remains unknown, although forest habitats are unlikely to be utilised. 

Not established in GB.

Environmental Impact

Workers can reach high densities (supercolonies) and Argentine ants are dominant and aggressive competitors that have displaced native ant species in many invaded regions of the world, even causing local extinction of some ant species.  The displacement of native ants can disrupt natural ecosystem processes such as soil processes (where ants act as engineers), pollination (this ant also competes for nectar resources) and seed burial (Argentine ants do not bury seeds and in South Africa have been shown to displace two seed burying ant species). 

Health and Social Impact

Large numbers are considered a household nuisance and ants will diffuse into food containers.  Some people are sensitive to the bite of this ant. 

Economic Impact

Economic costs are considered to be low but disruption to ecosystem services could contribute to economic losses.  Argentine ants tend pest homoptera and protect them from natural enemies, therefore, causing increased crop damage. 

Identification

Donisthorpe, H. (1930) The ants (Formicidae) and guests (myrmecophiles) of Windsor Forest and District. Entomol. Record J. Var., 42, 13-16.

http:www.landcareresearch.co.nzresearchbioconsinvertebratesAntsinfosheetslinhum_info.asp

Biology, ecology, spread, vectors

Giraud, T., Pedersen, J.S., Keller, J. (2002) Evolution of supercolonies: The Argentine ants of southern Europe. Proceedings of the National Academy of Sciences of the United States of America, 99, 6075-6079.

Human, K.G., Weiss, S., Weiss, A., Sandler, B., Gordon, D.M. (1998) Effects of abiotic factors on the distribution and activity of the invasive Argentine ant (Hymenoptera, Formicidae). Environmental Entomology, 27, 822–833.

Suarez, A.V., Holway, D.A., Case, T.J. (2001) Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from Argentine ants. Proceedings of the National Academy of Sciences of the United States of America, 98, 1095–1100.

Management and impact

Holway, D.A. (1998) Effect of Argentine ant invasions on ground-dwelling arthropods in northern California riparian woodlands. Oecologia, 116, 252–258. 

Holway, D.A. (1999) Competitive mechanisms underlying the displacement of native ants by the invasive Argentine ant. Ecology, 80, 238–251. 

Human, K.G., Gordon, D.M. (1996) Exploitation and interference competition between the invasive Argentine ant, Linepithema humile, and native ant species. Oecologia, 105, 405–412.

Orr, M.R. & Seike, S.H. (1998) Parasitoids deter foraging by Argentine ants (Linepithema humile) in their native habitat in Brazil. Oecologia, 117, 420–425.

General

Holway, D.A., Lach, L., Suarez, A.V., Tsutsui, N.D., Case, T.J. (2002) The causes and consequences of ant invasions. Annual Review of Ecology and Systematics 33, 181-233

Roy, H.E., Peyton, J., Aldridge, D.C., Bantock, T., Blackburn, T.M., Britton, R., Clark, P., Cook, E., Dehnen-Schmutz, K., Dines, T., Dobson, M., Edwards, F., Harrower, C., Harvey, M.C., Minchin, D., Noble, D.G., Parrott, D., Pocock, M.J.O., Preston, C.D., Roy, S., Salisbury, A., Schönrogge, K., Sewell, J., Shaw, R.H., Stebbing, P., Stewart, A.J.A. and Walker, K.J.(2014) Horizon Scanning for Invasive Non-Native Species in Britain. Global Change Biology 20, 3859-3871.