Worldwide spread of the Argentine ant, Linepithema humile (Hymenoptera: Formicidae)

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The Argentine ant, Linepithema humile (MAYR, 1868), originally from subtropical South America, is an important pest in many parts of the world. To evaluate its worldwide distribution and potential for further spread, we mapped records of L. humile from > 2100 sites. Because several South and Central American Linepithema species have been often mis-identified as L. humile, we excluded all unconfirmed South and Central American records. We documented the earliest known L. humile records for 95 geographic areas (countries, island groups, major islands, and US states), including several for which we found no previously published records. We could not confirm any L. humile records from several South and Central American countries with published reports. Most records of L. humile come from the subtropics, particularly from regions with Mediterranean-like climates (i.e., warm dry summers and cool moist winters), including its native range in South America and exotic populations in Cali-fornia, the Mediterranean, southern Africa, Australia, New Zealand, and Japan. In more humid subtropical areas, such as the southeast US, L. humile rarely dominates outside urban areas. In tropical latitudes, L. humile dominates only at higher elevations, most notably in Hawaii. In temperate areas, L. humile is almost exclusively an indoor pest.
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Myrmecological News 12 187-194 Vienna, September 2009
Worldwide spread of the Argentine ant, Linepithema humile (Hymenoptera: Formicidae)
James K. WETTERER, Alexander L. WILD, Andrew V. SUAREZ, Núria ROURA-PASCUAL & Xavier ESPADALER
The Argentine ant, Linepithema humile (MAYR, 1868), originally from subtropical South America, is an important pest
in many parts of the world. To evaluate its worldwide distribution and potential for further spread, we mapped records
of L. humile from > 2100 sites. Because several South and Central American Linepithema species have been often mis-
identified as L. humile, we excluded all unconfirmed South and Central American records. We documented the earliest
known L. humile records for 95 geographic areas (countries, island groups, major islands, and US states), including
several for which we found no previously published records. We could not confirm any L. humile records from several
South and Central American countries with published reports.
Most records of L. humile come from the subtropics, particularly from regions with Mediterranean-like climates (i.e.,
warm dry summers and cool moist winters), including its native range in South America and exotic populations in Cali-
fornia, the Mediterranean, southern Africa, Australia, New Zealand, and Japan. In more humid subtropical areas, such as
the southeast US, L. humile rarely dominates outside urban areas. In tropical latitudes, L. humile dominates only at higher
elevations, most notably in Hawaii. In temperate areas, L. humile is almost exclusively an indoor pest.
Linepithema humile has already spread to most subtropical lowland regions with Mediterranean-like climates, but is not
known yet from most tropical highland areas with suitable climates. In the past, L. humile probably arrived in tropical
regions by sea accompanying human commerce and had to survive coastal lowland conditions before spreading to higher,
cooler elevations. Nowadays air travel allows L. humile to stowaway in cargo delivered almost anywhere in the world.
Therefore, a wider spread of this pest is expected in the future.
Key words: Biogeography, biological invasion, exotic species, Formicidae, invasive species.
Myrmecol. News 12: 187-194 (online 8 June 2009)
ISSN 1994-4136 (print), ISSN 1997-3500 (online)
Received 30 August 2008; revision received 3 March 2009; accepted 4 March 2009
Prof. Dr. James K. Wetterer (contact author), Wilkes Honors College, Florida Atlantic University, 5353 Parkside Drive,
Jupiter, FL 33458, USA. E-mail:
Dr. Alexander L. Wild & Prof. Dr. Andrew V. Suarez, Department of Entomology, University of Illinois, 320 Morrill Hall,
505 S. Goodwin Ave., Urbana, IL 61801, USA. E-mail:;
Dr. Núria Roura-Pascual, Centre for Invasion Biology, Department of Botany & Zoology, Stellenbosch University, Pri-
vate Bag X1, Matieland 7602, South Africa. E-mail:
Prof. Dr. Xavier Espadaler, 2. Ecology Unit, Universidad Autónoma de Barcelona, E-08193 Bellaterra, Spain. E-mail:
Several exotic ant species are known to have substantial
ecological impacts. When these species invade, they can
disrupt the indigenous invertebrate fauna and transform
the native biotic community. Among the most destructive
invasive ants are the red imported fire ant, Solenopsis invicta
BUREN, 1972 (ALLEN & al. 2004), the little fire ant, Was-
mannia auropunctata (ROGER, 1863) (WETTERER & PORTER
2003), the long-legged ant Anoplolepis gracilipes (SMITH,
1857) (WETTERER 2005), the African big-headed ant, Phei-
dole megacephala (FABRICIUS, 1793) (WETTERER 2007),
and the Argentine ant, Linepithema humile (MAYR, 1868)
(VEGA & RUST 2001).
Linepithema humile (Figs. 1 - 4) has negative impacts
on many other animals, both vertebrates and invertebrates
e.g., VEGA & RUST 2001, WETTERER & al. 2001, SUAREZ
& al. 2005). In addition, L. humile can be a significant agri-
cultural pest, enhancing populations of Hemiptera (VEGA &
RUST 2001). Hemiptera cause damage by sapping plants
of nutrients and increasing the occurrence of diseases, in-
cluding viral and fungal infections.
Linepithema humile is native to the Paraná River drain-
age area of subtropical Argentina, Brazil, Paraguay, and
Uruguay, which has a Mediterranean-like climate, i.e., warm
dry summers and cool moist winters (WILD 2004). It has
become a major pest in many areas around the world with
similar climates. Recently, several papers have examined
the worldwide spread of L. humile and predicted its poten-
tial distribution based on current and future climate es-
timates (SUAREZ & al. 2001, HARTLEY & LESTER 2003,
ROURA-PASCUAL & al. 2004, HARTLEY & al. 2006, WARD
Figs. 1 - 4: Linepithema humile. (1) head of worker from Entre Rios, Argentina (specimen ID = CASENT0106983); (2)
lateral view of the same worker; (3) dorsal view of the same worker; (4) worker tending a scale insect in California (photos
by A.L. Wild).
2007). In the present paper, we have documented more
fully the historic spread and current worldwide distribution
of L. humile, and corrected some errors in the literature.
We documented the range of L. humile using both published
and unpublished records. and the FORMIS
bibliography were essential resources for finding relevant
published papers. We obtained unpublished site records
from the collections of American Museum of Natural His-
tory (AMNH), Archbold Biological Station (ABS), the
Natural History Museum, London (BMNH), the California
Academy of Science (CAS), the Field Museum (FM), the
Florida State Arthropod collection (FSAC), the Los Ange-
les Museum of Natural History (LACM), the Museum of
Comparative Zoology (MCZ), the Museo Civico di Storia
Naturale "Giacomo Doria" (MSNG), the Museu de Zoolo-
gia da Universidade de São Paulo (MZSP), the Naturhis-
torisches Museum Wien (NMW), the Oxford University,
Museum of Natural History (OUNH), the Museo de Zoo-
logía, Pontifica Universidad Católica del Ecuador (QCAZ),
the Smithsonian Institute (SI), the University of Arizona
Museum (UAM), and the University of Minnesota Museum
(UMM), and from on-line databases of the Australian Nati-
onal Insect Collection, the California Academy of Science,
Fauna Europaea, the Global Diversity Information Facility,
Landcare Research, the Essig Museum, the Pacific Basin
Information Node, and the Nebraska State Insect Records
(NSIR). We received unpublished site records from E. Bod-
son (Belgium), J. Delabie (Brazil, Chile, Tunisia), R. Guillem
(Gibraltar, Morocco), G. Heller (Canary Islands, Italy, Fran-
ce, Spain), M. Lush (Spain), and P. Pellitteri (Wisconsin).
We also included our own unpublished specimen records.
If a site record listed a geographic region rather than a
"point locale," and we had no other record for this region,
we used the coordinates of the capital or largest town
within the region or, in the case of small islands and nat-
ural areas, the center of the region. Often, if one reference
had many sites less than 10 - 20 km apart (e.g., HUDDLE-
STON & FLUKER 1968), we did not plot every site. We did
not map records of L. humile on boats or intercepted in
transit by quarantine inspectors, though it is possible that we
included some quarantine records that were not labeled as
Because WILD (2007) found many L. humile records
from South and Central America were misidentifications of
other Linepithema species (e.g., Linepithema dispertitum
(FOREL, 1885), Linepithema iniquum (MAYR, 1870), and
Linepithema neotropicum WILD, 2007), we excluded all
South and Central American records not confirmed by
Fig. 5: Worldwide distribution of Linepithema humile.
WILD (2007). In contrast, the only other Linepithema spe-
cies that WILD (2007) recorded from outside South and
Central America were a few L. iniquum records from Bel-
gium (two records), Germany (one record), Ireland (one
record), and Massachusetts (one record). We therefore map-
ped all other L. humile records outside South and Central
America assuming that they were fairly reliable.
We plotted records of L. humile from > 2100 sites around
the world (Fig. 5). These records of L. humile came from
95 different geographic areas (i.e., countries, island groups,
major islands, and US states), including several for which
we found no previously published records: Tunisia, Idaho,
Nebraska, Pennsylvania, and Wisconsin (Tabs. 1 - 6).
We could not confirm any L. humile records from sev-
eral South and Central American countries with published
reports: Costa Rica, El Salvador, Guyana, Surinam, and
Venezuela. WILD (2007) found that many published rec-
ords of L. humile from South and Central America were
actually based on misidentification of other species: e.g.,
Costa Rica (PERFECTO & SNELLING 1995; all records = L.
neotropicum), Venezuela (ROURA-PASCUAL & al. 2004;
only record = L. iniquum), and El Salvador (ROURA-
PASCUAL & al. 2004; only record = L. dispertitum). We
could not find any specimens confirming published L.
humile records from Surinam and Guyana (DÜRR 1952).
We excluded unconfirmed L. humile records from other
South and Central American countries, including several
that predate our earliest confirmed records from those coun-
tries: Brazil (e.g., VON IHERING 1894), Colombia (e.g., FO-
REL 1912), Chile (e.g., NEWELL & BARBER 1913), Mex-
ico (e.g., CARPENTER 1902), and Peru (e.g., DALE 1974).
Originally from subtropical South America, Linepithema
humile began its spread to the greater Mediterranean re-
gion in the 19th century. The earliest known specimen of
L. humile, predating even the type specimens collected in
Tab. 1: Earliest confirmed records of Linepithema humile
from South and Central America. See text for acronyms.
* = see text for earlier unconfirmed published records.
Native range
Earliest confirmed record
Argentina 1866 (MAYR 1868)
Uruguay 1885 (collector unknown; NMW): Monte-
Paraguay 1896 (G. Boggiani; MSNG): Puerto 14
de Mayo
Brazil 1914* (BORGMEIER 1928 as Iridomyrmex
riograndensis BORGMEIER, 1928)
Exotic range
Chile 1965* (A. München; MZSP): Temuco
Mexico 1965* (N. Krauss; BMNH): Mexico City
Colombia 1973* (W.P. Mackay; pers. coll.): Armenia
Peru 1982* (P. Majlut; MZSP): Los Condores
Ecuador 2002 (M.F. Salvador; QCAZ): Quito
Argentina in 1866 (MAYR 1868), was collected on the At-
lantic island of Madeira between 1847 and 1858 (WETTE-
RER & al. 2006). In the 19th century, Madeira was a hub
for commerce between Portugal and its colonies in South
America, and collection records suggest that L. humile
may have first spread through the greater Mediterranean re-
gion via Madeira and Portugal (WETTERER & WETTERER
2006, WETTERER & al. 2006). All of the earliest records
from continental Europe (1890 - 1896) come from Portugal
(SCHMITZ 1897, MARTINS 1907, COUTINHO 1929). Some
50 years after first being collected in Madeira, and 20 years
after being recorded in Portugal, L. humile began appear-
ing in other parts of the greater Mediterranean region (Tab.
2). By the 1920s, L. humile had been collected in two other
Tab. 2: Earliest known records of Linepithema humile from
the greater Mediterranean region and on Atlantic islands.
See text for acronyms. + = no previously published records.
Earliest record
+ Madeira 1858 (WETTERER & al. 2006)
+ Portugal 1890 (MARTINS 1907)
+ Italy 1902 (SILVESTRI 1922)
+ France ~ 1906 (MARCHAL 1917)
+ Canary Islands 1909 (STITZ 1916)
+ Spain 1916 (FRISQUE 1935)
+ Bosnia 1916 (FRISQUE 1935)
+ Azores 1921 (CHOPARD 1921)
+ Monaco 1921 (CHOPARD 1921)
+ Algeria 1923 (FRISQUE 1935)
+ Sicily 1926 (H. Donisthorpe, BMNH):
+ Bermuda 1949 (BENNETT & HUGHES 1959)
+ Balearic Islands 1953 (GÓMEZ & ESPADALER 2006)
+ Morocco 1956 (WETTERER & al. 2006)
+ Greece 1967 (BERNARD 1968)
+ Corsica 1967 (BERNARD 1968)
+ Malta 1968 (BARONI URBANI 1968)
+ Sardinia 1974 (CASEVITZ-WEULERSSE 1974)
+ St Helena 2002 (WETTERER & al. 2007)
+ Bulgaria 2004 (RADCHENKO 2004)
+ Crete 2004 (RADCHENKO 2004)
+ Gibraltar 2004 (RADCHENKO 2004)
+ Tunisia 2005 (J. Delabie, pers comm.):
North Atlantic archipelagos (Canary Islands and Azores)
and from numerous sites in southwestern Europe (Spain,
southern France, and Italy). Later, L. humile began to turn
up in coastal North Africa and the central Mediterranean
(Tab. 2, Fig. 5). Linepithema humile arrived in Bermuda
in the 1940's, and is now the most-dominant ant species
there (WETTERER & WETTERER 2004).
Shortly after appearing in southern Europe, L. humile
began to be reported as an indoor pest in northern Europe
(Tab. 3, Fig. 5). The earliest of these records came from
Belfast, Northern Ireland, where CARPENTER (1902) report-
ed an enormous L. humile population living under the floors
and in the walls of a home. The highest latitude records
come from Sandnes, Norway (58.85° N), where GÓMEZ
& al. (2005) reported L. humile living in two apartments.
Greenhouse records of L. humile are common from many
parts of Europe. Because L. humile can live anywhere that
humans live, there is no limit to the latitude where indoor
populations of this species may be found.
Tab. 3: Earliest known records of Linepithema humile from
western, northern and central Europe.
Earliest record
Ireland (Northern) 1899 (CARPENTER 1902)
Germany 1901 (STITZ 1939)
Belgium 1911 (BONDROIT 1911)
Scotland 1912 (DONISTHORPE 1927)
Poland 1915 (PAX 1915)
England 1915 (DONISTHORPE 1916)
Ireland (Eire) 1921 (CHOPARD 1921)
Guernsey 1927 (DONISTHORPE 1927)
Czech Republic 1947 (NOVÁK 1947)
Austria 1952 (HÖLZEL 1966)
Switzerland 1980 (KUTTER 1981)
Sweden 1995 (DOUWES 1995)
Netherlands 2002 (VIERBERGEN 2003)
Norway 2004 (GÓMEZ & al. 2005)
Linepithema humile arrived in the US in the late 19th
century, where it was first noted in New Orleans (TITUS
1905). It was soon found in subtropical sites across the
Southeast US and California (Tab. 4, Fig. 5). Linepithema
humile now dominates at many urban and riparian sites in
California, and has indoor and greenhouse records scattered
across temperate parts of the US (Tab. 4, Fig. 5), e.g., in the
Desert Dome Exhibit of the Henry Doorly Zoo in Omaha,
Nebraska (2003; NSIR).
In South and Central America, L. humile has extended
its range into temperate and tropical regions (Tab. 1, Fig. 5),
though it is not known as a dominant species in any of these
areas. Many tropical records are from highland areas, e.g.,
around Mexico City (WILD 2004). Most records from ar-
eas with climates less hospitable to L. humile may come
from indoor populations.
Linepithema humile has also been reported from sub-
tropical areas of southern Africa and southern Australia with
Mediterranean-like climates (Tab. 5, Fig. 5), where it has
long been a major widespread pest (CLARK 1941, DÜRR
1952). More recently, L. humile has begun to spread across
subtropical parts of Oceania and Asia, and a few other sub-
tropical locales (Tab. 5).
In tropical Oceania, L. humile is known primarily from
Hawaii (Tab. 6, Fig. 5). COLE & al. (1992) studied the im-
pact of L. humile in the highlands of Maui, where it reaches
elevations up to 2880 m. WETTERER & al. (1998) found L.
humile were common on the dry western slope of Mauna
Kea volcano on the Big Island up to 1680 - 2020 m ele-
vation, but densities quickly dropped off in the cooler areas
above this elevation (maximum elevation 2640 m). Linepi-
thema humile also has records from other tropical locales
(e.g., Indonesia, Cameroon, and Zimbabwe), though these
may be indoor records.
Tab. 4: Earliest known records of Linepithema humile from
US states. See text for acronyms. + = no previously pub-
lished records.
Earliest record
+ Louisiana 1891 (TITUS 1905)
+ Mississippi 1904 (TITUS 1905)
+ California 1905 (SMITH 1936)
+ Illinois 1906 (SMITH 1936)
+ Alabama 1913 (NEWELL & BARBER 1913)
+ Texas 1914 (NEWELL 1914)
+ Florida 1914 (WHEELER 1932)
+ Arkansas 1915 (BARBER 1916)
+ Georgia 1915 (BARBER 1916)
+ North Carolina 1915 (BARBER 1916)
+ South Carolina 1915 (BARBER 1916)
+ Tennessee 1915 (BARBER 1916)
+ Arizona 1922 (collector unknown, UAM):
+ South Dakota 1924 (H.C. Severin, MCZ): Brookings
+ Maryland 1931 (SMITH 1936)
+ Missouri 1933 (SMITH 1936)
+ Virginia 1936 (SMITH 1936)
+ Washington 1938 (R. Gregg, FM): Spokane
+ Minnesota 1941 (collector unknown, UMM):
St. Paul
+ Oregon 1942 (MALLIS 1942)
+ Nevada 1953 (LA RIVERS 1968)
+ Utah 1982 (ALLRED 1982)
+ Nebraska 1983 (A. Tosco, NSIR): Omaha
+ Oklahoma 1992 (ALBRECHT 1995)
+ Ohio 1993 (ARNETT 1993 in COOVERT 2005)
+ Pennsylvania 1993 (KING & GREEN 1994): Philadelphia
+ Michigan 1998 (GULMAHAMAD 1998)
+ New Mexico 2002 (MACKAY & MACKAY 2002)
+ Idaho 2005 (Ventana, SI): Sierra
+ Indiana 2005 (ROBINSON 2005)
+ Wisconsin 2006 (P. Pellitteri, pers. comm.):
Fond du Lac
Future spread
Linepithema humile has already spread to most subtrop-
ical lowland areas around the world with Mediterranean-
like climates, where we would expect its impact would be
Tab. 5: Earliest known records of Linepithema humile from
subtropical parts of sub-Saharan Africa, Asia, Australia,
and Oceania. See text for acronyms.
Earliest record
South Africa 1893 (LOUNSBURY 1909)
Lesotho 1908 (Wroughton, SI): Maseru
Juan Fernandez 1920 (collector unknown, LACM):
site unknown
Australia ~ 1931 (CLARK 1941)
Namibia 1982 (A.C. Marsh, BMNH):
Easter Island 1987 (G. Pauley, SI): Hanga Roa
New Zealand 1990 (GREEN 1990)
Japan 1993 (SUGIYAMA 2000)
United Arab Emirates 1995 (COLLINGWOOD & al. 1997)
North Korea 2005 (RADCHENKO 2005)
Tab. 6: Earliest known records of Linepithema humile from
the Old World tropics. See text for acronyms.
Earliest record
Hawaii 1916 (FRISQUE 1935)
Indonesia 1944 (DONISTHORPE 1950)
Cameroon 1979 (D. Jackson, BMNH): Nkoemvom
Zimbabwe 1986 (FERRER 2000)
Yemen 1998 (COLLINGWOOD & VAN HARTEN 2001)
Philippines 1999 (DAFF 2001)
Malaysia 2000 (NA & LEE 2001)
Vietnam 2005 (RADCHENKO 2005)
the greatest. Within these areas, many populations are still
expanding (e.g., Santa Cruz Island, California, WETTERER
& al. 2001; Japan, OKAUE & al. 2007; New Zealand, WARD
& al. 2005). In some areas, however, populations have de-
clined. For example, on the island of Madeira, L. humile was
once a serious pest, but now it is relatively uncommon, ex-
cept in the semi-arid eastern regions (WETTERER & al. 2006).
Despite BYTINSKI-SALZ's (1952) prediction that L. hu-
mile "must be expected to penetrate the Eastern Mediterra-
nean soon," L. humile has not yet been reported east of
Crete. Linepithema humile also has not yet been reported
from regions of southern China and central Africa that have
appropriate Mediterranean-like climates (ROURA-PASCUAL
& al. 2004, HARTLEY & al. 2006). Although L. humile will
likely spread to other subtropical areas as well (ROURA-
PASCUAL & al. 2004, HARTLEY & al. 2006), it is unlikely
to dominate in more humid areas. The importance of aridity
in determining the dominance of L. humile is well illustrat-
ed on a fine grain scale in the Madeira archipelago, where
L. humile is common in the dry eastern parts, but relatively
rare in wetter areas (WETTERER & al. 2006). Linepithema
humile once was a significant pest across much of the hu-
mid southeastern US, but is now largely restricted to urban
areas (e.g., see BUCZKOWSKI & al. 2004).
Linepithema humile is still largely unknown from trop-
ical highland areas that have suitable climates that might
allow it to dominate. Until recently, most exotic ant species
invading tropical regions probably arrived by sea accom-
panying human commerce. These invaders had to survive
under lowland tropical conditions before spreading to other
locales. This may explain why relatively few ant species
have invaded the cooler highland areas (REIMER 1994).
WILSON & TAYLOR (1967) noted that populations of L.
humile in Hawaii were often associated with army camps
and bivouacs, and concluded that colonies probably were
being transported inadvertently with army supplies and
equipment. Nowadays, air travel allows exotic ants to stow-
away in cargo delivered almost anywhere. The latitudinal
range of L. humile may also increase globally as a result
of climate change (ROURA-PASCUAL & al. 2004).
We thank A. Wetterer and M. Wetterer for comments on this
manuscript; S. Cover for help, encouragement, and ant iden-
tification; P. Pellitteri, M. Lush, G. Heller, R. Guillem, J.
Delabie, and E. Bodson for providing unpublished records;
B. Bolton (BMNH), J. Carpenter (AMNH), P. Clausen
(UMC), S. Cover (MCZ), M. Deyrup (ABS), J. Hogan
(ONHM), G. Knight (NML), and T. Schultz (SI) for help
with their respective ant collections; W. O'Brien for GIS
help; D.P. Wojcik and S.D. Porter for compiling their valu-
able FORMIS bibliography; C. Scheid and R. Pasos of the
FAU library for processing so many interlibrary loans;
Florida Atlantic University, the National Science Founda-
tion, and the National Geographic Society for financial sup-
Die Argentinische Ameise, Linepithema humile (MAYR,
1868), mit Ursprung im subtropischen Südamerika, ist in
vielen Teilen der Erde ein bedeutsamer Lästling. Um die
weltweite Verbreitung und das Potenzial für weitere Aus-
breitung zu bewerten, haben wir Nachweise von L. humile
von > 2100 Fundorten gesammelt. Da mehrere süd- und
mittelamerikanische Linepithema-Arten oft fälschlicher-
weise als L. humile bestimmt wurden, haben wir alle un-
bestätigten Nachweise aus Süd- und Mittelamerika ausge-
schlossen. Wir dokumentierten die frühesten bekannten
Nachweise von L. humile für 95 geographische Gebiete
(Länder, Inselgruppen, große Inseln und US-Bundesstaa-
ten), einschließlich einiger, für die wir keine bisher ver-
öffentlichten Nachweise gefunden haben. Für einige süd-
und mittelamerikanische Länder konnten wir keinen der
veröffentlichten Berichte von Vorkommen von L. humile
Die meisten Nachweise von L. humile stammen aus den
Subtropen, insbesondere aus Regionen mit mediterranem
Klima (warm-trockene Sommer und kühl-feuchte Winter),
einschließlich dem ursprüngliche Verbreitungsgebiet in Süd-
amerika und exotische Populationen in Kalifornien, dem
Mittelmeerbereich, dem südlichen Afrika, sowie in Aus-
tralien, Neuseeland und Japan. In humideren subtropischen
Gebieten, wie dem Südosten der Vereinigten Staaten, domi-
niert L. humile nur selten außerhalb urbaner Bereiche. In
tropischen Gebieten dominiert L. humile nur in Höhenla-
gen, mit Hawaii als prominentem Beispiel. In temperaten
Gebieten ist L. humile fast ausschließlich ein Lästling in
Linepithema humile hat bereits die meisten subtropi-
schen Gebiete mit Tieflage und mediterranem Klima er-
reicht, ist aber bisher für die meisten tropischen Gebiete mit
Höhenlage und geeignetem Klima nicht nachgewiesen. In
der Vergangenheit hat L. humile tropische Regionen wahr-
scheinlich am Seeweg in Folge menschlicher Handelsak-
tivitäten erreicht und musste die Tieflandbedingungen der
Küste überleben, um sich anschließend in kühlere Höhen-
lagen ausbreiten zu können. Heute ermöglicht die Luftfahrt
L. humile, als blinde Passagiere in Frachtgut an nahezu jeden
Punkt der Erde zu gelangen. Deshalb ist eine fortschreiten-
de Ausbreitung des Lästlings für die Zukunft zu erwarten.
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    We examined the impact of the non-indigenous Argentine ant, Linepithema humile (Mayr), on the native ants of Santa Cruz Island (SCI), the largest of the California Channel Islands. Linepithema humile, a South American native, was first found on SCI in 1996 and now occupies two areas comprising less than 1% of the island. We surveyed ants using four methods: visual surveys, bait stations, tree surveys, and soil/litter samples. We found a total of 23 ant species, including two species not native to SCI: Cardiocondyla ectopia Snelling and Linepithema humile. Numerous native ants occurred at sites uninfested by L. humile and co-occurred with L. humile at the outer boundaries of L. humile-infested territory, but at sites more than 10m within L. humile-infested territory, all but two of these species disappeared, probably due to exclusion by L. humile. Only two tiny ant species, Solenopsis molesta Say and Monomorium ergatogyna Wheeler, were found to coexist deep within the L. humile-occupied areas.
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    The Argentine ant, Linepithema humile, is an invasive species with the potential to cause significant economic and ecological damage in New Zealand. Using published information on rates of development, we induced parameters for a cumulative degree-day model for each life-stage of the Argentine ant.A summary model suggested that complete development, from egg to worker, requires approximately 445 degree-days above a threshold of 15.9°C. Meteorological records of air and soil temperatures indicated a number of sites in New Zealand that fulfil this minimum temperature requirement on an annual basis. Maps based on soil temperature data indicated suitable conditions as far south as Central Otago, while air temperature data predicted a more limited northerly distribution in Northland and Hawkes Bay. Additional factors, such as microclimatic variation, thermoregulatory behaviour, biotic interactions and dispersal opportunities will also be important in determining the precise range limits of the Argentine ant in New Zealand.
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    The isolated Mid-Atlantic Ridge islands of Ascension Island (8° S), St Helena (16° S), and Tristan da Cunha (37° S) are 1700 - 2800 km from Africa, the nearest continent. We compiled published, unpublished, and new records of ants from these islands and evaluated the probable origin of each species. We examined specimens representing 20 different ant species: ten from Ascension, 16 from St Helena, and one from Tristan da Cunha. These included three new records from Ascension (Pheidole teneriffana FOREL, 1893, Solenopsis sp. 1, Strumigenys emmae (EMERY, 1890)), five new records from St Helena (Hypoponera sp. 1, Linepithema humile (MAYR, 1868), Monomorium latinode MAYR, 1872, Monomorium cf. sechellense, Pheidole teneriffana), and the first identifica- tion of the only ant species known from Tristan da Cunha (Hypoponera eduardi (FOREL, 1894)). All confirmed island records, except Camponotus fabricator (F. SMITH, 1858) and Hypoponera punctatissima (ROGER, 1859) on St Helena, included specimens from 1995 or later. We could not confirm two additional published ant species records from As- cension (Cataglyphis sp., Tapinoma sp.) and one from St Helena (Camponotus castaneus (LATREILLE, 1802)). Most, if not all, of the 20 ant species we documented on South Atlantic islands, including C. fabricator, a putative St Helena endemic, may be exotic species that arrived accompanying humans. However, it is possible that some ants were present before human arrival. One candidate for native status is Cardiocondyla mauritanica FOREL, 1890, a widespread tramp species originally from Africa, found on Ascension in many uninhabited areas.