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

Abstract

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.

Full text

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
Abstract
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: wetterer@fau.edu
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: alexwild@illinois.edu; avsuarez@life.uiuc.edu
Dr. Núria Roura-Pascual, Centre for Invasion Biology, Department of Botany & Zoology, Stellenbosch University, Pri-
vate Bag X1, Matieland 7602, South Africa. E-mail: nrourapascual@gmail.com
Prof. Dr. Xavier Espadaler, 2. Ecology Unit, Universidad Autónoma de Barcelona, E-08193 Bellaterra, Spain. E-mail:
xavierespadaler@gmail.com
Introduction
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.
Methods
We documented the range of L. humile using both published
and unpublished records. Antbase.org 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
such.
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
188

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.
Results
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).
Discussion
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-
video
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
189

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):
≤ Palermo
+ 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.):
≤ Hammamet
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.
190

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):
≤ Douglas
+ 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):
≤ Swakopmund
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
191

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).
Acknowledgements
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-
port.
Zusammenfassung
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
bestätigen.
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
Gebäuden.
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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