Environmental stresses (such as those caused by human practices, such as monoculture) may cause explosions of some ant populations, an effect that is particularly evident within ants’ native ranges. For example, in its native range in South America, the little fire ant Wasmannia auropunctata is a pest in disturbed forests and agricultural areas where it can reach high densities. High densities of W. auropunctata have been linked with sugar cane monocultures and cocoa farms in Colombia and Brazil, respectively. In Colombia, a high abundance of the little fire ant in forest fragments has been linked with low ant diversity. The little fire ant efficiently exploits resources including nectar, refuges within vegetation and honeydew residues (of Homopteran insects), and it may out-compete and displace native myrmecofauna (Armbrecht and Ulloa-Chacón 2003). Improved land management and a reduction of primary production will alleviate the problems associated with invasive ants and the environmental stresses that cause ant population explosions.
In agricultural areas, due to the close association of the land and workers, the little fire ant may be a great nuisance to humans. This is because it is more likely to reach high densities and sting people working in the field. The increased numbers of Homoptera insects, which sap plant nutrients and make plants susceptible to disease, may cause substantial yield losses. In Cameroon, on the other hand, the spread of the little fire ant is encouraged, due to the fact that it preys on, and thereby has a role in the control of, certain herbivorous cocoa pests (Bruneau de Mire 1969, in Brooks and Nickerson 2000).
W. auropunctata may have negative impacts on invertebrates and vertebrates. They may prey on native insects and cause declines in the numbers of small vertebrates. In human habitations it may sting, and even blind, domestic pets (cats and dogs) (Romanski 2001). It is believed to have caused a decrease in reptile populations in New Caledonia and in the Galapagos Archipelago, where it eats tortoise hatchlings and attacks the eyes and cloacae of the adult tortoises (Holway et al. 2002; J. K. Wetterer pers. comm., 2003). The little fire ant is probably the most aggressive species that has been introduced into the Galapagos archipelago, where a marked reduction of scorpions, spiders and native ant species in infested areas has been observed (Lubin 1984, Clark et al. 1982, in Roque-Albelo and Causton 1999). Similarly it has been noted to decrease local arthropod biodiversity in the Solomon Islands (Romanski 2001).
W. auropunctata rarely buries myrmecochorous seeds and sometimes ingests elaisomes without dispersing seed. In its native range, the little fire ant decreases herbivorous arthropod biodiversity, increasing the fruit and seed production and growth of the plant and decreasing pathogen attacks. W. auropunctata may also, however, exclude arthropod plant mutualists, such as plant tenders or seed dispersers (Ness and Bronstein 2004).
Please read Invasive ants impacts for a summary of the general impacts of invasive ants, such as their affect on mutualistic relations, the competitive pressure they impose on native ants and the effect they may have on vulnerable ecosystems.
Location Specific Impacts:
Human nuisance: Several residents in the infested area were stung by ants whilst swimming in their swimming pools. Dogs and cats have been stung by the ants. People working in their gardens have also been stung by the ants.
Competition: High populations of W. auropunctata have been related to marked reductions of other ant species in agricultural lands such as cocoa farms in Brazil (Delabie 1988, Majer et al 1994, in Armbrecht and Ulloa-Chacón 2003).
Cauca River Valley (Colombia)
Competition: W. auropunctata is widely distributed throughout South America and is able to displace the local myrmecofauna. The positive relation between W. auropunctata abundance and ant-plant associations in understory vegetation reinforces the belief that W. auropunctata is highly able to exploit and monopolise resources such as extrafloral nectar, refuges within vegetation, and honeydew residues from Homopteran insects, and prevent other ant species from utilising these resources successfully (Armbrecht and Ulloa-Chacón 2003).
Economic/Livelihoods: Colonises disturbed and agricultural areas, sometimes becoming an economic problem (Fowler et al. 1990, in Armbrecht and Ulloa-Chacón 2003).
Galapagos Islands (Ecuador)
Interaction with other invasive species: "Wasmannia auropunctata is often associated with another serious pest: the cottonycushion scale- Icerya purchasi, and has been observed transportingimmature stages and tending colonies" (Wetterer & Porter, 2003).
Reduction in native biodiversity: The little fire ant is probably the most aggressive species that has been introduced into the Galapagos Archipelago. Marked reductions in scorpions, spiders, and native ant populations in areas infested with the little fire ant have been observed. Many other arthropods are probably also affected, but this has not been measured (Roque-Albelo and Causton 1999).
Human nuisance: Images and text by Eric Loeve available at Fenua Animalia document the enormous impact of this invasive ant on people's lives. This is a sign of things to come as the Wasmannia auropunctata infestations become more and more established and as the scale and numbers build.
Reduction in native biodiversity: A progressive blindness syndrome known as as “Florida spots”, “Florida keratitis/keratopathy” or “tropical keratopathy” (Roze et al, 2004; Moore, 2005) has been documented in mammals and other animals that live in the proximity of colonies of the little fire ant. No scienific study had been conducted to prove that the little fire ants were responsible for this.
Scientists from Fenua animalia conducting mapping of a little fire ant colony in the Mahina commune’s highs (Tahiti), discovered that ant colony areas were also sheltering endemic hearths of "Florida keratopathy". 24 cases of keratopathy and 12 control cases were studied within the mega-colony settled. Results of an analysis showed that the affected animals were those living in contact with the ants. Apart from this predisposing factor, the scientists did not find any other characteristic facilitating this outbreak (age, sex, viral status regarding Feline leukosis). The study highlights the symptoms of acute attack such as blepharospasm and whimpering; and the topography of injuries shows that the median area of the eye is the most affected. Though the pathopysiologic model is not already understood, the authors of the study, believe as many authors previously cited that the most probable etiologic agent of this pathology is the littel fire ant Wasmannia auropunctata (Dr. Leonard Theron Assistant - Faculty of Veterinary Medicine of Liege- Production Animals Clinical Department pers.comm., September 2009).
Other: "Wetterer et al. (1999) found anecdotal evidence of an impact onvertebrates in Gabon. House cats (Felis catus) at Lopé often have W.auropunctata in their fur, and several cats developed corneal cloudingand blindness. William Karesh, field veterinarian for Wildlife Conserva-tion Society, found the cats' symptoms consistent with trauma, not communicable disease. More disturbingly, elephants (Loxodonta africana) with cloudy corneas arecommon in Lopé and Petit Loango, as well as Wonga Wongué Reserveon the central coast of Gabon (100 km south of Libreville). The possibleconnection between W. auropunctata and eye maladies deserves furtherstudy."
Reduction in native biodiversity: W. auropunctata has a negative impact on the native ant community in Gabon. Nine sites In Lope National Park were surveyed. A highly significant correlation between ant diversity and length of infestation by W. auropunctata was found. Many more native ant species were present in areas not infested with W. auropunctata (39.0 ± 4.6) compared with areas infested by W. auropunctata for approximately 5–10 yr (7.0 ± 6.2 and 1.7 ± 1.2, respectively). In infested areas, W. auropunctata made up the bulk of specimens collected in every plot (Walker, 2006).
New Caledonia (Nouvelle Calédonie)
Human nuisance: Causes painful stings.
Reduction in native biodiversity: W. auropunctata have a negative impact on endemic ants, native arachnids, beetles, and reptiles (Wetterer & Porter, 2003 and references therein).
Wewak (Papua New Guinea)
Human nuisance: The ants over-run gardens and homes in residents' houses and sting people, especially children. Control of insect pests within houses is expensive and many families may be forced to live with the ant.
Guadalcanal (Solomon Islands)
Human nuisance: Causes painful stings.
Other: Locals on Guadalcanal have reported that their dogs (Canis domesticus) were all gradually blinded by the ants' venom andrarely lived more than five years (Wetterer 1997 in Wetterer & Porter, 2003).
Hawaii (United States (USA))
Economic/Livelihoods: Many important economic crops in Hawaii are harvested by hand. W. auropunctata is small, cryptic, and has a painful sting. In some cases, agricultural workers refuse to harvest from infested trees or orchards, which is a critical issue for farms that rely on hand harvesting. W. auropunctata is also of quarantine concern, because the presence of ants on exported fruits and vegetables from Hawaii can cause rejection and return shipment to Hawaii (Costa et al., 2005; Follett & Taniguchi 2007 in Souza et al., 2006)
Human nuisance: Cause painful stings.
Economic/Livelihoods: It deters people from tending their crops, reducing productivity and imposing economic hardship on them.
Human nuisance: It stings people and animals including chickens and can cause allergic reactions in people
Vanua Lava Is. (Vanuatu)
Reduction in native biodiversity: A striking lack of butterflies has been noted on the island of Vanua Lava. This is compared to Mota Lava, which is free of W. Auropunctata and has abundant butterflies (J. Tennant, pers. comm. in Wetterer & Porter, 2003).