What are the problems invasive ants cause?

Invasive ants can have devastating effects on people's lives, agriculture and the environment. The following stories are just a few of many stories that describe the impact these ants can have.

Little fire ants cause problems all over the PacificYellow crazy ants make life a miseryInvasive ants destroy propertyTiny ants cause massive problemsInvasive ants harm vulnerable wildlifeEcological relationships are disruptedInvasive ants can destroy entire ecosystems!

Little fire ants cause problems all over the Pacific

Little fire ants (Wasmannia auropunctata) cause extreme hardship for people living and farming in invaded areas. The ants tend sap-sucking insects, which stress crops and encourage plant diseases, reducing yields for farmers. Harvesting is also difficult due to the ant’s painful sting.

In New Caledonia, the Galápagos Islands and French Polynesia, farms, such as coffee and citrus plantations where the crops must be harvested by hand, have been completely abandoned to the little fire ant. It is extremely painful for farmers to gather the pods or fruits due to the stinging ants, and some plantations find it unprofitable to pay workers the increased wages they would require to work under such conditions.

Moeana Besa's story

In French Polynesia, Moeana Besa's life and her family’s have been completely transformed for the worse by little fire ants. They once got everything they needed from the land; she grew their food, as well as flowers to sell in town. Her extended family lived close by. In this video she describes her land before little fire ants as a paradise.

Invasion of little fire ants has changed all that.

Now the family’s crops of taro and pineapple are infested and inedible, many fruit trees and coconuts have died and she has to buy all their food. She can no longer grow flowers to sell, so instead makes and sells fabric flowers. Her children are not allowed to play in the yard. Her relatives that used to live nearby have all abandoned their land. Even wild animals, such as pigs, have disappeared from the infested area.

 

Little fire ants not only sting, but support sap-sucking insects which encourage plant diseases like the fungus shown here growing on coffee (© Cas Vanderwoude)

Moena Besa's land has been taken over by little fire ants (© MISC)

A reaction to little fire ant stings in Papua New Guinea (© Cas Vanderwoude)
 

Little fire ant stings in Papua New Guinea (© Cas Vanderwoude)

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Yellow crazy ants make life a misery

Little fire ants aren't the only invasive ant that can make everyday life difficult. Where the yellow crazy ant (Anoplolepis gracilipes) reaches incredibly high abundances they can make life a misery.

When there was a population explosion of yellow crazy ants in Tokelau, people had ants crawling over them day and night. Ants infested their homes and were constantly in their food as they tried to eat.

Frank Tedo, who lives beside the World Heritage Wet Tropics in Queensland, Australia, was temporarily blinded after these acid-spraying ants overran his sugarcane farm. This pest has also devastated his sugarcane crop.

Frank Tedo talks about living in a yellow crazy ant infested zone, YouTube video (© Invasive Species Council, Australia)
 

The damage yellow crazy ants do to sugarcane, YouTube video (© Invasive Species Council, Australia)

Yellow crazy ants are not the only ants that cause blindness. Little fire ants are known to blind livestock and pets, though wild animals are affected as well.

   

 These domestic animals have been blinded by little fire ants (© Cas Vanderwoude)

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Invasive ants destroy property

In the Tiwi Islands, Australia, the African big-headed ant (Pheidole megacephala) and Singapore ant (Trichomyrmex destructor, formerly Monomorium destructor) cause over 100 000 AUD in electrical damage every year.

These ant species seem to be attracted to electrical current and enter electrical equipment, where they chew through wires, destroying equipment and sometimes causing fires.

Another invasive ant that is strongly attracted to electrical devices is the tawny crazy ant (Nylanderia fulva), not yet in the Pacific. This ant is estimated to cause over 146.5 million USD in electrical damage to the southern United States every single year! Most of that is paid by homeowners who must repair or replace shorted out appliances and vehicles. These ants also cause electrical fires in people's homes and businesses making them a serious hazard.

 

Tawny crazy ants forced these people to abandon their home, YouTube video (© Animal Planet)

A farmer from Alabama talks about having red imported fire ants infesting his farm, YouTube video (© Invasive Species Council, Australia)

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Tiny ants cause massive problems

A red imported fire ant simultaneously biting and stinging a person (© Alex Wild)
 

 The damage invasive ants can cause should not be underestimated due to their small size. The red imported fire ant (Solenopsis invicta) has been estimated to cost the United States 5.65 billion USD a year! These costs include management, damage to infrastructure, impacts on agriculture and medical costs.

More than 5 million people are stung every year in the United States, and since their introduction, over 80 people have died as a result of red imported fire ant stings (usually due to an allergic reaction).

Aside from their painful sting and devastating impact on wildlife, red imported fire ants also damage crops and fruit trees. The farmer from Alabama in the above video lost 200 citrus trees in one year!

These ants not only eat seeds, they also eat roots, shoots and fruits of many food plants. In China rice paddies have been abandoned due to infestations of red imported fire ants.

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Invasive ants harm vulnerable wildlife

In Hawaii, seabird colonies are under attack by yellow crazy ants. Ground nesting seabirds, such as red-tailed tropicbirds and wedge-tailed shearwaters, return to the same site to nest every year. In colonies that have been invaded by yellow crazy ants these birds suffer terribly as the acid-spraying ants are constantly running over them. Often their eyes swell shut due to the acid and they have to try to take off blind.

Red-tailed tropic birds have been observed crashing into bushes while trying to take flight blind due to the acid from the ants. Many of the birds had given up trying to breed on Johnston, but because these birds will only nest in the same spot every year, this means that they were not simply breeding elsewhere.

Seabird chicks are also suffering. Chicks growing up in infested areas are hard hit by the constant acid-spraying of the ants. They develop abnormalities as they grow - missing toes, misshapen beaks, shrunken eyeballs. Sometimes the damage is so severe that their nostrils close up

and skin grows over their eyes. Chick survival is greatly reduced in invaded areas compared with neighbouring uninvaded areas.

 
Red tailed tropicbird being swarmed by yellow crazy ants (© Stefan Kropidlowski / USFWS)
Yellow crazy ants are attacking seabirds in Hawaii, YouTube video (© GeoBeat News)
A healthy shearwater chick is covered in downy feathers (© Sheldon Plentovich / USFWS)
 
A chick that was attacked by yellow crazy ants has lost its downy feathers, is blind and has a deformed beak (© Sheldon Plentovich / USFWS)

African big-headed ants (Pheidole megacephala) harm seabirds as well. Ants cover a bonin petrel on Kure Atoll, Hawaii (© Sheldon Plentovich)
 

African big-headed ants on a bonin petrel chick. The webbing on the feet are particularly vulnerable to attack. A lot of this chick's feet has been eaten (© Cynthia Vanderlip)

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Ecological relationships are disrupted

As well as directly attacking wildlife, invasive ants may additionally indirectly impact them by killing off other species they rely on for food or interrupting mutualisms they need to survive.

The Argentine ant (Linepithema humile) displaces almost all other ant species where it occurs. This can have serious consequences for other members of the community. For example, coastal horned lizards depend on large native ant species for food.

When Argentine ants wipe out these native ants, the lizards can starve to death. Most of the lizards don’t seem to see Argentine ants as suitable prey, and when they do, eating the tiny Argentine ants doesn’t provide enough nutrition for baby lizards to grow or maintain their weight.

 

A coastal horned lizard (© Bureau of Land Management Oregon and Washington, CC BY 2.0, via Wikimedia Commons 

In South Africa the Argentine ant has disrupted a mutualism between a plant and it's seed disperser.

Many plants in the South African fynbos (native shrubland) rely on ants to disperse their seeds. These ants collect the seeds and bury them, which protects them from predators and fire (which is common in the fynbos).

Argentine ants interfere with this relationship by eliminating the other ant species but failing to disperse the plant seeds themselves, leaving them vulnerable to predators and fire. Invasion by Argentine ants has been shown to completely change the composition of plant communities in this habitat, having unknown, but potentially serious effects on other members of the community.

 

Fynbos (native shrubland) in South Africa (S. Molteno, Wikipedia)

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Invasive ants can destroy entire ecosystems!

This is happening on Christmas Island in the Indian Ocean.

Yellow crazy ants tending yellow lac scale insects (© Pete Green)
 

Red land crabs are abundant in areas not invaded by yellow crazy ants (© Monica Gruber)

Some time in the early 1990’s the yellow crazy ant population on Christmas Island exploded and soon yellow crazy ant supercolonies covered 25% of the island's rainforest on the island. This population explosion coincided with the arrival of a scale insect from southern Asia, which produces lots of honeydew. These scale insects provide the yellow crazy ants with a steady source of carbohydrate resources allowing them to achieve huge worker abundances.

The yellow crazy ant also benefits the yellow lac scale insect by protecting it from predators in return for honeydew. Abundances of scales can be so great they completely coat tree branches. 

One of the yellow lac's favourite host trees is the Tahitian chestnut (Inocarpus fagifer), a tree highly valued in the Pacific for its food value, medicinal properties and cultural values. The high ant densities are very hard on the trees and can cause them to die.

The yellow crazy ant population explosion has been a disaster for the rainforest ecosystem on Christmas Island. Yellow crazy ants prey on the native red land crab, and completely eliminate them. Between the late 1990s and early 2000s it’s estimated that these ants killed between 10-15 million land crabs, or between a quarter and a third of the total population.

As red land crabs are the dominant consumer on the forest floor, the ant is also indirectly changing forest structure on the island. Usually the red land crabs keep the forest floor clear by eating most new seedlings. Without them, the forest becomes very dense, and more introduced tree species survive and thrive. The absence of the crab and increased leaf litter has also helped another invader, the giant African land snail, which has increased 250-fold in yellow crazy ant invaded areas.

Additionally, the large numbers of understory plants shades out the canopy seedlings. This means there are few new canopy trees to replace old ones that fall or are killed by the scale insect. As some birds and other animals depend on these canopy trees for food and shelter their numbers decline. This in turn affects the birds and other animals that preyed on them. All of these factors results in massive changes to the entire ecosystem.

 
A site without yellow crazy ants (© Pete Green)
A site infested with yellow crazy ants. Without the red land crabs the vegetation grows unchecked (© Pete Green)
Red land crabs cannot survive in areas with yellow crazy ants (© Director of National Parks Australia)

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Information sources

Abbott. 2005. Supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on an oceanic island: forager activity patterns, density and biomass. Insectes Sociaux 52: 266-273

Abbott, Green. 2007. Collapse of an ant-scale mutualism in a rainforest on Christmas Island. Oikos 116: 1238-1246

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Bond, Slingby. 1984. Collapse of an ant-plant mutualism: the Argentine ant (Iridomyrmex humilis) and myrmecochorous Proteaceae. Ecology 65(4): 1031-1037

Christian. 2001. Consequences of a biological invasion reveal the importance of mutualism for plant communities. Nature 413: 635-639

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Department of Agriculture. 2006. Prevention and Control of Red Fire Ant in China. Report by the Chinese Department of Agriculture

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Lard, Schmidt, Morris, Estes, Ryan, Bergquist. 2006. An economic impact of imported fire ants in the United States of America. Department of Agricultural Economics, Texas A&M University

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Maui Invasive Species Council, Little fire ants are bad news for food crops

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Natural Resources Defense Council (NRDC), https://www.nrdc.org/onearth/christmas-crab-massacre

New York Times Magazine, http://www.nytimes.com/2013/12/08/magazine/crazy-ants.html?_r=0

Northern Land Manager, http://www.landmanager.org.au/exotic-ants-threaten-indigenous-land

O’Dowd, Green, Lake. 2003. Invasional 'meltdown' on an oceanic island. Ecology Letters 6: 812-817

Pacific Biosecurity. 2016. Socio-economic costs of invasive ants. Report to Landcare Research, NZ

Pacific Islands Fish and Wildlife Office, https://www.fws.gov/pacificislands/articles.cfm?id=%20149489561

Plentovich, Russell, Camacho. 2012 The effects of yellow crazy ant (Anoplolepis gracilipes) invasion and subsequent control on burrow-nesting seabirds in the Hawaiian archipelago. 20th Annual Hawai’i Conservation Conference (Talk) https://vimeo.com/56951284

Scientific American, http://www.scientificamerican.com/article/the-rise-of-the-crazy-ants/

Strohecker. 2012. Moeana’s message - what Tahiti can teach us about little fire ants. Kia’i i Nā Moku o Maui Nui, Spring 2012

Suarez, Case. 2002. Bottom-up effects on persistence of a specialist predator: ant invasions and horned lizards. Ecological Applications 12(1): 291-298

Suarez, Richmond, Case. 2000. Prey selection in horned lizards following the invasion of Argentine ants in Southern California. Ecological Applications 10(3): 711-725

Theron. 2005. The Wasmannia auropunctata linked keratopathy hypothesis: the Polynesian case. Veterinary Medicine Master Paper, Universit

USFWS Pacific Region, http://usfwspacific.tumblr.com/post/67589291621/saving-seabirds-from-an-island-invasion

Vanderwoude. 2008. Operational plan for management of Wasmannia auropunctata (little fire ant) in East Sepik Province, Papua New Guinea. VCL New Zealand

William, Whelan. 1992. Bait attraction of the introduced pest ant, Wasmannia auropunctata (Hymenoptera: Formicidae) in the Galapagos Islands. Journal of Entomological Science 27(1): 29-34