What are the problems invasive ants cause?

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)

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)

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

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.

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

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!

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)

The Argentine ant (Linepithema humile) displaces almost all other ant species where it occurs. This can have serious consequences for other members of the ecological 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 

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 ecological community.

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

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)

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.

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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)

These sap sucking insects directly damage the plants and spread plant diseases.

The ants protect the sap sucking pests from predators, which allows the pests to increase their numbers. In return the ants collect the sugary honeydew that the sap suckers excrete.

The ants also make it difficult for stock animals such as pigs and chickens to eat or sleep and the ants may also kill and eat newly hatched chicks.

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A difficult white-footed ant "farming" a sap-sucking pest (© Alex Wild)

Red imported fire ant biting and stinging (© Alex Wild)

Fire ant stings are extremely painful (© State of New South Wales through NSW Department of Industry)