Why Are Argentine Ants Successful Invaders?

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Argentine ants (Linepithema humile) are dark brown ants from South America that have found their way to various countries, including countries in North America. Argentine ants are known to be successful invaders. This alien species has displaced the native species of ants and other flora and fauna of the places it has invaded.

So why are Argentine ants successful invaders? Linepithema humile has done successful invasions on the areas they've been introduced to, rooted in the fact that they're introduced populations of ants that have no natural enemies. The fact that they can have multiple queens and form supercolonies are key traits that they have used to change their environment to their benefit.

Learn More: Why Are Argentine Ants Bad?

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Why Are Argentine Ants Considered As Invasive Species? 

Invasive species are animals or plants that have been brought by human activity to other parts of the world that they're not previously found in. In this new environment, these populations successfully displace the native populations of animals or plants because of the absence of predators or other natural enemies.

Linepithema humile ants fit this definition of invasive organisms. L. humile are an ant species from South America, believed to have been brought from Brazil to the United States in the 1890s aboard coffee ships. Since then, they have aggressively dominated the native populations of ants in the United States.

Linepithema humile can form supercolonies with a high genetic similarity that they're considered a megacolony of interconnected networks. They cause changes in their environment that are detrimental to the native flora and fauna and to human activities. For example, they can protect aphids and other plant pests due to the sweet substances that these organisms can produce, while killing off plant pollinators.

Factors That Dictate The Invasion Success Of Argentine Ants

The ecological success of L. humile in the new environment they've encountered lies in their social organization, in that they can produce new queens and can have multiple queens. This is the reason why Argentine ant colonies thrive even upon the death of their previous queen. This is in contrast to other ant species in which they have a permanent queen in which its death leads to the death of their colony. 

Other factors that dictate the invasion success of Argentine ants include the following:

1) Less Genetic Variation Than Native Ants

Linepithema humile is a type of social insect organized in a way that protects its queen from setting foot in its nest. The queen needs not set out to mate and can do so safely inside its nest. Moreover, a single colony of L. humile can bud off from its parent supercolony and establish its own supercolony due to the ability of the L. humile to produce multiple queens. 

What sets L. humile apart from other social insects is the fact that they have low genetic differentiation. They do so by choosing and killing multiple queens a year, especially those that can alter their genes. This high genetic similarity within their group is important so as to keep the harmony between the L. humile colonies, in that they have the ability to borrow each other's worker ants should they deem it needed.

Through this high genetic similarity, aggression between nests is also avoided, making their numbers easy to grow. Although note that this isn't a foolproof method as there are reports of an L. humile supercolony is attempting to break off from its parent supercolony, resulting in the death of millions of ants per year.

2) Larger Propagule Linked To Increased Aggressiveness

The large L. humile propagule size, coupled with their aggressive behavioral traits, leads to the displacement of native ant species. A good example of this is the Californian carpenter ants (Camponotus spp.) that are considerably larger in size than L. humile but they're outnumbered by L. humile, causing their defeat and even leading to L. humile using their displaced colonies as a food source.

This was tested in a study by Sagata & Lester (2009). They manipulated the L. humile propagule size in the laboratory and in the field, observing the interaction of L. humile with each other and with the native ant species, Monomorium antarcticum.

In this study, they were able to demonstrate that a smaller L. humile propagule size leads to them avoiding conflicts. Larger propagules are significantly more aggressive than smaller propagules, with them successfully annihilating the native ant colonies and even the smaller propagules.

3) Use Of Chemical Weapons

Despite the lack of acidopore, L. humile ants are also still capable of releasing chemical irritants to combat their enemies, even larger ones at that. The L. humile ants are capable of releasing chemicals through a behavioral trait called "gaster bending", in which they point their gaster towards their opponent's body and release an irritating substance made up of dolichodial and iridomyrmecin.

Upon releasing the substance from their gasters, L. humile ants then seize this opportunity to defeat their opponents as the substance is capable of incapacitating their opponent. They then recruit more ants toward the target and together, groups of ants pull apart the limbs of their opponents and ultimately kill them.

Scientists were able to recreate this substance and they envision it to have a wide range of applications in pest control. They see it as a possible bait for L. humile ants towards poisons and a possible agent to repel native ant species.

4) Response To The Environment

The invasion success of L. humile ants may be controlled by biotic (living) and abiotic (non-living) factors. It was demonstrated in the study that L. humile ants need an environment that must be suitable for them to thrive, otherwise they're incapable of living in that environment, much less invading it.

Linepithema humile ants are largely dependent on soil moisture, in that they can't occupy dry environments. However, it was shown that their invasion isn't dependent on precipitation, unlike native species. Their invasion is more dependent on winter, in that they're more successful in inhabiting areas with lesser winter temperatures.

Native ant species also can slow down the invasion of L. humile ants but can't prevent them in certain areas such as wet environments because of the difference in the response of L. humile ants and native ants to these environments. Through these invasions, increased fragmentation of native ant species is observed, leading to an increase in extinction risk of these native ant species.

L. humile ants are also said to be widely spread through human activities, making humans the primary mediators of their spread to new environments. 

Read More: How To Tell If Your Ants Are Argentine Ants

5) Possible Relationship Between Diet Breadth And Invasion Success

The invasion success of an L. humile colony is indicated by the width of their distribution ranges. Meanwhile, it was already established that in general, a wide diet breadth (meaning, being more adjustable to food) is linked to a more successful biological invasion of a species.

Taking these into consideration, a study investigated the reason why an L. humile colony may be more successful than others in invading a new territory despite the high genetic similarities of these populations. In this study, they were able to observe and infer that more successful biological invasions of L. humile are indeed linked to a wider range of food composition compared to other less successful L. humile supercolonies. 

Signs Of Argentine Ant Infestation

The most telltale sign of Argentine ant invasions is a trail consisting of uniform-looking brown L. humile worker ants. This trail is usually 3 ants wide and directed towards sources of food and moisture, such as kitchen counters and leaky water pipes. When you attempt to disturb their trail and block them using your hands, they readily climb your fingers, a behavioral trait not typical with other ant species.

The identification of L. humile against other native and invasive ant species is also an important aspect of looking for signs of Argentine ant infestation. For instance, crushing this ant species leads to the production of a musty odor unlike the rotten coconut odor released by odorous house ants (Tapinoma sessile). Another differentiating biological trait of this species is the absence of sting and acidopore (an orifice where ant venom is released), unlike other ant species like red imported fire ants (Solenopsis invicta).

Impact Of Argentine Ant Infestation 

L. humile are considerably small compared to other ant species and they don't have stings or venoms that can make their bites painful to humans. However, due to the aggressiveness of L. humile colonies, the consequences of ant invasions are grave, with a wide range of impacts from the biodiversity of the native populations to the social and economic aspects of human activities. 

1) Biodiversity Impacts

Linepithema humile ants are capable of biological invasions of native populations, outcompeting even the largest species just by their sizes alone. They can also attack and eat the chicks of birds and drive their mothers away.

Being insects that prefer sweet food, L. humile ants turn to flowers as a food source. They can overtake honeybees and sap-sucking insects to these flowers, causing a decline in the population of these insects. This in turn affects the pollination and reproduction of flowers, especially because L. humile ants are poor pollinators.

2) Social Impacts

Argentine ant invasion causes a significant disturbance in the lives of people and our activities. There are many reports of people selling their homes if they're infested with L. humile, especially because they can't move around the house normally and let their children play for fear of them getting bitten by the ants. L. humile ants also swarm towards the water and food source, being visibly annoying in the eyes of those living within the house they've infested with.

3) Economic Impacts

Losses in certain industries, most notably the agricultural industry, occur because of the Argentine ant invasion. In an attempt to control these species, pest treatment efforts lead to higher costs of production. They can also create holes in water pipes of orchards, with it also causing significant losses in production.

Moreover, L. humile ants rob honey from bees and can even kill and eat bees. A similar thing occurs in poultry farms in which chicks are attacked by ants and the mothers die due to stress. They can also decrease the quality of food by contaminating it. 

Control And Prevention Of Argentine Ants 

Control and prevention of L. humile infestation may be done via physical or chemical means. 

For physical means, you can always seal the entry points of these pests so they can't have access to your homes. Potted plants must also be inspected before placing them anywhere inside the house for they can harbor L. humile. Regularly check your pipes for leaks and always clean your house so they can't be enticed to enter.

For chemical means, you may use insect sprays that are specially formulated to kill pests such as L. humile. You can also use slow-acting baits that can entice the ants into collecting them but kill these ants afterward. However, these chemicals may also pose harm to your kids and your pets. Alternatively, you can also use safer products such as eucalyptus oil as natural insect repellents.

If it gets too bad that it can't be handled with these procedures, you can always contact professional pest control services such as Pinnacle Pest Control, as we're equipped with the right technology and experience in pest control and management.

Learn More: Do Argentine Ants Bite?

Combat Even The Most Successful Invaders With Pinnacle Pest Control

pest control worker doing ant control with pesticide spray

Linepithema humile ants are domestic pests that have posed significant impacts on the lives of people and the population of native species. They're successful invaders that are difficult to eradicate because of their key traits such as the ability to make many queens but having interconnected networks of L. humile supercolony. 

With Pinnacle Pest Control, no pest is too difficult to exterminate because of our team of experts in pest control. We also use the best and latest technology in combating even the most successful invaders such as L. humile. Contact us today at 916.381.5793 to get a free quote and inspection.

Guaranteed Pest Extermination Services, Right at Your Doorstep

No matter what kind of pest problem you’re dealing with, you can count on Pinnacle Pest Control to provide top-notch pest extermination services. With decades of experience under our name, we have already helped hundreds of residents and business owners in Sacramento eliminate pests in their property and keep them away for good.

Call Now

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