Why Invasive Ants Are a Silent Threat to Our Ecosystems

<span classe="légende">The yellow crazy ant (Anoplolepis gracilipes) is a notorious invasive ant species.</span> <span class="attribution"><a classe="lien " href="https://www.shutterstock.com/image-photo/fourmi-folle-jaune-anoplolepis-gracilipes-1960533274" rel="pas de suivi pas d'ouverture" cible="_vide" données-ylk="slk:Lukman_M/Shutterstock;elm:lien_contexte;itc:0;sec:canvas-contenu">Lukman_M/Shutterstock</a></span>” src=”https://s.yimg.com/ny/api/res/1.2/paQIyp9RqPqtE3F3WrQ.rw–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTcxNA–/https://media.zenfs.com/en/the_conversation_464/946f07b1fc948aea5f70580796585df2″ data-src=”https://s.yimg.com/ny/api/res/1.2/paQIyp9RqPqtE3F3WrQ.rw–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTcxNA–/https://media.zenfs.com/en/the_conversation_464/946f07b1fc948aea5f70580796585df2″/></div>
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<p>Invertebrates are often described by experts as the “little things that run the world,” and ants are certainly a leading contender for this role. Ants help ecosystems function normally, and the combined weight of all the ants on Earth is roughly equivalent to 1.4 billion people, or 33 Empire State Buildings.</p>
<p>Unfortunately, some ants have become invasive species, which are organisms that are transported to a new ecosystem and cause damage. These introductions usually happen by accident, but can have disastrous consequences, as my team’s new research shows.</p>
<p>Invasive species are considered the second greatest threat to biodiversity after habitat destruction. They are a leading cause of animal extinction, potentially leading to species extinction and ecosystem failure.</p>
<p>The International Union for Conservation of Nature (IUCN) has listed five ant species among the world’s 100 most dangerous invasive alien species. But while invasive ants have dramatically transformed some of the areas they have invaded, others appear to be much less affected, or even completely unaffected.</p>
<h2>How dangerous are invasive ants, really?</h2>
<p>My team’s study draws on research from around the world to provide a measure of the negative or positive impact of invasive ants on biodiversity loss. The results show us that invasive ants are just as bad as we thought.</p>
<p>We extracted data from 46 different research papers that studied how animal communities responded to invasive ants, and combined the results. We only selected research conducted in relatively “undisturbed” natural environments, free of intensive human activity.</p>
<p>These are areas where invasive ants have dispersed from more degraded habitats or urban environments. This allows us to say with greater certainty that any negative or positive effects on animal communities are due to invasive ants, rather than other invasive species or some form of human disturbance such as agriculture or deforestation.</p>
<p>Our results show that animal communities respond extremely negatively to invasive ants. We found that there were on average 50% fewer animals and species in areas invaded by ants, which represents a dramatic drop in biodiversity. It is also important to remember that these results are averages, and therefore invasive ants can mean the end of some animal communities beyond these numbers.</p>
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Close-up of an ant with a large head crawling along a piece of mossy bark.

We also found that some types of animals, such as birds, reptiles and beetles, reacted more strongly than others. Native ants were the group most strongly affected.

This makes sense, because many native ants will not only be directly attacked by invasive ants, but they will also have to compete with them for food and nesting sites. It is also bad news because of the overall importance of native ants to the broader ecosystem.

Other groups seriously affected were birds, beetles, butterflies, moths and reptiles.

We also found that the number of individuals of one group of insects – insects like scale insects, aphids and mealybugs – increased. This group forms “mutualisms” with ants, where each species has a net benefit.

These insects suck the sap and secrete a sweet liquid called “honeydew,” which ants love. In exchange for this sweet secretion, the ants defend these insects from predators and parasites, allowing their populations to mutually increase. In some cases, these mutualisms can facilitate invasion—and have disastrous consequences.

How can something so small cause such a big problem?

Although ants are small compared to humans’ perception of the world, they are numerous and tend to interact with a wide range of other organisms. This means that they can influence the ecosystem from multiple angles of attack. Invasive ants probably actively prey on other species, but competition for food or space is also important.

Ultimately, we need more research to understand how ants interact with other species when they invade a place. What do they eat? Who do they compete with for food? What habitats do they prefer and why? These questions urgently need to be answered so that we can understand, prioritize, and optimize how to minimize the negative impacts of invasive ants.

Read more: Why red fire ants and yellow crazy ants gave each other the green light to invade Australia

Overall, our research is worrying. Reductions in animal diversity can have serious consequences for ecosystem functioning and the long-term future of rare species. While there are critical considerations for mitigating or reversing these effects, the conservation implications are not clear.

Ant eradication programs are logistically complex and financially costly, and more than half of them fail. Early detection technologies, along with control measures such as toxic baits, can help conservationists prevent or reverse the effects of invasive ants on our ecosystems.

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Maximillian Tercel receives funding from the Natural Environment Research Council and the Durrell Wildlife Conservation Trust.