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Argentine Ants: the unassuming pest in Aotearoa

Updated: May 29, 2020

Argentine ants are quietly taking over the world - but what are they? How can we control them? And what can you do to help?



Worldwide, we've seen many examples of the consequences of the spread of humans. In Aotearoa, we constantly see issues with animals purposefully introduced, generally for some type of financial gain, such as possums for the fur trade. However, there are also many examples of species that have been accidentally introduced through global human dispersion, some of which we still know very little about. This is the case for public enemy number one: Argentine ants.



What are Argentine Ants?

The Argentine ant (Linepithema humile) is a highly invasive, honey coloured ant native to Argentina, Brazil, and Paraguay. Their spread throughout the globe initially went unnoticed, because they cannot sting or bite human skin and therefore did not pose a physical threat. However, they can be distinguished from common ants due to the following characteristics:

  • Small size (2—3 mm)

  • Substantial populations

  • Rapid, single file movements

The diet of Argentine ants in Aotearoa is highly opportunistic, resulting in direct competition with many native species such as nectar-eaters, lizards, other invertebrates, and insectivores like kiwi. They have been observed to consume animals up to the size of an entire native bird egg. However, as well as predating native species, they also destroy ecosystems by inhibiting the decomposition process.


Argentine ants are often found in homes and close to humans and consequently have been distributed widely through human commerce; thus, they are known as a tramp species. Global conservation organisations consider the Argentine ant one of the top 100 most invasive alien species in the world, due to their ability to form extremely large colonies and destroy entire ecosystems. Additionally, they form extremely large colonies, which is a huge contributing factor toward their invasivity.



Can we control them?

Argentine ants certainly have many traits that make them extremely difficult to control, hence their global distribution. The main behaviours include:


Budding – when worker ants sense disturbances, they ‘bud off’ by picking up larvae and eggs and quickly moving to a new location. These disturbances can include climatic changes, literal human disturbance, or the detection of poisonous substances such as bait.

Super colonies – Argentine ants form cooperative super-colonies meaning extensive numbers of ants working together. Baiting one small portion of an infested area does little to control population. This increases extermination costs and hence, volunteers are needed to help reduce their populations.


However, thankfully, there are traits that can help us control their populations and spread, so long as we are smart about our movements:


Bait can work

Baiting is usually performed by laying down non-poisonous bait to identify the extent of the Argentine Ant colony. Their super-colonies overwhelm ecosystems to the stage that no other invertebrate species are able to successfully stay established. This means that once a perimeter is established, poisonous bait can be laid down with little impact to native species.


Dispersal

These ants actually spread very slowly without human assistance, only advancing up to 150 m per year. This means that so long as we can be very careful with not spreading them ourselves, we have a chance at controlling them.


Anything is possible!

Through extensive labour, the ants have been successfully removed from one location – Tiritiri Matangi. Tiritiri Matangi is a 220 ha island, eradicating Argentine ants took 16 years; however, it demonstrates that if enough people work together, we can elicit real change.



How can you help?

The war will be nasty and long, but there are organisations worldwide that are on the front lines. In Aotearoa, if you would like to volunteer, you can help eradicate Argentine ants on Great Mercury Island, or check local community volunteering forums for new opportunities. Alternatively, you can fight from your own backyard. Here are some ways that you could help:


  • Be a proactive gardener: check soil before planting in your garden. If you are buying new plants, do the same before taking them to your house. An easy way to determine if they are Argentine ants is by placing your hand on their nest. If they swarm erratically over your hand, they are likely Argentine ants; if they are placid then they are likely regular ants. Alternatively, if you’re not keen on receiving one thousand ant hugs, if you see small, erratic, honey coloured ants in the store, let staff know.

  • Be a proactive camper: going for a hike/family camping trip? Check your gear! Especially if you are travelling to a place with endangered species. Make sure any food is in sealed containers and that all zips are completely done up. Avoid placing bags directly onto the ground whilst travelling to your destination.

  • Kill the beasts: hardware stores and garden stores such as Bunnings or Kings Plant Barn sell products that will kill ants. We recommend first using non-poisonous baits, such as a sugar water solution, and putting this into small open containers. This will attract ants and help determine which areas need to be poison baited and which areas need to be avoided to protect areas occupied by native species.


Ward D. F., & Toft, R. (2011). Argentine ants in New Zealand. Retrieved March 25, 2020, from http://argentineants.landcareresearch.co.nz/


Daugherty, M. (n.d.). Argentine Ant. Retrieved March 25, 2020, from https://cisr.ucr.edu/invasive-species/argentine-ant


Department of Conservation (n.d.). Argentine Ants. Retrieved March 25, 2020, from https://www.doc.govt.nz/nature/pests-and-threats/animal-pests/argentine-ants/


Stanley, M. C., & Ward, D. F. (2012). Impacts of Argentine ants on invertebrate communities with below-ground consequences. Biodiversity and Conservation, 21, 2653–2669. Retrieved from https://doi.org/10.1007/s10531-012-0324-0


Veitch, C. R., Clout, M. N., Martin, A. R., Russell, J. C., & West, C. J. (2019). Effort required to confirm eradication of an Argentine ant invasion: Tiritiri Matangi Island, New Zealand. Retrieved March 29, 2020, from http://www.issg.org/pdf/publications/2019_Island_Invasives/Green.pdf


Holway, D. A. (1995). Distribution of the Argentine Ant (Linepithema humile) in Northern California. Conservation Biology, 9(6)1634—1637. Retrieved from www.jstor.org/stable/2387207


Lowe, S., Browne, M., Boudjelas, S., & De Poorter, M. (2000). 100 of the world's worst invasive alien species. Retrieved March 28, 2020, from www.issg.org


Suarez, A., V., Holway, D. A, & Case, T. J. (2001). Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from Argentine ants. Proceedings of the National academy of Sciences of the United States, 98(3), 1095—1100. Retrieved from https://doi.org/10.1073/pnas.98.3.1095


Danielle is a student at Auckland University of Technology studying a double major in Environmental Science and Applied Conservation. She is a keen hiker that tries to identify every plant along the way. She has been known to make up the names of birds or trees if someone asks and she doesn’t know.


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