Volunteer Jo Fern describes her experience looking for Argentine ants on Great Mercury Island.

Date:  23 March 2017

Volunteer Jo Fern on Great Mercury Island.
Volunteer Jo Fern on Great Mercury Island

I want to tell you about my exciting week ant hunting!

Hunting for Argentine ants.
Hunting for Argentine ants

It appears that not all ants are created equal. I was given an amazing opportunity to spend a week with DOC staff and pest eradication experts on Great Mercury Island hunting Argentine ants. Possums, rats, mice all get a lot of pres, but I have to say before now I didn’t know anything about Argentine ants. From what I have learnt this week they could be the next big threat to our native wildlife.

The ants arrived into NZ in 1990 from Melbourne, Australia on building materials bought in for the construction of Mount Smart Stadium. Since then they have spread throughout much of the North and South Islands. The ants are very aggressive and are highly invasive. In fact they are classed as one of the world’s top 10 most invasive species.

Unlike other ant species Argentine ant colonies are able to cooperate and communicate and form huge super colonies. They are highly territorial and will attack other native ant species. They not only compete for food with other native invertebrates, lizards and birds but they also eat other native invertebrates and lizards and also bird eggs.

The ants were discovered on Great Mercury Island in 2013. Since the eradication of rats, cats and mice was achieved in 2014, the main aims of this trip were to establish how far Argentine ants had spread throughout the island, and for trip co-ordinator Peter Corson, to conduct a feasibility study to ascertain whether eradication of the ants is also achievable.

The essential tool when hunting Argentine ants is a large stick. They inhabit mostly warm, dry, elevated sites, usually under rocks or cow patties. By banging your stick around the edges of a potential nest site the aggressive ants swarm out in large numbers and at a very fast rate. To determine if they are Argentine ants you then place your hand near them. Most native ants will avoid your hand and run for cover but the 'argies' will swarm all over your hand biting you. They are a small ant, only 2–3 mm in length and they are a honey brown colour – most other ants are quite dark black. Often a good indicator of a nearby nest is a large trail of ants, often 4 or 5 wide (most other ant species will only be a single ant trail). They will often take the path of least resistance, in other words they will run along wires, pipes, walls, branches rather than negotiating long grass. Once a nest had been found we logged its position on a GPS locater and used a specialised ant toxin applied directly onto them to wipe out the colony.

For those of you who haven’t had the opportunity to visit Great Mercury it is a truly spectacular Island. The effort, dedication and financial commitment of the owners and DOC to eradicate mammalian pests is starting to pay dividend as native birds species return and reptile and insect numbers increase. However, if the Argentine ant population is left to multiply unchecked, it risks jeopardising all their hard work. The long term ecological restoration goal for the island involves being able to release endangered bird, reptile and insect species back onto the island, but until the 'argies' are under control this just isn’t viable.

Those who live on the island are working hard to reduce the spread of the ants, but allowing public access means there is always a risk of argentine ants and other pests being re-introduced by visitors. It’s a continuous challenge but ultimately it should hopefully be a rewarding one.

I hope to be given the opportunity to do a follow up study in another 6 weeks to see just how effective the treatment has been and to really get to grips with how feasible eradication of these invasive pests is.

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