African big-headed ants are a major threat to native ecosystems and have been successfully eradicated from several regions including Kakadu National Park, a campsite in the Daly River region, the Tiwi Islands and isolated places throughout north-east Arnhem Land. There is also an eradication program on Lord Howe Island, now in its final stages.

The Challenge

African big headed ants are a major pest

African big-headed ants (Pheidole megacephala) are listed as one of the 100 worst pests in the world.

African big-headed ant

The ants are a major threat to biodiversity and the environment because they can readily out-compete and displace native invertebrates, even to the point of local extinction.

Rainforest ecosystems are most at risk.  For example, in the Howard Springs Nature Park in the Northern Territory, African big-headed ants have completely displaced all native ant species and reduced the populations of other invertebrates by up to 80 per cent.

The major (soldier) workers have huge heads, contributing almost half of the body size. The minor workers, which are seen more often, are small (about 2 mm) and vary in colour from light to dark brown.

African big-headed ants are slow moving, do not bite or sting, and have no smell when crushed.

Our Response

Working together

Since the early 2000s CSIRO has been working in collaboration with land managers, particularly Aboriginal Ranger groups, across northern Australia to eradicate African big headed ant from remote locations.

The Results

Successful eradications

In the early 2000s, CSIRO and Kakadu National Park staff eradiated African Big-headed ants from a 30 hectare site within the World Heritage listed site.

Following on from the success in Kakadu, CSIRO worked with the MalakMalak Rangers from the Daly River region south of Darwin to eradicate a significant population.

Further work with the Dhimurru Rangers has resulted in three populations of African big-headed ants being eradicated from north-east Arnhem Land, while the Tiwi Land Rangers have eradicated the ant from Tiwi Islands north of Darwin.

In 2012 CSIRO was engaged by the Lord Howe Island Board to provide expertise and oversight for the African big-headed ant eradication program on Lord Howe Island. To date, all known infestations of the ant have been treated, and most locations have already been declared free of the ant. The last known surviving ants were recently detected on a single property in March 2016, and the infested area has been re-treated. If no more ants are found in the next two years, the ant will be declared eradicated from Lord Howe Island in March 2018.

Listen to the podcast with Dr Ben Hoffman, speaking about the African Big-headed ant eradication program on Lord Howe Island.

Pests in paradise: saving Lord Howe Island from the ants

Glen Paul: G'day and welcome to CSIROpod, I'm Glen Paul.

Since developing long distance transportation humans have been responsible for intentionally and unintentionally introducing invasive species across the globe. In the case of the African big headed ant it was small enough to stow away on a ship or aircraft. As its name suggests it's native to Africa but has now spread to nearly all temperate and tropical parts of the world. Because of its impact on biodiversity it's firmly placed in the 100 worst invasive alien species list. Lord Howe Island, approximately 570 kilometres to the east of Port Macquarie, is a World Heritage area and regarded as one of the most beautiful islands in the Pacific. Since 1993 it's been subject to invasion by African big headed ants. Joining me on line to discuss measures the Lord Howe Island Board and CSIRO have been taking to turn this situation around is CSIRO ecologist Dr Ben Hoffman.

Ben, for an invasive species to make the 100 worst list it's obviously got to be pretty bad. Why is this ant such a problem?

Dr Hoffman: This ant has a full suite of impacts environmentally, socially and economically. In the environment it's able to out compete and kill off many of the species that it co-exists with, particularly invertebrates and other ants. Socially, it's a very big nuisance within houses and a problem for electrical appliances and so economically it's a big issue with us trying to deal with it in social situations as well as agriculturally because it harbours the likes of bugs which reduce crop productivity and can also spread crop diseases.

Glen Paul: OK, so it definitely deserves its spot in that list. As the name suggests, it has a big head. Is that true of all categories and how does their appearance differ from other ants?

Dr Hoffman: Yes, this ant has two size classes – minor workers and major workers. It's only the major worker that has a disproportionately large head which is approximately half the size of the body. It's not unique to the species, there are approximately 500, maybe even 600, native big headed ant species and big headed ants are found all around the world but this one particular species just seems to be far more successful than most, hence it's become a major invasive species globally.

Glen Paul: I guess its colour is the reason why, in some parts of Australia, it's referred to as the Coastal Brown ant.

Dr Hoffman: It has many names. For some reason it got the name Coastal Brown Ant, maybe because it's very common throughout the east coast. Personally I don't use it because any ant that thrives in Alice Springs is not coastal.

Glen Paul: True. What about their colonies? Do they have Queen Ants? How quickly do they multiply?

Dr Hoffman: Yeah, in a normal ant species we would have one or just a few Queens per nest. Individual nests or colonies of a species would compete against each other. This ant is unique, and unique among just a few highly successful invasive ant species, where there is no limit to the number of Queens they can have per nest or per colony and individual nests and colonies don't fight with each other. They basically act as one cooperative unit that can cover vast areas, even hundreds of hectares, and create what's called a Super Colony.

Glen Paul: Is that also through Queens being able to fly in the nuptial stage like other ants and spread further afield?

Dr Hoffman: Another unique feature of this ant is that the Queens typically don't fly, even though they do possess wings and are capable of flight. Typically they don't go and start their own nests, they go and join an existing colony and therefore increase the number of Queens and the reproductive output of that colony. The spread of this ant is usually very slow, it's literally at walking pace of the ant and they'll normally only spread tens of metres per year as opposed to kilometres which can be done by flight.

Glen Paul: What impacts are they having on Lord Howe Island?

Dr Hoffman: On Lord Howe Island we haven't directly measured the impacts of the ants, we don't really need to. We know that it's such an invasive species that we don't even really want to waste time trying to work out if it's a threat over there or what it would be a threat to, we simply want to get rid of it. For that reason we've gone straight into the eradication program.

Glen Paul: What does that entail?

Dr Hoffman: Eradication of this ant is actually quite easy; I think it's the easiest ant in the world to eradicate. There are products on the market that this ant is very susceptible to and susceptible with just a single treatment. For that reason it's one of the ants that has the highest number of eradications around the world. All we do is we go into an area, we map its distribution which is simply a case of finding where the ant is and finding where the limits of its distribution are and then we apply an ant bait that is broadcast throughout that whole area. You'll find that typically the ants are eradicated after that one treatment. The only times when we do have persistent populations is usually just within buildings and we now know that we need to treat the inside of the buildings as well, not just externally. Within a matter of months we can map an infestation, treat it and then the ant is gone and we monitor it for the next two years to ensure that the ant is completely gone.

Glen Paul: How do you monitor for that with them being so small and able to conceal themselves?

Dr Hoffman: There's no easy way of monitoring for an ant and proving that it's gone, it's a really hard slog and a laborious task. The best way is to put out some food, something like cat food – ants love anything that has fish involved in it – and literally putting out thousands of spoonful's of cat food throughout an area, spaced every few metres apart and then coming back within half an hour to an hour later and seeing what ants are there and its simply presence or absence of this ant species.

Glen Paul: What would be the worst case scenario if left unchecked in a sensitive environment such as Lord Howe Island?

Dr Hoffman: Look, we know exactly what this ant is capable of if left unchecked. A good example is on Hawaii where many invasive ant species have now spread to where ants weren't native, all the native plants and animals weren't used to ants and many of them have gone extinct because of the invasive ant species. We're talking invertebrates even through to lizards, notable reductions in bird reproduction… all of these cases would occur on Lord Howe Island.

Glen Paul: I understand that they can also add to the destructive power of other species, lending them a helping hand.

Dr Hoffman: Yes, this ant has gone to these very small islands on the Capricornia Cays on the Great Barrier Reef that harbour a particular tree called Pisonia Grandis which is a rare tree, only found on coral atolls, but a very important tree for the breeding of seabirds and for some reason this ant population has also got over there in the presence of an introduced scale population and together the population of the two species increases to a point where the scales literally suck the life out of the trees and the entire tree population collapses and you end up with basically a deserted island with no habitat for the ants and this is an extreme case of what the ant is basically capable of doing. Most unique for Lord Howe Island is that they've recently rediscovered a stick insect that was thought to be instinct which is the Lord Howe Island phasmid and its now only present in captive populations but they would like to re-release it into the wild and this ant is one of the two factors that need to be removed so that the phasmids can be released into the wild, the other factor being rats and so a rat eradication is also about to commence soon. Basically, if the ant is present in the environment this phasmid will be knocked out almost immediately.

Glen Paul: So once its eradicated how do you then stop it turning up on the next flight into Lord Howe Island or perhaps via the port?

Dr Hoffman: Yes, keeping a species out of any location is just as applicable for Lord Howe Island as it is for anywhere else and for any eradication project. One of the first things we've done is to improve the biosecurity of Lord Howe Island, particularly by increasing awareness of invasive ants and their identification and now all of the goods coming onto the island are inspected, there's a lot more compliance and awareness of what needs to be done to keep things from coming out to Lord Howe Island and also the port facility on the island is now routinely monitored and also treated for ants, just in case something manages to sneak on.

Glen Paul: It sounds like you're winning the battle to keep beautiful Lord Howe Island beautiful. Thanks very much for discussing it with us today, Ben.

Dr Hoffman: No problems, thank you.

Glen Paul: Dr Ben Hoffman. And to find out more about the research or to follow us on other social media just visit us on www.csiro.au

Pests in paradise: saving Lord Howe Island from the ants :  CSIRO and the Lord Howe Island Board are winning the battle to save the world heritage area from the invasive African Big-headed ant, which is capable of forming enormous colonies and wiping out many native creatures.

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