How to know if we’re winning the war on Australia’s fire ant invasion, and what to do if we aren’t


Fire ants like these can give a nasty bite.
Shutterstock/SweetCrisis

Daniel Spring, University of Melbourne and Jonathan Keith, Monash University

More than A$400 million of government funding is being invested in the latest round of the fire ant program in the hope of eradicating the invasive pests by 2027.

But recent reports on the ABC suggest the invasion is spreading beyond containment lines in south-east Queensland, and there are delays in responding to public reports of new ant infestations.

The claims are denied by Graeme Dudgeon, the new general manager of Queensland Government’s National Red Imported Fire Ant Eradication Program.




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Fire ants are native to South America but nests were first discovered in Brisbane in 2001. It’s thought they arrived via shipping at the Port of Brisbane.

They’re regarded as one of the world’s worst invasive species and have a painful bite which is why the Queensland Government has been trying to wipe them out here.

Is eradication possible?

An independent review in 2016 found the fire ants were confined to a region of south east Queensland and said there was an opportunity to eradicate the pests.

But the latest debate raises the question of whether eradication is the best plan, or would further containing the spread of the fire ants be a more practicable solution?

To achieve its aim of eradicating the fire ant problem, the program needs to progressively shrink the invasion.

If the invasion is shrinking too slowly (or is expanding), eradication won’t be achieved by 2027. Without ongoing monitoring of the invasion’s size, the program might be failing without the general public knowing.

But knowing the fire ant invasion’s size isn’t easy because there isn’t enough funding to survey all locations that might have them.

Estimates of the invasion

Using records of past fire ant detections, we have demonstrated how to estimate the invasion’s size when only part of the managed area is surveyed.

Our inference of the boundary of the fire ant invasion in April 2015. The different coloured polygons correspond to different levels of credibility that the boundary contains the invasion, with the outermost boundary corresponding to the highest credibility. Small crosses represent sites where nests have been detected, with the most recent detections in red and the oldest in brown.
Nature/Authors provided, CC BY

If this approach to estimating the invasion boundary is applied each year during the current program, we could estimate whether the invasion is shrinking fast enough to be gone by 2027.

The importance of this issue demands a rigorous scientific analysis using transparent data and methods. Without this, anecdotal evidence that the current invasion is spreading is all we have to indicate whether eradication efforts are failing.

The size of the fire ant invasion should not only be measured in terms of the total area within its estimated boundary but also the density of nests within this area.

Eradication won’t be achieved if both the invasion boundary and the density within it are increasing. This straightforward test to determine whether the program is failing has not yet been applied.

But such a test could be done if updated records of the fire ant invasion are regularly made available to allow for periodic estimation of updated maps of the invasion.

Never give up

Even if eradication by 2027 is unlikely, this does not mean we should give up, provided future control efforts can contain the invasion at an affordable cost.

If the current program fails to eradicate the fire ants, it may still set the stage for effective long-term containment of the invasion.

A poor outcome will result if current management efforts are spread thinly over the infested area, reducing the density of nests but not eradicating them from any suburbs.

A better outcome would involve shrinking the infested area, that is, eradicating the ants from many or most suburbs, so that subsequent containment efforts can focus resources on a smaller area.

Is it still early enough in Australia to shrink the fire ant invasion to a manageably small area and thereby protect most homes and most of the environment for a long time? The required information to answer this question is not yet available.




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But if Queensland’s eradication program has substantially slowed the spread so far, this provides confidence that continuing the program could effectively suppress the invasion. If so, we need to estimate what it will cost to keep out fire ants from most homes and most of the environment for a long time.

It’s often claimed that removing the last 1% of invaders costs as much as removing the previous 99%. If the current program removes all ants from most areas by 2027, this may provide large benefits without the extra cost of finding the last few ants in all infested areas.

Even if we do eradicate fire ants this time, it’s almost certain they will be back because they can readily hitchhike rides on ships.

So if governments can keep fire ant numbers down through ongoing containment, a lot of people and a lot of native species will benefit.The Conversation

Daniel Spring, Research Fellow, School of Biosciences, University of Melbourne and Jonathan Keith, Associate Professor, School of Mathematical Sciences, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Invasive ants: federal budget takes aim but will it be a lethal shot?



File 20190404 131415 1ag8r2w.jpg?ixlib=rb 1.1
Argentine ants are a fact of life in many parts of Australia, but can still potentially be banished from Norfolk Island.
Davefoc/Wikimedia Commons, CC BY-SA

Lori Lach, James Cook University

Amid all the usual items we expect to see in the federal budget was one that raised eyebrows: A$28.8 million for three ant eradication programs.

Yet amid the inevitable media puns about the government “upping the ant-e”, we should note that these funds are for the continuation of existing programs that have already attracted significant funding and made substantial progress. Stopping now would have meant previous funding was wasted.

The funds will go a long way towards protecting Australia’s economy and environment from the damage wrought by invasive ants. But despite the apparent cash splurge, it nevertheless falls short of what is really needed.

Of the $28.8 million, $18.3 million was for the National Red Imported Fire Ant Eradication Program. These funds are part of a $411 million, ten-year program begun in 2017 to eradicate red imported fire ants from southeast Queensland, the only place they are found in Australia.




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Removing these pests will avoid an estimated $1.65 billion in total costs to 19 different parts of the economy. With previous funding, the program eradicated these ants from 8,300 hectares near the Port of Brisbane, making it the world’s largest ant eradication to date.

The Yellow Crazy Ant Eradication Program was allocated $9.2 million over three years. Yellow crazy ants have caused a cascade of ecological effects on Christmas Island, and at their peak abundance temporarily blinded a Queensland cane farmer with their acid spray.

The Wet Tropics Management Authority, which runs the program, had requested $6 million per year for six years to continue removing the ant from in and around the Wet Tropics World Heritage Area. The federal funding is $3 million short of this, and the authority is still waiting to hear whether the Queensland government will provide the remainder.

Since 2013, the program has received $9.5 million from the federal government (and $3 million from the Queensland government). No yellow crazy ants have been observed in about half of the target area in more than a year. A yet-to-be published analysis estimates the benefit-cost ratio for the program as 178:1.

“It’s a mop-up operation… we’ve got our foot on the throat of this thing.”

A further $1.3 million was allocated to the Argentine Ant Eradication Strategy on Norfolk Island in the South Pacific. Argentine ants have invaded places with Mediterranean-type climates all over the world, including southwestern Western Australia and parts of southern Australia, and become firmly established. But unlike those areas, the population on Norfolk Island is still considered small enough to be eradicable, and federally funded efforts to remove them began in 2010.

Yellow crazy ants in Queensland and Argentine ants on Norfolk Island directly threaten World Heritage Areas. The ants can have significant impacts on native birds, mammals, insects, reptiles, amphibians, and plants. Getting rid of them is important for meeting Australia’s international obligations to protect World Heritage sites.

What is ant eradication?

Ant eradication means removing all individuals of a particular ant species from a given area.

The first step is to define the extent of that area. Depending on the species, this may involve visual searches and/or placing lures such as sausages, cat food, or jam to attract the ants. The public can help by notifying relevant authorities of unusual ants in their gardens, and by not transporting materials that have ants on them.

The second step is treatment. Currently, the only way to eradicate ants is with insecticidal baits. Ants’ social structure makes this particularly challenging: killing the queens is vital for eradication, but queens typically stay sheltered in the nest – the only ants we see out foraging are workers.

Some of the most problematic ant species can have hundreds of queens and tens of thousands of workers per nest. They can reach extraordinarily high densities, partly because invasive ant species, unlike most of our native ant species, do not fight one another for territories.

Yellow crazy ants, proving it is possible to feel sorry for a cockroach.
Bradley Rentz/Wikimedia Commons, CC BY-SA

Beating ants means turning their biology against them. Bait needs to be attractive enough for workers to bring back to the colony and share, but not so deadly that they die before they get there. (And yes, this means if you’re spraying foraging ants in your kitchen you won’t get rid them for good, because the queens are somewhere hidden, laying more eggs and making more ants.)

Most ant eradication programs take three to four years to fine-tune their baiting regime because of a multitude of factors that need to be considered, such as seasonal changes in ant foraging behaviour and food preference, and the desire to avoid harming non-target species. Typically, two to six treatments are required, depending on the ant species, the size of the area, and the habitat type.

Beating the 1%

The hardest part of ant eradication is the end-game. Getting rid of the final 1% requires first finding them. This may mean painstaking searches through hundreds of hectares of bushland and residential areas, and the placement of hundreds of thousands of lures. Detector dogs can be very helpful, but they cannot be used in all environments and also need substantial resources for training, handling, and maintenance.

Ironically, it is at this stage that public and political support for eradication programs is most likely to wane, because ant numbers are too low to be seen as a threat to the public, economy or environment. Yet it is vital not to stop now, or else the remaining 1% will simply build up their numbers again. Experienced staff are also lost when programs suffer cuts or delays in their funding.




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Disappointingly not mentioned in the budget was funding for eradicating electric ants. Like red imported fire ants, electric ants have a painful sting, and when left to multiply will eventually turn gardens and swimming pools into no-go zones. They also pose a significant threat to native animals such as the southern cassowary, and can blind animals as large as elephants.

They are currently only found in the Cairns region. The National Electric Ant Eradication Program, funded by federal and state governments, ran from 2006 until 2017 and had likely reduced numbers down to that last 1%. The program has been running on state funding with reduced staff since then, but several new detections in the past three months demonstrate the cost of the gap in funding.

In those inevitable “federal budget winners and losers” lists, invasive ants have found themselves firmly in the losers column for 2019. But it’s worth remembering that most of the world’s roughly 15,000 known ant species provide vital services for the functioning of our ecosystems.

They aerate soil and redistribute its nutrients, protect plants from herbivores, disperse seeds, and repurpose dead organisms. They may even help slow down the spread of those pesky invasive ants that are much less friendly.The Conversation

Lori Lach, Associate Professor, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Cannibalism helps fire ants invade new territory



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Fire ant stings can be deadly to people who have an allergic reaction to their venom.
Forest and Kim Starr/Flickr, CC BY-SA

Pauline Lenancker, James Cook University and Lori Lach, James Cook University

Tropical fire ants (Solenopsis geminata), originally from central and South America, are a highly aggressive, invasive ecological pest. Our new research has shed light on how they successfully establish new colonies.

An allergic reaction to painful tropical fire ant bites.
Pauline Lenancker, Author provided

While we don’t know exactly how widespread tropical fire ants are in Australia, they are well established around Darwin and Katherine, as well as on Christmas Island and Ashmore Reef. Disturbing one of their nests will result in many workers inflicting painful stings on the intruder, and can trigger an allergic reaction in some people.

When invasive ants move to a new region, the pioneers may be one or a few colonies. Because these pioneers are isolated, they often inbreed, which causes genetic problems in their offspring. But our new research, published in Scientific Reports, reveals how tropical fire ants use cannibalism to survive and spread, despite their low genetic diversity.




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Sons and daughters

Founding new colonies is how fire ants spread. Queens fly off to start their own colonies just after they have mated. It is a perilous journey – they need to avoid predators and find a good spot to start laying eggs. If queens do not quickly rear daughters that can forage, called workers, they will starve to death.

Queens can lay two different types of eggs: fertilised eggs, which will develop into workers, and unfertilised eggs, which will develop into males. Therefore, female workers have two copies of each gene (diploid), while males have a single copy of each gene (haploid). However, when an ant queen and her mate are closely related, a flaw in the sex determination system of ants causes half of the fertilised eggs to develop into diploid males instead of workers.

The role of males is only to mate with queens – they do not forage, and they die after they have mated. Queens founding a colony have no interest in producing males, because males will not feed them. What’s more, diploid males are often sterile, and their larvae are larger than worker larvae. Therefore, queens can waste precious resources feeding fat useless sons instead of workers.

We wanted to find out how common diploid males are in field colonies, and how queens could successfully start colonies despite them. Understanding how tropical fire ants spread, we hope, can help us stop them expanding their range.

Abandoned and eaten

Our field sampling of tropical fire ant colonies around Darwin revealed eight out of ten colonies produced diploid males.

We collected 1,187 queens that had just mated, and assigned them to start colonies on their own or with other queens.

We observed that in 34% of colonies producing diploid males, diploid male larvae were placed in the colony trash pile by the queens instead of being kept with the worker larvae. It is usual for ants to keep dead individuals away from the rest of the colony, but when we looked at some of these abandoned larvae under a microscope, we realised they were still alive.




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Queens not only abandoned their sterile sons, they ate them. Three-quarters of the 109 sterile male larvae disappeared from the colonies within 12 days of when we first observed them. Because the queens were the only adult ants present in the colony, this means the queens were eating their diploid males or feeding them to their worker larvae.

This cannibalistic behaviour allowed the queens to redirect nutrients towards themselves or productive members of their colony. Diploid male larvae require more food than worker larvae to develop, so we expected queens from diploid male producing colonies to lose more weight than queens from colonies that only produced workers, but we found that was not the case. Queens with diploid males lost less weight or as much weight as queens from regular colonies, probably because they ate their sterile sons.

We also found queens who worked together in groups to start a colony reared more workers. Therefore, queens in groups would likely have a better chance of survival even if they produced sterile males. But in 6% of colonies, queens did not tolerate having housemates and dismembered other queens.

A queen dismembered by a tetchy rival.
Pauline Lenancker, Author provided

For tropical fire ants, cannibalising sterile sons and cooperative brood rearing among queens are two behavioural mechanisms for avoiding inbreeding costs. A third possible mechanism for the queens is to “sleep around”.

Promiscuity would increase the chance of mating with a genetically different male, and reduce the likelihood of producing diploid sons.

Queens only mate right before starting their colony and store the sperm in an organ called the spermatheca. We genetically analysed sperm from the spermatheca of 40 queens, but found no evidence queens had mated with more than one male.

Tropical fire ants are currently established on Ashmore Reef, a protected Australian Marine Park which is an important breeding site for seabirds and turtles. The invasive ant threatens this sanctuary by attacking seabird and turtle hatchlings. Accidental spreading of tropical fire ants to suitable habitats in the Northern Territory, Queensland and Western Australia would threaten invaluable ecosystems as well as our health and lifestyles.




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The current eradication program for the closely related red imported fire ant (Solenopsis invicta) in Queensland has been granted A$411 million over ten years, and failure to eradicate red imported fire ants could cost Australia A$1.65 billion per year in damaged crops, livestock harmed and people treated. The more we learn about invasive ant biology, the closer we are to new methods of preventing their spread.The Conversation

Pauline Lenancker, PhD student in biology and ecology, James Cook University and Lori Lach, Associate Professor, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How we wiped out the invasive African big-headed ant from Lord Howe Island



File 20181106 74772 gz1lz8.png?ixlib=rb 1.1
Not welcome: the African big headed ant might be small but it can be a pest if it gets in your home.
CSIRO, Author provided

Ben Hoffman, CSIRO

The invasive African big-headed ant (Pheidole megacephala) was found on Lord Howe Island in 2003 following complaints from residents about large numbers of ants in buildings.

But we’ve managed to eradicate the ant completely from the island using a targeted mapping and baiting technique than can be used against other invasive species.

Up to 15% of Lord Howe Island was thought to be infested with the ant.
CSIRO, Author provided

A major pest

The African big-headed ant is one of the world’s worst invasive species because of its ability to displace some native plants and wildlife, and adversely affect agricultural production.




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It’s also a serious domestic nuisance. People can become overwhelmed by the large number of ants living in their buildings – you can’t leave a bit of food lying around, especially pet food, or it will be covered in ants.

It remains unclear how long the ant had been on Lord Howe Island, in the Tasman Sea about 770 km northeast of Sydney, before being found. But it is likely to have been present for at least a decade.

Because of the significant threat this ant posed to the conservation integrity of the island, an eradication program was started. But on-ground work done from 2003 to 2011 had many failings and was not working.

In 2011, I was brought in to oversee the program. The last ant colony was killed in 2016, but it is only now, two years later, that we are declaring Lord Howe Island free from the ants.

No African big-headed ants have been seen on the island for two years.
CSIRO, Author provided

A super colony

The ability to eradicate this ant is largely due to its relatively unique social organisation. The queens don’t fly to new locations to start new nests – instead, they form interconnected colonies that can extend over large areas.

This makes the ant’s distribution easy to map and treat. The ant requires human assistance for long-distance transport, so the ant will only be found in predictable locations where it can be accidentally transported by people.

From 2012 to 2015, all locations on the island where the ant was likely to be present were formally inspected. Priority was given to places where an infestation was previously recorded or considered likely. The populations were mapped, and then treated using a granular bait available at shops.

In the latter years we found 16 populations covering 30 hectares. Limited by poor mapping in the early years, we estimate that the ant originally covered up to 55 hectares, roughly 15% of the island.

Stopping the spread

The widespread distribution of the ant through the populated area of the island is thought to have been aided by the movement of infested mulch and other materials from the island’s Waste Management Facility.

To prevent any more spread of the ant, movement restrictions were imposed in 2003 on the collection of green waste, building materials and other high risk items from the facility.

The baiting program used a product that contains a very low dose of insecticide that has an extremely low toxicity to terrestrial vertebrates such as pet cats and dogs, birds, lizard etc. The toxicant rapidly breaks down into harmless chemicals after exposure to light.

No negative impacts were recorded on any of the native wildlife on the island.

Importantly, the African ant usually kills most other ants and other invertebrates where it is present, so there are few invertebrates present to be affected by the bait.

Ecological recovery of the infested areas was rapid following baiting and the eradication of the African ant.

Another ant invader

One of the main challenges was getting the ground crew to correctly identify the ant.

It turns out there was a second (un-named) big-headed ant species present, also not native to the island, that created a lot of unnecessary work being conducted where the African ant wasn’t present.

CSIRO and Lord Howe Island Board team tackling the African big headed ant problem.
CSIRO, Author provided

Like numerous other exotic ant species present, this second species was of no environmental or social concern, so there are no plans to manage or eradicate it.

The protocols used in this program are essentially the same that are being used in other eradication programs against Electric ant in Cairns and Browsing ant in Darwin and Perth, because those two species also create supercolonies.




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It is highly likely that those programs will also achieve eradication of their respective species, the first instance where an ant species has been eradicated entirely from Australia.

The fire ant program in Brisbane has many similarities, but there are distinct differences in that the ants there don’t form supercolonies that are so easy to map, and the area involved is far greater.The Conversation

Ben Hoffman, Principal research scientist, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Wasps, aphids and ants: the other honey makers



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Myrmecocystus honeypot ants, showing the repletes, their abdomens swollen to store honey, above ordinary workers.
Greg Hume via Wikimedia Commons, CC BY-SA

Manu Saunders, University of New England

There are seven species of Apis honey bee in the world, all of them native to Asia, Europe and Africa. Apis mellifera, the western honey bee, is the species recognised globally as “the honey bee”. But it’s not the only insect that makes honey.

Many other bee, ant and wasp species make and store honey. Many of these insects have been used as a natural sugar source for centuries by indigenous cultures around the world.




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By definition, honey is a sweet, sticky substance that insects make by collecting and processing flower nectar. The commercial association between honey and honey bees has mostly developed alongside the long-term relationship between humans and domesticated honey bees.

This association is also supported by the Codex Alimentarius, the international food standards established by the United Nations and the World Health Organisation. The Honey Codex mentions only “honey bees” and states that honey sold as such should not have any food additives or other ingredients added.

Oh honey, honey

Biologically, there are other insect sources of honey. Stingless bees (Meliponini) are a group of about 500 bee species that are excellent honey producers and are also managed as efficient crop pollinators in some regions. Stingless bees are mostly found in tropical and subtropical regions of Australia, Africa, Southeast Asia and the Americas.




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Their honey is different in taste and consistency to honey bee honey. It has a higher water content, so it’s a lot runnier and tastes quite tangy. Stingless bee honey is an important food and income source for many traditional communities around the world.

Harvesting “sugarbag”, as it’s known in Australia, is an important cultural tradition for indigenous communities in northern and eastern regions.

A sugarbag bee.
James Niland/Flickr, CC BY

Stingless bee honey production hasn’t reached the commercial success of honey bee honey, mostly because stingless bee colonies produce a lot less honey than an Apis honey bee hive and are more complicated to harvest. But keeping stingless bees in their native range for honey, pollination services and human well-being is an increasing trend.

Bumblebees also make honey, albeit on a very small scale. The nectar they store in wax honey pots is mostly for the queen’s consumption, to maintain her energy during reproduction. Because very few bumblebee colonies establish permanently, they don’t need to store large quantities of honey. This makes it almost impossible to manage these bees for honey production.

Bees aren’t the only hymenopterans that make honey. Some species of paper wasps, particularly the Mexican honey wasps (Brachygastra spp.), also store excess nectar in their cardboard nests. Local indigenous communities value these wasps as a source of food, income and traditional medicine.

Mexican honey wasp.
Wikimedia Commons

Ants have similar lifestyles to their bee and wasp cousins and are common nectar foragers. Some species also make honey.

“Honeypot ant” is a common name for the many species of ant with workers that store honey in their abdomen. These individuals, called repletes, can swell their abdomens many times the normal size with the nectar they gorge. They act as food reservoirs for their colony, but are also harvested by humans, particularly by indigenous communities in arid regions.

Close-up of three large replete honeypot ants (Myrmecocystus mimicus) at Oakland Zoo.
via Wikimedia Commons

These ants don’t just collect nectar from flowers, but also sap leaks on plant stems (called extrafloral nectaries) and honeydew produced by hemipteran sap-suckers like aphids and scale insects.

Aphids and scale insects aren’t all bad – they produce a delicious sugary syrup called honeydew. We mostly know these insects as garden and crop pests: warty lumps huddled on plant stems, often coated in sticky honeydew and the black sooty mould that thrives on the sugar.

Males of these insect species are usually short-lived, but females can live for months, sucking plant sap and releasing sweet sticky honeydew as waste from their rears. The sugar composition varies greatly depending on both the plant and the sap-sucking species.

Honeydew has long been a valuable sugar source for indigenous cultures in many parts of the world where native honey-producing bees are scarce. Many other animals that seek out floral nectar, like bees, flies, butterflies, moths and ants, also feed on honeydew. It’s an especially valuable resource over winter or when floral resources are scarce, and not just for other insects; geckoes, honeyeaters, other small birds, possums and gliders are all known to feed on honeydew.

Honeydew on a leaf.
Dmitri Don/Wikipedia, CC BY-SA

It’s also an indirect source of honey bee honey: plant sap that has been recycled through two different insect species! Honey bees are well-known honeydew collectors. In some parts of Europe, honeydew is an important forage resource for bee colonies.

Honeydew honeys have a unique flavour, depending on the host tree the scale insects were feeding on. Famous examples of this specialty honey are the German Black Forest honey and New Zealand’s Honeydew honey.




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So why not find out a bit more about what insects are producing honey in your local region?The Conversation

Manu Saunders, Research fellow, University of New England

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Nature’s traffic engineers have come up with many simple but effective solutions



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Ant colonies direct traffic flows of millions of individuals along the best routes – army ants even manage inbound and outbound lanes – but how?
Geoff Gallice/Wikimedia, CC BY

Tanya Latty, University of Sydney

This is the third article in our series, Moving the Masses, about managing the flow of crowds of individuals, be they drivers or pedestrians, shoppers or commuters, birds or ants.


As more and more people move to cities, the experience of being stuck in impenetrable gridlock becomes an increasingly common part of the human experience. But managing traffic isn’t just a human problem. From the tunnels built by termites to the enormous underground networks built by fungi, life forms have evolved incredible ways of solving the challenge of moving large numbers of individuals and resources from one place to another.

But how do natural systems – which lack engineers or in some cases even brains – build and manage their transportation networks?

Building a transport network

Perhaps the most familiar animal transport systems are the trail networks of ants. As ants walk through their environment they leave behind tiny droplets of an attractive chemical called a pheromone. Other ants are attracted to the chemical bouquet and as they follow it they add to the trail by leaving their own droplets of pheromone. Like Hansel and Gretel leaving a trail of breadcrumbs, ants use their trails to find their way back home.

The Argentine ant (Linepithema humile) builds chemical trail networks that connect their nests using the shortest possible path. Connecting points via the shortest path saves on construction costs by using less material and requiring less effort.

Argentine ant trails connect nests using an approximation of the shortest path. The grey lines are ant trails visualised by overlaying several photos of the trail system. The inset shows the actual shortest path solution.
Tanya Latty- supplied

Yet calculating the shortest path between a set of points is a very difficult task. So how do ants, which have brains smaller than a pinhead, figure out the solution?

The answer is elegant in its simplicity. Short, direct paths are faster to traverse, and so more pheromone gets deposited by the higher density of ants. As ants are more likely to follow stronger pheromone trails, shorter, more direct trails attract more ants than do long meandering trails.

Meanwhile, fewer and fewer ants travel along the long paths, as they are attracted away by the stronger, shorter path. Eventually the longer paths disappear altogether due to evaporation, leaving only the direct routes. This simple mechanism allows small-brained Argentine ants to solve a difficult problem.

Australian meat ants (Iridomyrmex purpureus) take trail-building to the next level. Meat ants diligently cut away all vegetation from their trails, creating a smooth path. Unlike Argentine ants, meat ants do not connect their nests using the shortest possible route. Instead they build a network that includes extra “redundant” links.

Meat ants clear the grass from their trails and nest.
Nathan Brown, Author provided

Connecting points with the shortest path takes less time and uses less energy, but it would also result in a fragile network; any damage to any trail would isolate one of the nests.

This is less of an issue for Argentine ants, which can rapidly repair any damage to their trail system by depositing more pheromone droplets. For meat ants, however, damage to the system takes more time to fix. So rather than building a cheap but fragile network, meat ants build networks whose structure neatly balances the competing demands of cost and robustness.

Walking in lanes

In most human road networks, traffic flows are organised by dividing traffic into lanes where all the cars travel in the same direction. The army ant (Eciton burchellii) also uses lanes – two outer ones for outbound traffic, and one inner lane for nest-bound traffic.

But how do the army ants organise this? Lanes form because ants heading to the nest often carry heavy loads and so tend not to turn away during head-on collisions. Ants leaving the nest tend to veer away from their heavily laden sisters and so end up in the outer lanes.

Again, a simple set of behavioural rules allows ants to ensure they have a fast, efficient transport system.

Pothole pluggers

Potholes are an annoying and jarring part of driving that can slow traffic to a crawl. So when workers of the army ant (Eciton burchellii) encounter uneven surfaces, they take one for the team and plug it with their living bodies. Workers even match their size to the hole that needs filling.

Teams of ants cooperate to fill larger holes. Ants will even form bridges to span larger gaps. They adjust the width, length and position of the bridge to accommodate changes in traffic.

The result of these hardworking ants is a smooth, fast-flowing transport system that works even over the bumpiest terrain.

Humongous fungus

It’s not just insects that build transport networks. Brainless organisms such as fungi and slime moulds are also master transportation designers.

Fungi build some of the biggest biological transportation systems on Earth. One giant network of honey fungus (Armillaria solidipes) spanned 9.6km. The network is made up of tiny tubules called mycelia, which distribute nutrients around the fungi’s body.

The honey fungus is connected by vast underground transportation networks, spanning many kilometres.
Armand Robichaud/Flickr, CC BY-NC

Slime moulds – which are not fungi but giant single-celled amoebas – use a network of veins to connect food sources to one another.

In a highly creative experiment, researchers used tiny bits of food to make a map of the Tokyo metro system, with the food representing stations. Amazingly, the slime mould quickly connected all the points in a pattern that closely matched the actual Tokyo metro system. It seems slime moulds and engineers use the same rules when constructing transport networks – yet the slime mould does it without the aid of computers, maps or even a brain!

Slime mould form a map of the Tokyo railway system.

Nature has found many different solutions to the universal problem of building and managing a transport system. By studying biological systems, perhaps we can pick up a few tips for improving our own systems.


The ConversationYou can find other articles in the series here.

Tanya Latty, Senior lecturer, University of Sydney

This article was originally published on The Conversation. Read the original article.

Eradicating fire ants is still possible, but we have to choose now


Daniel Spring, University of Melbourne; Jonathan Keith, Monash University, and Tom Kompas, University of Melbourne

Australia needs to spend millions of dollars more to eradicate one of the nation’s worst invasive species, the fire ant, according to recent reports.

Fire ants, first detected in Brisbane in 2001, pose a major health and agricultural risk. A recent independent review of the eradication program recommended that A$380 million be spent over 10 years to eradicate the ants, on top of the A$330 million already spent since 2001.

Improvements in knowledge and control methods mean that eradicating the Australian invasion is challenging, but still potentially feasible. We now face a stark choice.

Lessons from previous attempts

The fire ant eradication program began in September 2001 after the species was detected at two locations in Brisbane. By that time, it may have been present for at least five years or perhaps even longer, and large areas were already infested. Fire ants had never been eradicated from areas this large.

However, improved eradication methods mean we have increased the chances of eradicating larger invasions.

Most of the original funds were spent on pesticides and monitoring areas with likely infestations. Monitoring information was used to estimate how far the invasion had spread (“delimitation”) and management efforts were focused on the delimited area.

The early years of the program showed that large infestations, such as those at the Port of Brisbane and Yarwun, can be eradicated when the geographic range of the infestations is known.

However, when this is not the case, undetected nests beyond the known infested area can spread unchecked. In a published reconstruction of the invasion we estimated that undetected nests existed a relatively short distance beyond the delimited area.

Had those nests been detected by monitoring a larger area over the first few years of the program, the ants may already have been eradicated. However, the initial focus on intensively treating known infestations rather than expanding the monitored area reflected the best available scientific advice at the time.

It also reflected an urgent need to protect people from the potentially serious health consequences of coming into contact with fire ants in areas known to be infested.

Pustules caused by fire ant stings.
Daniel Spring, Author provided

Is eradication still possible?

Although the invasion now occupies a larger area than it did when the program began, fire ant numbers have effectively been suppressed and some individual infestations have been eradicated. These facts, and the availability of a cheaper monitoring method involving remote sensing with airborne cameras, have kept alive eradication hopes.

A recent meeting of agricultural ministers agreed with the finding of the independent review that eradication remains technically feasible.

The review’s recommendation that eradication program funding be increased is a logical response to the invasion’s expansion. The expansion not only increased the area that requires management, thus increasing costs, but also showed that the areas previously searched and treated each year were too small to achieve eradication, implying there was insufficient annual funding.

Geographic expansion of the invasion cannot continue much longer without the invasion becoming too large to eradicate. The review panel’s finding that increased funding should be made available soon is therefore timely.

A lack of monitoring during the early years of the program led to the erroneous conclusion in 2004 that eradication was imminent, when in fact the invasion was expanding in area. To avoid this mistake being repeated, substantial monitoring will be required beyond known infestations and monitoring data will need to be assessed with reliable statistical methods.

In a recent report we wrote to help the eradication program, we showed that the invasion boundary can be estimated with a high degree of confidence if adequate monitoring data are available.

Pesticide treatment and monitoring will underpin eradication efforts. We need highly sensitive monitoring methods, including sniffer dogs and trained spotters, to confirm absence of fire ants in and near treated locations.

A large enough area should be monitored to ensure all fire ant colonies are found and removed. We need continued support for community members to report fire ants, particularly in urban areas. Remote sensing will be needed in less developed areas where contact between people and fire ants is less likely.

A stark choice

The choice is to continue eradication efforts or live with fire ants forever. Living with fire ants will incur large costs for agricultural producers and households.

The most recent cost-benefit analysis of the program estimated that if these costs were added up over each of the next 70 years they would exceed A$25 billion in today’s dollars.

Over half these estimated costs arise from damage to agricultural activities, with household losses being of a similar magnitude.

Large numbers of people are likely to come into contact with fire ants if the species is left unchecked. Environmental damages could also be substantial. These losses far exceed estimated eradication costs.

The review panel’s report makes it clear that we face an urgent choice between increased eradication funding or living with fire ants. There is not much time left to make this choice.

The Conversation

Daniel Spring, Research Fellow, School of Biosciences, University of Melbourne; Jonathan Keith, Associate Professor, School of Mathematical Sciences, Monash University, and Tom Kompas, , University of Melbourne

This article was originally published on The Conversation. Read the original article.