Ants: Australia’s gift to us

By Elizabeth Newton, Class of 2016

If you asked a person to think of Australian wildlife, the animals that are likely to come to mind are marsupials like koalas and kangaroos. If you encouraged them to keep thinking, next they might bring up snakes. Ultimately though, most people think of spiders. “I want to visit Australia, but then I remember they have spiders…” is an often-repeated sentiment.

Sure, we do have the notorious red-backs, funnel webs, and surprise car huntsmans. I can imagine these would be quite shocking for someone coming from a place where the largest spider you’ll ever encounter is the size of a $1 coin. But I think people have really got it wrong on what represents our wildlife. Travelers spending any time in a natural Australian setting are quickly going to realise spiders are the least of their worries. What they truly need to expect are ants. Lots of ants.

They range from the huge and aggressive bull ants to the small, but often equally zealous black ants. The variety is endless and Australia ranks pretty well in terms of diversity on a world scale: currently our continent contains 1,300 different ants making up nearly 10% of the total known species in the world. And this is only amongst the scientifically described species, with many more yet to be discovered.

But think about it. When you go camping, one of the considerations on pitching a tent is to make sure it’s away from ant nests. Then follows a mantra of “keep it zipped up or ants will get in!” I’d personally rather a spider in my tent than one of these:

An alert bull ant (Myrmecia pyriformis); a formidable creature growing to 3 cm long. They don’t call them ‘inchmen’ for nothing! Image by author.

I am in the habit of checking the ground whenever I stop anywhere in the bush. I learnt the hard way. Once, while admiring an orchid, I was interrupted by a red-hot needle to the ankle. Looking down, I beheld a bull ant frantically stinging me again and again. Another time, I was doing vegetation transects on a hill that was entirely covered by the nests of angry ants. I had no choice but to stand still as I counted and measured plants while they furiously punished me for encroaching on their territories. But it would have to be the moment that a small, black ant ran out of my bike helmet (of all places!) and bit me on the eyelid that made me realise the real terror of Australia.

Since then however, my respect for ants has only grown and my frustration diminished as I learn more and more about them. Australia’s ants are actually really cool.

Ant structure

Ants have lots of nifty features which enable them to exploit any environment and dominate a lot of Australia’s fauna.  Bulldog ants (Myrmecia nigriceps) for example, have excellent binocular vision and are sensitive to motion, as you might notic if you encountered them. They can even discriminate the size of threatening objects, an important ability for an ant that will often run out to attack something approaching the nest. Another thing many Australian’s know about bull ants is their potent venom which can induce anaphylactic shock in some people when stung. And not many other places in the world get to enjoy bull ants like we do; the genus Myrmecia is almost entirely endemic to Australia.

Spiny ants (genus Polyrhachis) are aptly named, their bodies bearing large thorns which they use for defence, as they lack a sting and have comparatively small jaws. When harassed, these ants will often choose to hunker down over running away, curling their bodies so that their spines stick outwards. As a bonus, they’re quite gorgeous.

Polyrhachis (ammon?) by Elizabeth Newton
Golden-tailed spiny-ant (Polyrhachis ammon) cleaning. What lovely golden hair it has! Image by author.

Curious behaviour

Many species of Australian ant also display some pretty unique and interesting behaviours.

Our green tree ants (also called weaver ants) (Oecophylla smaragdina) construct large aerial nests using the living leaves of bushes and trees. The process by which they do this is simply amazing. Using their own larval young as gluesticks, they haul leaves many times their size together before binding them with silk. Apparently these nests, dropped whole (ants included) into a billy, make excellent tea.

You may be familiar with the giant nest surfaces of the meat ant (Iridomyrmex purpureus): suspiciously bare patches commonly found in the bush which on closer inspection, are carefully curated layers of gravel. Upon these open spaces race hundreds of individuals made up of the forager and display castes of the nest. These display ants pretty much do just that, spending all their time slowly circling one another and lifting legs in a continous ritualised dance around the border of the territory. Their purpose is to define their territory borders, resolving disputes with outsiders in a way that is less costly than outright fighting.

Meat ants (Iridomyrmex purpureus) engaged in ritualistic displays. Image by author.

Ecosystem services

Ants perform very important roles in the environment and are considered to be ‘ecosystem engineers‘, contributing significantly to pollination, plant selection, nutrient cycling, and food web dynamics. Ants are frequently used as bioindicators (organisms that can reveal the health of habitats and ecosystems) due to their environmental importance.

In Australia, there are some particularly interesting roles performed by ants in the form of mutualisms (relationships where both participants benefit). Myrmecochory is the spreading of plant seeds by ants and provides a valuable service for many Australian plant species, particularly wattles (Acacia species). To collect seeds, ants are enticed by the fatty substance attached to the top, the elaiosome. It’s like ant chocolate, rewarding the insects for transporting the seed away from the parent plant and to a safe nest underground where the seeds can remain safe from being eaten or destroyed in a bushfire until the seedling emerges.

A unique mutualistic interaction between butterflies and ants can also be found out in the Australian bush. Ants are typically predators of caterpillars, but some species in the genus Iridomyrmex are actually needed by butterfly larvae to complete their lifecycle. The relationships between lycaenid butterflies and Australian ants are complex, with caterpillars producing different substances from their bodies depending on whether they want to attract, appease, reward, or even repel their carer ants. In return for a reward, the ants protect the larvae from predators and parasites. The lycaenid-ant relationships vary greatly, however, with some butterfly species actually parasitising the hard work of the ants!

Iridomyrmex anceps tending an imperial hairstreak butterfly (Jalmenus evagoras) caterpillar. Image credit Mark Moffett.

Love your ants

It’s surprising that Australia isn’t known for its ants as it is for its snakes and spiders (albeit negatively) and I think this is a real shame. We are fortunate to share a country with so many fascinating species and I encourage everyone to take a second longer to appreciate our little friends (who knows, you might even be looking at an undiscovered species!)

Because although they may be terrors some of the time, ants are certainly an awesome part of Australia’s wildlife.

Monomorium kilianii by Russell Long
Just an indistinct, tiny black ant till you get up close. Monomorium kilianii by Russell Long, used with permission.

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Read more: The Mark Elgar Lab at the University of Melbourne produces excellent research on Australian ants, including meat ants and lycaenid butterfly-ant relationships.