Lab Notes: The native ants that take down cane toads

Australia Broadcast Center

21 hours ago

Belinda Smith: It's National Science Week. And this year ABC Science is celebrating the slimy, bitey and downright bizarre creatures that never get featured on postcards. We're shining a spotlight on our underrated animals. And as far as I'm concerned, one of the most underrated creatures is the meat ant. When I was a kid growing up in Western Victoria, I'd often see bird or lizard carcasses absolutely crawling with meat ants, their bones being picked completely clean. Look, I know, meat ants don't sound like the most endearing creatures. But it turns out they're not just aggressive, flesh-tearing fighters. They're also farmers, architects and the best bit of all, cane-toed exterminators. Hi, I'm Belinda Smith and you're listening to Lab Notes, the ABC Radio National show that dissects the science behind new discoveries and current events. To help me convince you that meat ants are underrated is Peter Yeeles, an entomologist and ecologist at James Cook University. Alright, first things first, what are meat ants?
Peter Yeeles: Yeah, so meat ants, they're only found here in Australia and only on the mainland. They're not on Tasmania. They're quite a large ant, so sort of depending on the species, they range from about 8 to 12 millimetres. And it's a species complex, so it's actually made up of between six and seven species, depending on who you speak to. But the majority of meat ants that people will see, especially in the southern part of the country, is a species called Iridomyrmex purpureus.
Belinda Smith: Yeah, Iridomyrmex means rainbow ant, doesn't it? And purpureus means purple, which is really descriptive of what the ant looks like.
Peter Yeeles: Yeah, yeah. So if you look at them from a distance, they just sort of look like a generic large ant with a bit of red and a bit of black. But if you look at them closely, you can see that they're sort of red on their thorax and head. They've got this amazing blue iridescence, which gives them, in combination with that red, this beautiful purple look.
Belinda Smith: And they've also got some quite fearsome looking jaws on
Peter Yeeles: them too. Absolutely. Yeah, yeah. They don't have a sting, so instead of having a sting, they can spray chemicals as a defence. And they have large jaws, which they can use to defend themselves, their colony and also for processing food.
Belinda Smith: Right, OK, the meat ant sounds more like a dinosaur and less like an ant. Are they as aggressive as I'm imagining?
Peter Yeeles: They're super aggressive. They're very dominant within most of the ecosystems that they can be found in, very competitive. They get their name meat ant from their sort of propensity to strip vertebrate carcasses of meat. And even farmers used to drop dead farm animals near a meat ant nest and they'd clean it up for them.
Belinda Smith: Real clean-up crew, sort of like a forensics team almost. Yeah, yeah, exactly. In a kind of grim way. So do they only eat meat?
Peter Yeeles: No, so they are quite generalist in terms of what they consume. So the colony is sort of divided into two main components. You've got the worker ants, which are the ones that you see. And then back held in the colony, you've got lots of larvae. So they're the baby ants essentially. And the baby ants need lots of protein. So they consume the sort of the dead insects and things that the workers bring back and the carrion, the meat. While the worker ants primarily feed on carbohydrates, so sugars. And they get those from flowers and from tending bugs, hemipterans and aphids and things like that up in the tree canopy.
Belinda Smith: Yeah, meat ants are farmers. And they're livestock are special sugar-producing insects.
Peter Yeeles: They're called hemipterans or bugs, we call them bugs. They drink tree sap. So they'll sit on trees and on plants and they've got a long proboscis that they'll use to drink tree sap. But tree sap has lots of sugar in it compared to what the bugs actually need. They only need a little bit of sugar. So they sort of concentrate and expel the excess tree sap. And we call it honeydew. And ants absolutely love honeydew. So they have learned to essentially farm the hemipterans. There are species of ants that will move them around to find the best place on the plant to get the sap. They'll defend them from predators. There are even some when the queen has a mating flight, will carry a hemipteran with her for when she founds her new colony so they've already got hemipterans to start off with.
Belinda Smith: Meat ants also like to feast on seeds, which is mutually beneficial for the plants and the ants. So some
Peter Yeeles: seeds have like this fatty growth on it called an eliosome, which is part of the seed. But these plants have evolved to have this eliosome larger and fattier than on other plant species. And they do that to attract ants. So meat ants, for example, will pick up the seed because it's got this fatty body and they'll take it back to consume it. They'll eat the fatty body, but they don't eat the seed. The seed's got the very hard seed coat so it's not edible to the ants. So once they've eaten that fatty eliosome, they'll dispose of the seed, usually in like a garbage heap essentially, just outside the nest, and disperse that seed for the plant away from its parent.
Belinda Smith: When I think of meat ants, I tend to think of their nests. They're just these beautiful rounded domes cleared of most stuff. But how big can they get? I imagine we're only just sort of seeing a tiny proportion of what a meat ant colony would look like from the surface. They
Peter Yeeles: can be relatively deep, sort of up to a couple of metres, but generally their size is sort of laid out over the landscape. So most meat ants are what we call polydomous. So they'll have one queen usually, and she's held in one central nest. And then radiating out from that nest will be sort of a network of cleared pathways which have satellite nests. So they'll have multiple nests for that one colony, for that one queen. And they can be spread out over quite a large distance as well. So there's plenty of records of meat ant colonies with a series of nests that stretch over half a kilometre across. Oh my gosh. They can be quite large. They travel quite a long way as well when they're sort of foraging. So we've seen them in Western Australia travelling well over 100, 120 metres just to get food. So they can spread quite a long way from that central nest.
Belinda Smith: Now are meat ants dangerous to humans or just occasionally annoying?
Peter Yeeles: Yeah, they're not really dangerous, but they're just a nuisance. So often when you go camping or something like that, if you accidentally put your tent near a meat ant mound, it's pretty miserable, and I think you'd end up having to move. They've got quite a nasty bite, especially when they're very numerous and they're crawling up your legs. And
Belinda Smith: they certainly know how to track down food.
Peter Yeeles: They're very efficient foragers, so they'll be spreading out from those central place nests quite a long distance looking for food. And when they find food, they'll travel back to their nest, leaving a pheromone trail, which all of the nest mates will then follow back to the food to consume it as quickly as they can.
Belinda Smith: This voracious foraging isn't limited to native food sources. They attack invaders too. I
Peter Yeeles: think probably the most famous one would be meat ants interacting with cane toads. So some researchers at the University of Sydney found that meat ants were able to kill and consume young cane toads, which are obviously quite poisonous to most other animals that try to eat them. They found that meat ants consumed these baby cane toads, and there has been some research into looking at how those meat ants could be utilised to try and control cane toads when they're in very high densities, high populations, potentially moving meat ants to around billabongs and waterholes where the cane toads lay their spawn.
Belinda Smith: How fascinating. So meat ants just don't... They're not affected by the cane toad poison at all?
Peter Yeeles: No, I'm not actually aware of the mechanism. I don't know whether it's that they consume parts of the cane toad which aren't toxic, or whether they're just immune to that toxin, I'm not sure.
Belinda Smith: So could the meat ant be a practical solution to a cane toad problem?
Peter Yeeles: I think that the challenge involved in utilising meat ants as a control for cane toads is primarily going to be associated with moving and manipulating the locations of the ants. It's quite difficult to move ant colonies around and then have them established because they'd be moving into communities which are already established.
Belinda Smith: Are you aware of any trials or any results that might have come out of...?
Peter Yeeles: I'm not aware of whether that's been successful yet or not. Yeah, that's Rick Shine and Georgia Ward-Fears' work. It'll be very interesting to see though.
Belinda Smith: Where does the meat ant rate in terms of your favourite ant species?
Peter Yeeles: I'd probably be pretty high. I guess I'm fascinated by ants that have these abilities to influence and change the habitats that they live in. So meat ants are definitely one of those.
Belinda Smith: And meat ants are definitely underrated, that's very clear.
Peter Yeeles: Ants in general, they're one of the most ecologically important animals that we have. There was a famous entomologist in America who once said that if you were to remove all of the birds and mammals, many communities would continue functioning pretty much as they are now. But if you were to remove all of the ants, you'd see these sort of broad scale changes to how those communities function.
Belinda Smith: That was Peter Yeeles, an entomologist and ecologist at James Cook University. And thank you for listening to Lab Notes on ABC Radio National, where every week we dissect the science behind new discoveries and current events. I'm Belinda Smith. This episode was produced on the lands of the Wurundjeri and Menang Noongar people. Fiona Pepper's the producer, and it was mixed by Ross Richardson. Catch you next week.