Hidden Kingdom, Part Two

(Via:)
(Via: Livingroutes.org)

Common Name: Leafcutter Ants

A.K.A.: Genera Atta and Acromyrmex of Tribe Attini

Vital Stats:

  • Fungi grown by leafcutter ants come from the family Agaricaceae
  • Ant species can maintain their association with a specific fungal cultivar for millennia
  • Neither the ants nor the fungal cultivars can survive outside of the symbiosis
  • Some ant species are capable of completely defoliating a small tree in under a day

Found: Humid forests of Central and South America

Leafcutter Map

It Does What?!

Last week, we looked at leafcutter colonies, their various castes, and the impressively long lives of ant sperm. But obviously, leafcutter ants are known principally for one thing- cutting leaves. This they do on a grand scale, forming lines of thousands upon thousands of ants, dutifully toting chucks of foliage back to their colony. Why? To fertilize their fungus, of course! Much as we like to think of agriculture as one of the crowning achievements of mankind, the fact is, ants came up with it much earlier than we did. About 50 million years earlier, actually. (But they haven’t figured out how to deep-fry anything yet, so there’s that, I guess.)

caption (Via: Wikimedia.org)
The fungus is hungry.
(Via: Wikimedia.org)

When a young queen leaves her original colony to found a new one, she carries in her mouth a small piece of fungus to use as a starter culture (think yogurt or sourdough bread) for the colony’s gardens. Initially, she will care for this culture alone, but once the first generation of workers is born, they will take over the task from that point on. Since fungi don’t photosynthesize, they’re perfectly happy in a pitch-black underground garden, but they still need nutrients with which to grow, and dead vegetation is their food of choice. As the larger worker castes return with leaf (and flower) fragments up to three times their own mass, the minima gardeners clean away any outside fungal spores and chew the vegetation into smaller and smaller pieces. They then mix the shredded leaves with fungus and add the mixture to the garden. And, just for an extra fertiliser kick, they mix in their own faeces. Waste not, want not, right?

With all the workers coming and going, and so much foreign vegetation entering the colony, infections of the garden by competing fungal spores are inevitable, despite the ants’ best efforts. One such invader is the fungus Escovopsis, a parasite of other fungi, which can decimate a colony’s food supply and, in the case of young and vulnerable colonies, sometimes cause them to fail entirely.

caption (Via:)
I use the term “garden” loosely…
(Via: Marietta College)

But the ants have a secret weapon: bacteria. These adaptive little farmers actually carry around a ready supply of antimicrobial compounds right on their bodies. The bacterium in question, Pseudonocardia, grows directly on the ants’ exoskeletons and, researchers suspect, is nourished by a substance excreted through the ant’s glands. In return, Pseudonocardia produces a compound that the farmers can spread on invading fungus, killing it without damaging their food source. Symbioses within symbioses… and these are just the ones we know about.

Meanwhile, outside the colony, another fascinating parasite threatens the workers. Known as phorid flies, or ant-decapitating flies, you can probably guess why these things are a problem. Female phorid flies land on the backs of the larger worker ants as they travel to and from their leaf harvesting sites, laying eggs on the worker’s thorax. Once the eggs hatch, the larvae work their way into the ant’s head and start to eat the tissue surrounding the brain, eventually moving on to the brain itself (causing aimless wandering behaviour similar to that caused by the zombie ant fungus). Finally, the young parasites secrete an enzyme which causes the ant’s head to fall off completely, leaving them a convenient vessel in which to finish their development into adults.

caption(Via:)
They’ve evolved everything but the ability to look behind them.
(Via: Dayvectors.net)

Not to be outsmarted (by anything, apparently), leafcutter ants instituted a policy of defensive piggyback rides. Workers on the foraging path carry tiny minima ants on their backs as they travel. The minimae are too small to be useful hosts for the phorid fly, and so are able to fearlessly attack the flies as they approach, keeping the foragers safe. And not to lose an opportunity for increased efficiency, the little passenger will also begin cleaning the leaf fragment as the larger worker carries it home.

So there you have it. Leafcutter ants form colonies of millions, assign specialised tasks to different classes of citizens, grow their own crops, excel at problem-solving, and know how to use antibiotics. Next to humans, they form the largest and most complex societies on Earth. Forget robots and computers, people- if anything’s going to gain sentience and overthrow humanity, my money’s on the ants.

[Fun Fact: They compost, too. At least one leafcutter species maintains ‘outdoor’ waste heaps of discarded leaves and fungus. Special disposal workers (often old or unhealthy ants) turn the heap regularly to speed up decomposition.]

Says Who?

  • www.antweb.org
  • Marietta College Leafcutter Ant Page

  • Dijkstra & Boomsma (2006) Insectes Sociaux 53: 136-140
  • Evison & Hughes (2011) Naturwissenschaften 98: 643-649
  • Evison & Ratnieks (2007) Ecological Entomology 32: 451-454
  • Holman et al. (2011) Molecular Ecology 20: 5092-5102
  • Mueller et al. (2008) Evolution 62(11): 2894-2912
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Hidden Kingdom, Part One

(Via:)
(By: Tobias Gerlach & Jenny Theobald, Via: deepgreenphoto.com)

Common Name: Leafcutter Ants

A.K.A.: Genera Atta and Acromyrmex of Tribe Attini

Vital Stats:

  • 47 species; 15 in Atta, 36 in Acromyrmex
  • Atta ants have three dorsal spines and a smooth exoskeleton, while Acromyrmex ants have four spines and a rough exoskeleton
  • Less than 5% of new queens are able to build a successful colony
  • A maxima may have a head width of up to 7mm (0.28”), while a minima reaches less than 1mm (0.04”); mediae fall somewhere in between

Found: Humid forests of Central and South America

Leafcutter Map

It Does What?!

Once in a while, I come across a species that’s just so strange and interesting, a single post doesn’t seem to do it justice. With that in mind, welcome to part one of the wonderous life of the leafcutter ant.

Let’s begin at the start of it all – a new colony being founded. This happens when a fertile, winged female and several fertile, winged male ants (called drones) are born and grow to maturity. One day, the winged crew will fly away together and engage in what’s called a nuptual flight, where the female mates with several different males (up to seven in some species) while in mid-air. Having accomplished what is literally their only purpose in a short, glorious life, the drones promptly die, while the new queen scouts out a good place to start her colony. Finding it, she yanks off her own wings, never to fly again, as her body starts to break down her flight muscles, using the energy to produce eggs.

caption (Via: )
Nursery duty can be creepy when the babies all look like dead albinos.
(Via: Marietta College)

Ant reproduction is remarkable in that actual mating occurs only once in the queen’s life. The males of her nuptual flight together provide hundreds of millions of sperm that will be the basis for the entire colony to come. At the risk of sounding like a weirdo, ants have amazing sperm. A human sperm cell, under ideal conditions, can survive for up to five days. If they don’t get the job done in that time, they’re finished. The sperm of leafcutter ants, having been collected by the queen, can live for up to thirty years. That’s probably older than a lot of the people reading this. They can spend decades just waiting around in storage for the egg with their name on it. And that’s not all- they come armed. As in, chemical warfare. The seminal fluid of ants contains compounds that can lower the survival of rival sperm (from other drones) while not harming those of the ant they came from. Weaker sperm are thereby killed off early in the game. Of course, this kind of thing doesn’t go on for a long time. The storage organs of the queen contain their own fluid that will neutralize chemical weapons on the way in. Think of it as the metal detector at the door.

Right. So the queen has her new place picked out and the on-site sperm bank is up and running. Time to make a colony. What she needs first are workers. In a small chamber she’s excavated underground, she begins to lay large numbers of eggs. These serve two purposes, because the early hatchers will eat the late hatchers until the food supply gets built up. It pays to be a bit premature when you’re an ant.

(Via: Marietta College)
(Via: Marietta College)

Nearly every worker born to the queen over the life of the colony will be a sterile female, and each will belong to one of three major castes- minimae, mediae, and maximae. These castes will dictate both their size and function in life. Sensing the needs of the colony, the queen can actually control which type of worker she is producing. First come the minimae, which are the smallest caste and will principally tend the underground gardens which are the colony’s food source (more on ant agriculture in part two), as well as acting as nurse-maids for growing larvae. Next are the mediae, which are larger and act as the colony’s foragers, bringing plant material with which to fertilize the gardens, and defending against minor threats or obstacles in the troop’s path. Finally, once the colony has reached a population of several thousand, come the maximae, or soldier ants. These big brutes are up to thirty times the mass of a minima and do all the heavy lifting, carrying bulky items, moving big obstacles, and cutting tough pieces of vegetation. They’re also the last line of defence when something serious threatens the colony or the foraging parties. And because ants are all about organisation, within each caste, there are numerous sub-castes which are responsible for specific duties, depending on which species we’re talking about.

caption(Via:)
Little sisters are annoying no matter what species they are.
(By: Alexander Wild, Via: Alex Wild Photography)

Over time, leafcutter colonies can become impressively large, comprising over 5 million residents- the population of a major human city. It’s amazing to consider that these are kept running smoothly without central authority, technology, or the aid of written or spoken language. Not to mention opposable thumbs.

Tune in next week for a look at leafcutter agriculture, their interesting relationships with symbiotic fungi and bacteria, and why ants give each other piggyback rides to work.

[Fun Fact: The largest leafcutter ant colony on record required the excavation of approximately 40 tonnes (44 tons) of earth and contained thousands of different chambers.]

Says Who?

  • www.antweb.org
  • Marietta College Leafcutter Ant Page
  • den Boer et al. (2010) Science 327: 1506-1509
  • Dijkstra & Boomsma (2006) Insectes Sociaux 53: 136-140
  • Evison & Hughes (2011) Naturwissenschaften 98: 643-649
  • Evison & Ratnieks (2007) Ecological Entomology 32: 451-454
  • Holman et al. (2011) Molecular Ecology 20: 5092-5102
  • Mueller et al. (2008) Evolution 62(11): 2894-2912