ANTics: Rainforest ants

Entry in journal 14th March 2007.
Now in Cusco. Before I forget, some things about the rainforest…

The leaf-cutter ants
Every time you walk, day or night, there are ants underfoot, usually travelling in long lines. My favourites are the leaf-cutter ants. They are most active at dusk or in the night. Lines which are one or two ants wide in the day become express highways ten ants wide. They follow the same paths so often that it is easy to see their “roads” as clean lines along the forest floor devoid of leaf litter and debris.

Ant nests

They cut the leaves high up in the tree canopy, carefully carry them down the trees and hundreds of metres across the forest floor back to their nests. Allegedly all this effort is to collect leaves is to grow a fungus with which to feed the ant-nest frog. I’ve heard these frogs chirping away when it rains but I’ve never actually seen one. I think they hide inside the ants' nest. It’s unclear whether this relationship is commensal or parasitic in nature. It doesn’t seem to be a symbiosis.

Leaf-cutter ants cut nice semi-circles from the leaves. They cut with their mouths and use a leg to hold the edge of the leaf as a guideline. This way they get nice even pieces. Well, most of the time. The veins of the leaves seem to be particularly tough and offer a challenge. Often the leaf will be left half-cut where a vein has been encountered. Several ants might give it a try in the same place, but it seems easier to start anew than to chomp through such obstacles. They also carry the leaves in their mouths.

Ants cutting a leaf. See how it uses a leg to hold the edge of a leaf. Top right you can see a cut that got as far as the vein

Where they can, all the ants like to take the easy path across the forest floor. This might be across fallen logs or along the compacted soil of human-made trails. I’ve seen leaf-cutter ants and army ants trails criss-crossing along our forest trails for literally hundreds of metres before disappearing off into the undergrowth.

leaf cutter ants prefer an easy path

Trail of leaf cutter ants at night (9:15 pm )

Along with the worker ants are smaller ants who run up and down the line of leaf-carrying ants. Maybe they are the supervisors. Sometimes these tiny ants will hitch a lift on the leaves being carried by the larger ants. I saw one poor ant struggling to carry a large piece of leaf with eight or nine smaller ants clambering over it!

Worker ants carrying leaf in their mouths. Smaller "communicator" ants nearby

As well as carrying leaves, I also saw these ants carrying grains of soil, reminiscent of “Antz” the animated movie. Lots of ants would be coming from a hole in the ground, the entrance to their nest, each carrying a grain of red soil. The soil would be carefully deposited and the ant would return back into the ground, presumably for more.

Army ants
Army ants march along the forest floor in long, long processions. I think the entire colony may move all at the same time. They often have bi-coloured bodies, black with red or orange. I’ve seen their trails, several ants wide of hundreds of metres. That’s thousands of ants! If each ant is a centimetre long (or at least there is a centimetre between the head of one ant and the head of the next), then there are 100 ants per metre, but the trail is often 4 or 5 ants. 500 ants per metre for 100 metres is 5000 ants! 200 metres is 10 000 ants! No wonder they have earned such a fierce reputation.

Army ants, bi-coloured body

Although they travel fast and in long lines, they are not just moving, they are also on the hunt! If you break the line, the ants will quickly pile up around you. Even if you step heavily near the line, several ants will break away to investigate the source of disturbance. I imagine that if it is a small animal (small, that is, compared to humans, huge compared to the ants), then it will quickly be overwhelmed by ants and carried along as food. I think the Nac Mac Feegles operate in the same way. If you break the line or stamp near it and then stand still for a few moments, perhaps to watch an interesting bird, or take a photo of a particularly interesting flower, then you are likely to find yourself covered in ants as they swarm up your boots to investigate. No foe is too large! Especially if it is daft enough to stand still long enough for 10, 0000 ants to cover it! If you’re not wearing boots or, indeed, tough trousers, you are likely to notice these ants very quickly. They have an extremely powerful bite and don’t hesitate to use it. Walking in flip-flops in the forest is not to be recommended. Even if you watch where you tread, and are careful to avoid the marching line, sometimes there are simply so many ants covering the path that there is really no option but to tread on a few. Then – beware!

Trail of army ants (about 10 ants wide)

I got bitten once or twice and it’s very, very painful. Well, at least it’s painful in the short term. They do at least disappear faster than the mosquito bites. Apparently the mandibles of the ants are used by some people as stitches for deep cuts. You hold the ant, it bites (hopefully with one jaw part either side of the cut). It doesn’t let go. Even if the body is removed from the head. Although I haven’t witnessed the ants being used this way, I have no trouble believing it’s true because I’ve seen an ant head with the mandibles embedded deep into the foam of my friend, Geertje’s, flip-flops. It took quite a bit of pulling out, I can tell you. It would make an excellent wound-stitch!

Looks like a soldierto me. Big mandibles!

Sometimes, I’ve seen the advancing “head” of a colony of ants. Just like in TV documentaries, it forms a fan-shape as several lines of ants branch out to investigate new areas. As with all the ants I’ve seen, there is a relay. The ants don’t just move in one direction, there are always a few ants travelling in the opposite direction to the main colony. It seems that the ants will always stop briefly head-to-head as they pass. I can only feel that they are communicating with one another. The “communicator” ant, who is moving against the tide of ants, will stop briefly to “talk” to every ant that is going in the other direction (except occasionally if one ant is a bit too far away). Who knows what information is being passed on? Are you ok? This is a good way to go! Keep in line there!

Anyway, the army ants send out branches to investigate and these often have a greater relay of ants than the colony marching through the forest. I’ve watched them try to invade our bungalow (living quarters). Nasty chemicals act as a deterrent. The first time I saw them making a beeline for my bedroom I was painting. A few drops of paint thinner scattered perpendicular to the direction they were advancing towards quickly prevented them from investigating any further. When the ants got to within a few inches of the chemical, it retreated in disgust for ten or twenty inches and then advances again in a different direction.

Insect repellent, unsurprisingly, also works. I watched a tourist spray some in the middle of an advancing line. We stepped well back to avoid the ensuing chaos, as the ants coming next struggled to find their direction. Eventually some of the “communicator” ants travelling backwards along the line found the tentative advances of their stricken colleagues, and the line was reformed. So perhaps the purpose of their communication is “are you ok?”

But where are they going? At least some of the time, they are looking for a new home. One day (admittedly not long after I’d deterred them from our bungalow), they found the manager’s bungalow and formed a new home there, much to the interest of the tourists and the horror of Vanessa who was sleeping just above them.

Army ant nest, about 150 cm high

The ants’ nests are fascinating. They are living structures made of thousands and thousands of ants all of whom seem to be moving. The spaces between the ants are occupied by other ants and the whole forms a great mass, tens of centimetres high. However many ants I might have seen along a few hundred metres of our forest trail, there are many, many more on their own trails within the forest. There could easily be millions of them. Eager tourists ask if these are the same ants that can devour a cow in a few hours, but I think maybe they’ve been watching too much telly. Mostly though, small creatures; insects; amphibians and mammas best watch out....


The Isula Ant
Also known as the “bullet” ant, these are the largest of the rainforest ants. Each one is easily 3 or 4 centimetres long. Their bite is venomous and can induce fever in humans. It’s possible that a bad reaction to this bite can result in death. However, accounts vary. Gino, the crazy entomologist, said he experienced a minor irritation for a few hours. Yulma, Vanesa´s young niece, told me she had a fever for 3 days after being bitten by one. Regardless of the possibilities, I did my best to avoid being bitten.

Isula ant on leaf

For size: same leaves with my finger when the ant is far, far away.

Wariness is the watchword. They are normally solitary hunters, unlike the other ants, and it’s worth looking twice at ant tree branches or trunks before grabbing hold. You never know when there may be an Isula ant lurking on the other side. Occasionally, however, I saw 20 or 30 individuals moving through the forest together. Gino assured me that this was the entire colony on the move. Personally, I think it may be just a squadron. A million of these ants could probably finish off that cow!

Squadron of Isulas on the move!